Fix PM hibernation in Xen guests

From: Munehisa Kamata <[email protected]>

Guest hibernation is different from xen suspend/resume/live migration. Xen save/restore does not use pm_ops as is needed by guest hibernation. Hibernation in guest follows ACPI path and is guest inititated , the hibernation image is saved within guest as compared to later modes which are xen toolstack assisted and image creation/storage is in control of hypervisor/host machine.
To differentiate between Xen suspend and PM hibernation, keep track of the on-going suspend mode by mainly using a new API to keep track of SHUTDOWN_SUSPEND state.
Introduce a simple function that keeps track of on-going suspend mode so that PM hibernation code can behave differently according to the current suspend mode.
Since Xen suspend doesn't have corresponding PM event, its main logic is modfied to acquire pm_mutex.

Though, accquirng pm_mutex is still right thing to do, we may see deadlock if PM hibernation is interrupted by Xen suspend. PM hibernation depends on xenwatch thread to process xenbus state transactions, but the thread will sleep to wait pm_mutex which is already held by PM hibernation context in the scenario. Xen shutdown code may need some changes to avoid the issue.

drivers/xen/manage.c +4 -0

+
+static int xen_pm_notifier(struct notifier_block *notifier,
+	unsigned long pm_event, void *unused)
+{

drivers/xen/manage.c +3 -0

+	return register_pm_notifier(&xen_pm_notifier_block);
+}
+

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Quoted 16 lines · Anchal Agarwal

From: Munehisa Kamata <[email protected]>

Guest hibernation is different from xen suspend/resume/live migration. Xen save/restore does not use pm_ops as is needed by guest hibernation. Hibernation in guest follows ACPI path and is guest inititated , the hibernation image is saved within guest as compared to later modes which are xen toolstack assisted and image creation/storage is in control of hypervisor/host machine.
To differentiate between Xen suspend and PM hibernation, keep track of the on-going suspend mode by mainly using a new API to keep track of SHUTDOWN_SUSPEND state.
Introduce a simple function that keeps track of on-going suspend mode so that PM hibernation code can behave differently according to the current suspend mode.
Since Xen suspend doesn't have corresponding PM event, its main logic is modfied to acquire pm_mutex.

lock_system_sleep() is not taking this mutex.

Quoted 8 lines

Though, accquirng pm_mutex is still right thing to do, we may see deadlock if PM hibernation is interrupted by Xen suspend. PM hibernation depends on xenwatch thread to process xenbus state transactions, but the thread will sleep to wait pm_mutex which is already held by PM hibernation context in the scenario. Xen shutdown code may need some changes to avoid the issue.

Is it Xen's shutdown or suspend code that needs to address this? (Or I may not understand what the problem is that you are describing)

Quoted 6 lines

drivers/xen/manage.c +4 -0

+
+static int xen_pm_notifier(struct notifier_block *notifier,
+     unsigned long pm_event, void *unused)
+{

drivers/xen/manage.c int xen_setup_shutdown_event(void) · line 413

Quoted 10 lines

drivers/xen/manage.c +10 -0

+     int ret;
+
+     switch (pm_event) {
+     case PM_SUSPEND_PREPARE:
+     case PM_HIBERNATION_PREPARE:
+     /* Guest hibernation is not supported for aarch64 currently*/
+     if (IS_ENABLED(CONFIG_ARM64)) {
+             ret = NOTIFY_BAD;
+             break;
+     }

Indentation.

drivers/xen/manage.c int xen_setup_shutdown_event(void) · line 422

Quoted 9 lines

drivers/xen/manage.c +9 -0

+     case PM_RESTORE_PREPARE:
+     case PM_POST_SUSPEND:
+     case PM_POST_HIBERNATION:
+     case PM_POST_RESTORE:
+     default:
+             ret = NOTIFY_OK;
+     }
+     return ret;
+};

This whole routine now is

        if (IS_ENABLED(CONFIG_ARM64))
                return NOTIFY_BAD;

        return NOTIFY_OK;

isn't it?

drivers/xen/manage.c int xen_setup_shutdown_event(void) · line 431

Quoted 10 lines

drivers/xen/manage.c +9 -0

+
+static struct notifier_block xen_pm_notifier_block = {
+     .notifier_call = xen_pm_notifier
+};
+
+static int xen_setup_pm_notifier(void)
+{
+     if (!xen_hvm_domain() || xen_initial_domain())
+             return -ENODEV;

I don't think this works anymore.

In the past your notifier would set suspend_mode (or something) but now it really doesn't do anything except reports an error in some (ARM) cases.

So I think you should move this check into the notifier.

(And BTW I still think PM_SUSPEND_PREPARE should return an error too. The fact that we are using "suspend" in xen routine names is irrelevant)

-boris

Quoted 5 lines

drivers/xen/manage.c +3 -0

+     return register_pm_notifier(&xen_pm_notifier_block);
+}
+

Quoted 13 lines · On Sun, Sep 13, 2020 at 11:43:30AM -0400, [email protected] wrote:

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Quoted 6 lines · Anchal Agarwal

Though, accquirng pm_mutex is still right thing to do, we may see deadlock if PM hibernation is interrupted by Xen suspend. PM hibernation depends on xenwatch thread to process xenbus state transactions, but the thread will sleep to wait pm_mutex which is already held by PM hibernation context in the scenario. Xen shutdown code may need some changes to avoid the issue.

Quoted 3 lines

Is it Xen's shutdown or suspend code that needs to address this? (Or I may not understand what the problem is that you are describing)

Its Xen suspend code I think. If we do not take the system_transition_mutex in do_suspend then if hibernation is triggered in parallel to xen suspend there could be issues.

Now this is still theoretical in my case and I havent been able
to reproduce such a race. So the approach the original author took was to take this lock which to me seems right.
And its Xen suspend and not Xen Shutdown. So basically if this scenario happens I am of the view one of other will fail to occur then how do we recover or avoid this at all.

Does that answer your question?

Quoted 7 lines

drivers/xen/manage.c int xen_setup_shutdown_event(void) · line 431

Quoted 5 lines

drivers/xen/manage.c +5 -0

+
+static int xen_setup_pm_notifier(void)
+{
+     if (!xen_hvm_domain() || xen_initial_domain())
+             return -ENODEV;

I don't think this works anymore.

What do you mean?
The first check is for xen domain types and other is for architecture support. The reason I put this check here is because I wanted to segregate the two. I do not want to register this notifier at all for !hmv guest and also if its an initial control domain.
The arm check only lands in notifier because once hibernate() api is called -> calls pm_notifier_call_chain for PM_HIBERNATION_PREPARE this will fail for aarch64.
Once we have support for aarch64 this notifier can go away altogether.

Is there any other reason I may be missing why we should move this check to notifier?

Quoted 7 lines

In the past your notifier would set suspend_mode (or something) but now it really doesn't do anything except reports an error in some (ARM) cases.

So I think you should move this check into the notifier. (And BTW I still think PM_SUSPEND_PREPARE should return an error too. The fact that we are using "suspend" in xen routine names is irrelevant)

I may have send "not-updated" version of the notifier's function change.

drivers/xen/manage.c +3 -0

+    switch (pm_event) {
+       case PM_HIBERNATION_PREPARE:
+        /* Guest hibernation is not supported for aarch64 currently*/

With the above path PM_SUSPEND_PREPARE will go all together. Does that resolves this issue? I wanted to get rid of all SUSPEND_* as they are not needed here clearly.
The only reason I kept it there is if someone tries to trigger hibernation on ARM instances they should get an error. As I am not sure about the current behavior. There may be a better way to not invoke hibernation on ARM DomU's and get rid of this block all together.

Again, sorry for sending in the half baked fix. My workspace switch may have caused the error.

Quoted 4 lines

-boris

Anchal

Quoted 4 lines

Quoted 4 lines

drivers/xen/manage.c +3 -0

+     return register_pm_notifier(&xen_pm_notifier_block);
+}
+

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Quoted 17 lines · Anchal Agarwal

Quoted 16 lines · On Sun, Sep 13, 2020 at 11:43:30AM -0400, [email protected] wrote:

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Quoted 6 lines · Anchal Agarwal

Though, accquirng pm_mutex is still right thing to do, we may see deadlock if PM hibernation is interrupted by Xen suspend. PM hibernation depends on xenwatch thread to process xenbus state transactions, but the thread will sleep to wait pm_mutex which is already held by PM hibernation context in the scenario. Xen shutdown code may need some changes to avoid the issue.

Is it Xen's shutdown or suspend code that needs to address this? (Or I may not understand what the problem is that you are describing)

Quoted 3 lines

Its Xen suspend code I think. If we do not take the system_transition_mutex in do_suspend then if hibernation is triggered in parallel to xen suspend there could be issues.

But you *are* taking this mutex to avoid this exact race, aren't you?

Quoted 30 lines

Now this is still theoretical in my case and I havent been able
to reproduce such a race. So the approach the original author took was to take this lock which to me seems right.
And its Xen suspend and not Xen Shutdown. So basically if this scenario happens I am of the view one of other will fail to occur then how do we recover or avoid this at all.

Does that answer your question?

Quoted 7 lines

drivers/xen/manage.c int xen_setup_shutdown_event(void) · line 431

Quoted 5 lines

drivers/xen/manage.c +5 -0

+
+static int xen_setup_pm_notifier(void)
+{
+     if (!xen_hvm_domain() || xen_initial_domain())
+             return -ENODEV;

I don't think this works anymore.

What do you mean?
The first check is for xen domain types and other is for architecture support. The reason I put this check here is because I wanted to segregate the two. I do not want to register this notifier at all for !hmv guest and also if its an initial control domain.
The arm check only lands in notifier because once hibernate() api is called -> calls pm_notifier_call_chain for PM_HIBERNATION_PREPARE this will fail for aarch64.
Once we have support for aarch64 this notifier can go away altogether.

Quoted 2 lines

Is there any other reason I may be missing why we should move this check to notifier?

Not registering this notifier is equivalent to having it return NOTIFY_OK.

In your earlier versions just returning NOTIFY_OK was not sufficient for hibernation to proceed since the notifier would also need to set suspend_mode appropriately. But now your notifier essentially filters out unsupported configurations. And so if it is not called your configuration (e.g. PV domain) will be considered supported.

Quoted 13 lines

Quoted 8 lines

In the past your notifier would set suspend_mode (or something) but now it really doesn't do anything except reports an error in some (ARM) cases.

So I think you should move this check into the notifier. (And BTW I still think PM_SUSPEND_PREPARE should return an error too. The fact that we are using "suspend" in xen routine names is irrelevant)

I may have send "not-updated" version of the notifier's function change.

drivers/xen/manage.c +3 -0

+    switch (pm_event) {
+       case PM_HIBERNATION_PREPARE:
+        /* Guest hibernation is not supported for aarch64 currently*/

drivers/xen/manage.c int xen_setup_shutdown_event(void) · line 420

Quoted 10 lines

drivers/xen/manage.c +10 -0

+        if (IS_ENABLED(CONFIG_ARM64)) {
+             ret = NOTIFY_BAD;
+             break;
+     }
+       case PM_RESTORE_PREPARE:
+       case PM_POST_RESTORE:
+       case PM_POST_HIBERNATION:
+       default:
+           ret = NOTIFY_OK;
+    }

There is no difference on x86 between this code and what you sent earlier. In both instances PM_SUSPEND_PREPARE will return NOTIFY_OK.

On ARM this code will allow suspend to proceed (which is not what we want).

-boris

Quoted 21 lines

With the above path PM_SUSPEND_PREPARE will go all together. Does that resolves this issue? I wanted to get rid of all SUSPEND_* as they are not needed here clearly.
The only reason I kept it there is if someone tries to trigger hibernation on ARM instances they should get an error. As I am not sure about the current behavior. There may be a better way to not invoke hibernation on ARM DomU's and get rid of this block all together.

Again, sorry for sending in the half baked fix. My workspace switch may have caused the error.

Quoted 4 lines

-boris

Anchal

Quoted 4 lines

Quoted 4 lines

drivers/xen/manage.c +3 -0

+     return register_pm_notifier(&xen_pm_notifier_block);
+}
+

Quoted 21 lines

Quoted 21 lines

Quoted 11 lines

drivers/xen/manage.c int xen_setup_shutdown_event(void) · line 431

Quoted 9 lines

drivers/xen/manage.c +5 -0

+
+static int xen_setup_pm_notifier(void)
+{
+     if (!xen_hvm_domain() || xen_initial_domain())
+             return -ENODEV;

I don't think this works anymore.

What do you mean?
The first check is for xen domain types and other is for architecture support. The reason I put this check here is because I wanted to segregate the two. I do not want to register this notifier at all for !hmv guest and also if its an initial control domain.
The arm check only lands in notifier because once hibernate() api is called -> calls pm_notifier_call_chain for PM_HIBERNATION_PREPARE this will fail for aarch64.
Once we have support for aarch64 this notifier can go away altogether.

Quoted 6 lines

Quoted 2 lines

Is there any other reason I may be missing why we should move this check to notifier?

Not registering this notifier is equivalent to having it return NOTIFY_OK.

How is that different from current behavior?

Quoted 7 lines

In your earlier versions just returning NOTIFY_OK was not sufficient for hibernation to proceed since the notifier would also need to set suspend_mode appropriately. But now your notifier essentially filters out unsupported configurations. And so if it is not called your configuration (e.g. PV domain) will be considered supported.

I am sorry if I am having a bit of hard time understanding this. How will it be considered supported when its not even registered? My understanding is if its not registered, it will not land in notifier call chain which is invoked in pm_notifier_call_chain().

As Roger, mentioned in last series none of this should be a part of PVH dom0 hibernation as its not tested but this series should also not break anything. If I register this notifier for PVH dom0 and return error later that will alter the current behavior right?

If a pm_notifier for pvh dom0 is not registered then it will not land in the notifier call chain and system will work as before this series. If I look for unsupported configurations, then !hvm domain is also one but we filter that out at the beginning and don't even bother about it.

Unless you mean guest running VMs itself? [Trying to read between the lines may not be the case though]

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Quoted 33 lines

Quoted 19 lines

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Quoted 9 lines

drivers/xen/manage.c int xen_setup_shutdown_event(void) · line 431

Quoted 7 lines

drivers/xen/manage.c +5 -0

+
+static int xen_setup_pm_notifier(void)
+{
+     if (!xen_hvm_domain() || xen_initial_domain())
+             return -ENODEV;

I don't think this works anymore.

What do you mean?
The first check is for xen domain types and other is for architecture support. The reason I put this check here is because I wanted to segregate the two. I do not want to register this notifier at all for !hmv guest and also if its an initial control domain.
The arm check only lands in notifier because once hibernate() api is called -> calls pm_notifier_call_chain for PM_HIBERNATION_PREPARE this will fail for aarch64.
Once we have support for aarch64 this notifier can go away altogether.

Quoted 6 lines

Quoted 2 lines

Is there any other reason I may be missing why we should move this check to notifier?

Not registering this notifier is equivalent to having it return NOTIFY_OK.

How is that different from current behavior?

Quoted 7 lines

In your earlier versions just returning NOTIFY_OK was not sufficient for hibernation to proceed since the notifier would also need to set suspend_mode appropriately. But now your notifier essentially filters out unsupported configurations. And so if it is not called your configuration (e.g. PV domain) will be considered supported.

Quoted 4 lines

I am sorry if I am having a bit of hard time understanding this. How will it be considered supported when its not even registered? My understanding is if its not registered, it will not land in notifier call chain which is invoked in pm_notifier_call_chain().

Returning an error from xen_setup_pm_notifier() doesn't have any effect on whether hibernation will start. It's the notifier that can stop it.

Quoted 6 lines

As Roger, mentioned in last series none of this should be a part of PVH dom0 hibernation as its not tested but this series should also not break anything. If I register this notifier for PVH dom0 and return error later that will alter the current behavior right?

Quoted 7 lines

If a pm_notifier for pvh dom0 is not registered then it will not land in the notifier call chain and system will work as before this series. If I look for unsupported configurations, then !hvm domain is also one but we filter that out at the beginning and don't even bother about it.

Unless you mean guest running VMs itself? [Trying to read between the lines may not be the case though]

In hibernate():

error = __pm_notifier_call_chain(PM_HIBERNATION_PREPARE, -1,

&nr_calls);
        if (error) {
                nr_calls--;
                goto Exit;
        }

Is you don't have notifier registered (as will be the case with PV domains and dom0) you won't get an error and proceed with hibernation. (And now I actually suspect it didn't work even with your previous patches)

But something like this I think will do what you want:

static int xen_pm_notifier(struct notifier_block *notifier,
unsigned long pm_event, void *unused)

{

       if (IS_ENABLED(CONFIG_ARM64) ||
           !xen_hvm_domain() || xen_initial_domain() ||
           (pm_event == PM_SUSPEND_PREPARE)) {
                if ((pm_event == PM_SUSPEND_PREPARE) || (pm_event ==
PM_HIBERNATION_PREPARE))
                        pr_warn("%s is not supported for this guest",
                                (pm_event == PM_SUSPEND_PREPARE) ?
                                "Suspend" : "Hibernation");
                return NOTIFY_BAD;

        return NOTIFY_OK;

}

static int xen_setup_pm_notifier(void)

{
        return register_pm_notifier(&xen_pm_notifier_block);
}

I tried to see if there is a way to prevent hibernation without using notifiers (like having a global flag or something) but didn't find anything obvious. Perhaps others can point to a simpler way of doing this.

-boris

Thanks for the above suggestion. You are right I didn't find a way to declare a global state either. I just broke the above check in 2 so that once we have support for ARM we should be able to remove aarch64 condition easily. Let me know if I am missing nay corner cases with this one.

static int xen_pm_notifier(struct notifier_block *notifier,
unsigned long pm_event, void *unused)

{
    int ret = NOTIFY_OK;
    if (!xen_hvm_domain() || xen_initial_domain())
	ret = NOTIFY_BAD;
    if(IS_ENABLED(CONFIG_ARM64) && (pm_event == PM_SUSPEND_PREPARE || pm_event == HIBERNATION_PREPARE))
	ret = NOTIFY_BAD;

    return ret;
}

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Quoted 14 lines · Anchal Agarwal

Thanks for the above suggestion. You are right I didn't find a way to declare a global state either. I just broke the above check in 2 so that once we have support for ARM we should be able to remove aarch64 condition easily. Let me know if I am missing nay corner cases with this one.

static int xen_pm_notifier(struct notifier_block *notifier,
unsigned long pm_event, void *unused)

{
    int ret = NOTIFY_OK;
    if (!xen_hvm_domain() || xen_initial_domain())
      ret = NOTIFY_BAD;
    if(IS_ENABLED(CONFIG_ARM64) && (pm_event == PM_SUSPEND_PREPARE || pm_event == HIBERNATION_PREPARE))
      ret = NOTIFY_BAD;

Quoted 2 lines

    return ret;
}

This will allow PM suspend to proceed on x86.

-boris

Quoted 24 lines · On Tue, Sep 22, 2020 at 12:18:05PM -0400, [email protected] wrote:

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Quoted 16 lines · Anchal Agarwal

Thanks for the above suggestion. You are right I didn't find a way to declare a global state either. I just broke the above check in 2 so that once we have support for ARM we should be able to remove aarch64 condition easily. Let me know if I am missing nay corner cases with this one.

static int xen_pm_notifier(struct notifier_block *notifier,
unsigned long pm_event, void *unused)

{
    int ret = NOTIFY_OK;
    if (!xen_hvm_domain() || xen_initial_domain())
      ret = NOTIFY_BAD;
    if(IS_ENABLED(CONFIG_ARM64) && (pm_event == PM_SUSPEND_PREPARE || pm_event == HIBERNATION_PREPARE))
      ret = NOTIFY_BAD;

    return ret;
}

Quoted 1 line

This will allow PM suspend to proceed on x86.

Right!! Missed it.
Also, wrt KASLR stuff, that issue is still seen sometimes but I haven't had bandwidth to dive deep into the issue and fix it. I seem to have lost your email in my inbox hence covering the question here.

Quoted 2 lines

Quoted 2 lines

-boris

Quoted 20 lines · Anchal Agarwal

Quoted 19 lines · On Tue, Sep 22, 2020 at 12:18:05PM -0400, [email protected] wrote:

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Quoted 14 lines · Anchal Agarwal

Thanks for the above suggestion. You are right I didn't find a way to declare a global state either. I just broke the above check in 2 so that once we have support for ARM we should be able to remove aarch64 condition easily. Let me know if I am missing nay corner cases with this one.

static int xen_pm_notifier(struct notifier_block *notifier,
unsigned long pm_event, void *unused)

{
    int ret = NOTIFY_OK;
    if (!xen_hvm_domain() || xen_initial_domain())
      ret = NOTIFY_BAD;
    if(IS_ENABLED(CONFIG_ARM64) && (pm_event == PM_SUSPEND_PREPARE || pm_event == HIBERNATION_PREPARE))
      ret = NOTIFY_BAD;

Quoted 8 lines

Quoted 5 lines

Quoted 2 lines

    return ret;
}

This will allow PM suspend to proceed on x86.

Right!! Missed it.
Also, wrt KASLR stuff, that issue is still seen sometimes but I haven't had bandwidth to dive deep into the issue and fix it.

Quoted 3 lines

I seem to have lost your email
in my inbox hence covering the question here.

Quoted 1 line

Can I add your Reviewed-by or Signed-off-by to it?

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Quoted 25 lines · Anchal Agarwal

Quoted 24 lines · Anchal Agarwal

Quoted 23 lines · On Tue, Sep 22, 2020 at 12:18:05PM -0400, [email protected] wrote:

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Quoted 16 lines · Anchal Agarwal

Thanks for the above suggestion. You are right I didn't find a way to declare a global state either. I just broke the above check in 2 so that once we have support for ARM we should be able to remove aarch64 condition easily. Let me know if I am missing nay corner cases with this one.

static int xen_pm_notifier(struct notifier_block *notifier,
unsigned long pm_event, void *unused)

{
    int ret = NOTIFY_OK;
    if (!xen_hvm_domain() || xen_initial_domain())
      ret = NOTIFY_BAD;
    if(IS_ENABLED(CONFIG_ARM64) && (pm_event == PM_SUSPEND_PREPARE || pm_event == HIBERNATION_PREPARE))
      ret = NOTIFY_BAD;

    return ret;
}

Quoted 4 lines

Quoted 4 lines

Quoted 1 line

This will allow PM suspend to proceed on x86.

Right!! Missed it.
Also, wrt KASLR stuff, that issue is still seen sometimes but I haven't had bandwidth to dive deep into the issue and fix it.

So what's the plan there? You first mentioned this issue early this year and judged by your response it is not clear whether you will ever spend time looking at it.

Quoted 5 lines

Quoted 4 lines

I seem to have lost your email
in my inbox hence covering the question here.

Quoted 1 line

Can I add your Reviewed-by or Signed-off-by to it?

Are you asking me to add my R-b to the broken code above?

-boris

Quoted 12 lines · On Fri, Sep 25, 2020 at 04:02:58PM -0400, [email protected] wrote:

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Quoted 7 lines · Anchal Agarwal

Quoted 6 lines · Anchal Agarwal

Quoted 5 lines · On Tue, Sep 22, 2020 at 12:18:05PM -0400, [email protected] wrote:

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On 9/21/20 5:54 PM, Anchal Agarwal wrote:

Quoted 5 lines

Quoted 2 lines

Quoted 2 lines

Quoted 2 lines

Also, wrt KASLR stuff, that issue is still seen sometimes but I haven't had bandwidth to dive deep into the issue and fix it.

So what's the plan there? You first mentioned this issue early this year and judged by your response it is not clear whether you will ever spend time looking at it.

I do want to fix it and did do some debugging earlier this year just haven't gotten back to it. Also, wanted to understand if the issue is a blocker to this series?

I had some theories when debugging around this like if the random base address picked by kaslr for the resuming kernel mismatches the suspended kernel and just jogging my memory, I didn't find that as the case. Another hunch was if physical address of registered vcpu info at boot is different from what suspended kernel has and that can cause CPU's to get stuck when coming online.

The issue was only
reproducible 3% of the time out of 3000 runs hence its hard to just reproduce this.

Moreover, I also wanted to get an insight on if hibernation works correctly with KASLR generally and its only Xen causing the issue?

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Quoted 17 lines · Anchal Agarwal

Quoted 16 lines · On Fri, Sep 25, 2020 at 04:02:58PM -0400, [email protected] wrote:

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Quoted 10 lines · Anchal Agarwal

Quoted 9 lines · Anchal Agarwal

Quoted 8 lines · On Tue, Sep 22, 2020 at 12:18:05PM -0400, [email protected] wrote:

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On 9/21/20 5:54 PM, Anchal Agarwal wrote:

Also, wrt KASLR stuff, that issue is still seen sometimes but I haven't had bandwidth to dive deep into the issue and fix it.

Quoted 5 lines

Quoted 2 lines

So what's the plan there? You first mentioned this issue early this year and judged by your response it is not clear whether you will ever spend time looking at it.

I do want to fix it and did do some debugging earlier this year just haven't gotten back to it. Also, wanted to understand if the issue is a blocker to this series?

Integrating code with known bugs is less than ideal.

3% failure for this feature seems to be a manageable number from the reproducability perspective --- you should be able to script this and each iteration should take way under a minute, no?

Quoted 4 lines

I had some theories when debugging around this like if the random base address picked by kaslr for the resuming kernel mismatches the suspended kernel and just jogging my memory, I didn't find that as the case. Another hunch was if physical address of registered vcpu info at boot is different from what suspended kernel has and that can cause CPU's to get stuck when coming online.

I'd think if this were the case you'd have 100% failure rate. And we are also re-registering vcpu info on xen restore and I am not aware of any failures due to KASLR.

Quoted 6 lines

The issue was only
reproducible 3% of the time out of 3000 runs hence its hard to just reproduce this.

Moreover, I also wanted to get an insight on if hibernation works correctly with KASLR generally and its only Xen causing the issue?

With KASLR being on by default I'd be surprised if it didn't.

-boris

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Also, wrt KASLR stuff, that issue is still seen sometimes but I haven't had bandwidth to dive deep into the issue and fix it.

So what's the plan there? You first mentioned this issue early this year and judged by your response it is not clear whether you will ever spend time looking at it.

Quoted 6 lines

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I do want to fix it and did do some debugging earlier this year just haven't gotten back to it. Also, wanted to understand if the issue is a blocker to this series?

Integrating code with known bugs is less than ideal.

So for this series to be accepted, KASLR needs to be fixed along with other comments of course?

Quoted 5 lines

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I had some theories when debugging around this like if the random base address picked by kaslr for the resuming kernel mismatches the suspended kernel and just jogging my memory, I didn't find that as the case. Another hunch was if physical address of registered vcpu info at boot is different from what suspended kernel has and that can cause CPU's to get stuck when coming online.

Quoted 2 lines

I'd think if this were the case you'd have 100% failure rate. And we are also re-registering vcpu info on xen restore and I am not aware of any failures due to KASLR.

What I meant there wrt VCPU info was that VCPU info is not unregistered during hibernation, so Xen still remembers the old physical addresses for the VCPU information, created by the booting kernel. But since the hibernation kernel may have different physical addresses for VCPU info and if mismatch happens, it may cause issues with resume. During hibernation, the VCPU info register hypercall is not invoked again.

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Also, wrt KASLR stuff, that issue is still seen sometimes but I haven't had bandwidth to dive deep into the issue and fix it.

So what's the plan there? You first mentioned this issue early this year and judged by your response it is not clear whether you will ever spend time looking at it.

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I do want to fix it and did do some debugging earlier this year just haven't gotten back to it. Also, wanted to understand if the issue is a blocker to this series?

Integrating code with known bugs is less than ideal.

So for this series to be accepted, KASLR needs to be fixed along with other comments of course?

Yes, please.

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I had some theories when debugging around this like if the random base address picked by kaslr for the resuming kernel mismatches the suspended kernel and just jogging my memory, I didn't find that as the case. Another hunch was if physical address of registered vcpu info at boot is different from what suspended kernel has and that can cause CPU's to get stuck when coming online.

I'd think if this were the case you'd have 100% failure rate. And we are also re-registering vcpu info on xen restore and I am not aware of any failures due to KASLR.

Quoted 5 lines

What I meant there wrt VCPU info was that VCPU info is not unregistered during hibernation, so Xen still remembers the old physical addresses for the VCPU information, created by the booting kernel. But since the hibernation kernel may have different physical addresses for VCPU info and if mismatch happens, it may cause issues with resume. During hibernation, the VCPU info register hypercall is not invoked again.

I still don't think that's the cause but it's certainly worth having a look.

-boris

Quoted 8 lines

Quoted 5 lines

What I meant there wrt VCPU info was that VCPU info is not unregistered during hibernation, so Xen still remembers the old physical addresses for the VCPU information, created by the booting kernel. But since the hibernation kernel may have different physical addresses for VCPU info and if mismatch happens, it may cause issues with resume. During hibernation, the VCPU info register hypercall is not invoked again.

I still don't think that's the cause but it's certainly worth having a look.

Hi Boris,
Apologies for picking this up after last year.
I did some dive deep on the above statement and that is indeed the case that's happening. I did some debugging around KASLR and hibernation using reboot mode.
I observed in my debug prints that whenever vcpu_info* address for secondary vcpu assigned in xen_vcpu_setup at boot is different than what is in the image, resume gets stuck for that vcpu in bringup_cpu(). That means we have different addresses for &per_cpu(xen_vcpu_info, cpu) at boot and after control jumps into the image.

I failed to get any prints after it got stuck in bringup_cpu() and
I do not have an option to send a sysrq signal to the guest or rather get a kdump.

This change is not observed in every hibernate-resume cycle. I am not sure if this is a bug or an
expected behavior.
Also, I am contemplating the idea that it may be a bug in xen code getting triggered only when
KASLR is enabled but I do not have substantial data to prove that.
Is this a coincidence that this always happens for 1st vcpu?
Moreover, since hypervisor is not aware that guest is hibernated and it looks like a regular shutdown to dom0 during reboot mode, will re-registering vcpu_info for secondary vcpu's even plausible?

I could definitely use some advice to debug this further.

Some printk's from my debugging:

At Boot:

xen_vcpu_setup: xen_have_vcpu_info_placement=1 cpu=1, vcpup=0xffff9e548fa560e0, info.mfn=3996246 info.offset=224,

Image Loads:
It ends up in the condition:
xen_vcpu_setup()
{
...

 if (xen_hvm_domain()) {
        if (per_cpu(xen_vcpu, cpu) == &per_cpu(xen_vcpu_info, cpu))
                return 0; 

}
...
}

xen_vcpu_setup: checking mfn on resume cpu=1, info.mfn=3934806 info.offset=224, &per_cpu(xen_vcpu_info, cpu)=0xffff9d7240a560e0

This is tested on c4.2xlarge [8vcpu 15GB mem] instance with 5.10 kernel running in the guest.

Thanks,
Anchal.

Quoted 3 lines

-boris

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Quoted 17 lines · Anchal Agarwal

Quoted 8 lines

Quoted 5 lines

What I meant there wrt VCPU info was that VCPU info is not unregistered during hibernation, so Xen still remembers the old physical addresses for the VCPU information, created by the booting kernel. But since the hibernation kernel may have different physical addresses for VCPU info and if mismatch happens, it may cause issues with resume. During hibernation, the VCPU info register hypercall is not invoked again.

I still don't think that's the cause but it's certainly worth having a look.

Hi Boris,
Apologies for picking this up after last year.
I did some dive deep on the above statement and that is indeed the case that's happening. I did some debugging around KASLR and hibernation using reboot mode.
I observed in my debug prints that whenever vcpu_info* address for secondary vcpu assigned in xen_vcpu_setup at boot is different than what is in the image, resume gets stuck for that vcpu in bringup_cpu(). That means we have different addresses for &per_cpu(xen_vcpu_info, cpu) at boot and after control jumps into the image.

Quoted 2 lines

I failed to get any prints after it got stuck in bringup_cpu() and
I do not have an option to send a sysrq signal to the guest or rather get a kdump.

xenctx and xen-hvmctx might be helpful.

Quoted 7 lines

This change is not observed in every hibernate-resume cycle. I am not sure if this is a bug or an
expected behavior.
Also, I am contemplating the idea that it may be a bug in xen code getting triggered only when
KASLR is enabled but I do not have substantial data to prove that.
Is this a coincidence that this always happens for 1st vcpu?
Moreover, since hypervisor is not aware that guest is hibernated and it looks like a regular shutdown to dom0 during reboot mode, will re-registering vcpu_info for secondary vcpu's even plausible?

I think I am missing how this is supposed to work (maybe we've talked about this but it's been many months since then). You hibernate the guest and it writes the state to swap. The guest is then shut down? And what's next? How do you wake it up?

-boris

Quoted 33 lines

I could definitely use some advice to debug this further.

Some printk's from my debugging:

At Boot:

xen_vcpu_setup: xen_have_vcpu_info_placement=1 cpu=1, vcpup=0xffff9e548fa560e0, info.mfn=3996246 info.offset=224,

Image Loads:
It ends up in the condition:
xen_vcpu_setup()
{
...

 if (xen_hvm_domain()) {
        if (per_cpu(xen_vcpu, cpu) == &per_cpu(xen_vcpu_info, cpu))
                return 0;

}
...
}

xen_vcpu_setup: checking mfn on resume cpu=1, info.mfn=3934806 info.offset=224, &per_cpu(xen_vcpu_info, cpu)=0xffff9d7240a560e0

This is tested on c4.2xlarge [8vcpu 15GB mem] instance with 5.10 kernel running in the guest.

Thanks,
Anchal.

Quoted 3 lines

-boris

Quoted 35 lines · Boris Ostrovsky

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Quoted 16 lines · Anchal Agarwal

Quoted 7 lines

Quoted 5 lines

What I meant there wrt VCPU info was that VCPU info is not unregistered during hibernation, so Xen still remembers the old physical addresses for the VCPU information, created by the booting kernel. But since the hibernation kernel may have different physical addresses for VCPU info and if mismatch happens, it may cause issues with resume. During hibernation, the VCPU info register hypercall is not invoked again.

I still don't think that's the cause but it's certainly worth having a look.

Hi Boris,
Apologies for picking this up after last year.
I did some dive deep on the above statement and that is indeed the case that's happening. I did some debugging around KASLR and hibernation using reboot mode.
I observed in my debug prints that whenever vcpu_info* address for secondary vcpu assigned in xen_vcpu_setup at boot is different than what is in the image, resume gets stuck for that vcpu in bringup_cpu(). That means we have different addresses for &per_cpu(xen_vcpu_info, cpu) at boot and after control jumps into the image.

Quoted 2 lines

I failed to get any prints after it got stuck in bringup_cpu() and
I do not have an option to send a sysrq signal to the guest or rather get a kdump.

xenctx and xen-hvmctx might be helpful.

Quoted 7 lines

This change is not observed in every hibernate-resume cycle. I am not sure if this is a bug or an
expected behavior.
Also, I am contemplating the idea that it may be a bug in xen code getting triggered only when
KASLR is enabled but I do not have substantial data to prove that.
Is this a coincidence that this always happens for 1st vcpu?
Moreover, since hypervisor is not aware that guest is hibernated and it looks like a regular shutdown to dom0 during reboot mode, will re-registering vcpu_info for secondary vcpu's even plausible?

Quoted 5 lines

I think I am missing how this is supposed to work (maybe we've talked about this but it's been many months since then). You hibernate the guest and it writes the state to swap. The guest is then shut down? And what's next? How do you wake it up?

-boris

To resume a guest, guest boots up as the fresh guest and then software_resume() is called which if finds a stored hibernation image, quiesces the devices and loads the memory contents from the image. The control then transfers to the targeted kernel. This further disables non boot cpus,sycore_suspend/resume callbacks are invoked which sets up the shared_info, pvclock, grant tables etc. Since the vcpu_info pointer for each non-boot cpu is already registered, the hypercall does not happen again when bringing up the non boot cpus. This leads to inconsistencies as pointed
out earlier when KASLR is enabled.

Thanks,
Anchal

Quoted 32 lines

Quoted 32 lines

I could definitely use some advice to debug this further.

Some printk's from my debugging:

At Boot:

xen_vcpu_setup: xen_have_vcpu_info_placement=1 cpu=1, vcpup=0xffff9e548fa560e0, info.mfn=3996246 info.offset=224,

Image Loads:
It ends up in the condition:
xen_vcpu_setup()
{
...

 if (xen_hvm_domain()) {
        if (per_cpu(xen_vcpu, cpu) == &per_cpu(xen_vcpu_info, cpu))
                return 0;

}
...
}

xen_vcpu_setup: checking mfn on resume cpu=1, info.mfn=3934806 info.offset=224, &per_cpu(xen_vcpu_info, cpu)=0xffff9d7240a560e0

This is tested on c4.2xlarge [8vcpu 15GB mem] instance with 5.10 kernel running in the guest.

Thanks,
Anchal.

Quoted 3 lines

-boris

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Quoted 41 lines · Anchal Agarwal

Quoted 35 lines · Boris Ostrovsky

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Quoted 16 lines · Anchal Agarwal

Quoted 7 lines

Quoted 5 lines

What I meant there wrt VCPU info was that VCPU info is not unregistered during hibernation, so Xen still remembers the old physical addresses for the VCPU information, created by the booting kernel. But since the hibernation kernel may have different physical addresses for VCPU info and if mismatch happens, it may cause issues with resume. During hibernation, the VCPU info register hypercall is not invoked again.

I still don't think that's the cause but it's certainly worth having a look.

Hi Boris,
Apologies for picking this up after last year.
I did some dive deep on the above statement and that is indeed the case that's happening. I did some debugging around KASLR and hibernation using reboot mode.
I observed in my debug prints that whenever vcpu_info* address for secondary vcpu assigned in xen_vcpu_setup at boot is different than what is in the image, resume gets stuck for that vcpu in bringup_cpu(). That means we have different addresses for &per_cpu(xen_vcpu_info, cpu) at boot and after control jumps into the image.

Quoted 2 lines

I failed to get any prints after it got stuck in bringup_cpu() and
I do not have an option to send a sysrq signal to the guest or rather get a kdump.

xenctx and xen-hvmctx might be helpful.

Quoted 7 lines

This change is not observed in every hibernate-resume cycle. I am not sure if this is a bug or an
expected behavior.
Also, I am contemplating the idea that it may be a bug in xen code getting triggered only when
KASLR is enabled but I do not have substantial data to prove that.
Is this a coincidence that this always happens for 1st vcpu?
Moreover, since hypervisor is not aware that guest is hibernated and it looks like a regular shutdown to dom0 during reboot mode, will re-registering vcpu_info for secondary vcpu's even plausible?

Quoted 5 lines

I think I am missing how this is supposed to work (maybe we've talked about this but it's been many months since then). You hibernate the guest and it writes the state to swap. The guest is then shut down? And what's next? How do you wake it up?

-boris

Quoted 8 lines

To resume a guest, guest boots up as the fresh guest and then software_resume() is called which if finds a stored hibernation image, quiesces the devices and loads the memory contents from the image. The control then transfers to the targeted kernel. This further disables non boot cpus,sycore_suspend/resume callbacks are invoked which sets up the shared_info, pvclock, grant tables etc. Since the vcpu_info pointer for each non-boot cpu is already registered, the hypercall does not happen again when bringing up the non boot cpus. This leads to inconsistencies as pointed
out earlier when KASLR is enabled.

I'd think the 'if' condition in the code fragment below should always fail since hypervisor is creating new guest, resulting in the hypercall. Just like in the case of save/restore.

Do you call xen_vcpu_info_reset() on resume? That will re-initialize per_cpu(xen_vcpu). Maybe you need to add this to xen_syscore_resume().

-boris

Quoted 39 lines

Thanks,
Anchal

Quoted 36 lines

Quoted 36 lines

I could definitely use some advice to debug this further.

Some printk's from my debugging:

At Boot:

xen_vcpu_setup: xen_have_vcpu_info_placement=1 cpu=1, vcpup=0xffff9e548fa560e0, info.mfn=3996246 info.offset=224,

Image Loads:
It ends up in the condition:

xen_vcpu_setup()
{
...

 if (xen_hvm_domain()) {
        if (per_cpu(xen_vcpu, cpu) == &per_cpu(xen_vcpu_info, cpu))
                return 0;

}
...
}

xen_vcpu_setup: checking mfn on resume cpu=1, info.mfn=3934806 info.offset=224, &per_cpu(xen_vcpu_info, cpu)=0xffff9d7240a560e0

This is tested on c4.2xlarge [8vcpu 15GB mem] instance with 5.10 kernel running in the guest.

Thanks,
Anchal.

Quoted 3 lines

-boris

That only fails during boot but not after the control jumps into the image. The
non boot cpus are brought offline(freeze_secondary_cpus) and then online via cpu hotplug path. In that case xen_vcpu_setup doesn't invokes the hypercall again.

Another line of thought is something what kexec does to come around this problem
is to abuse soft_reset and issue it during syscore_resume or may be before the image get loaded. I haven't experimented with that yet as I am assuming there has to be a way to re-register vcpus during resume.

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Quoted 2 lines · Anchal Agarwal

That only fails during boot but not after the control jumps into the image. The
non boot cpus are brought offline(freeze_secondary_cpus) and then online via cpu hotplug path. In that case xen_vcpu_setup doesn't invokes the hypercall again.

OK, that makes sense --- by that time VCPUs have already been registered. What I don't understand though is why resume doesn't fail every time --- xen_vcpu and xen_vcpu_info should be different practically always, shouldn't they? Do you observe successful resumes when the hypercall fails?

Quoted 4 lines

Another line of thought is something what kexec does to come around this problem
is to abuse soft_reset and issue it during syscore_resume or may be before the image get loaded. I haven't experimented with that yet as I am assuming there has to be a way to re-register vcpus during resume.

Right, that sounds like it should work.

-boris

Quoted 1 line · Boris Ostrovsky

The resume won't fail because in the image the xen_vcpu and xen_vcpu_info are same. These are the same values that got in there during saving of the hibernation image. So whatever xen_vcpu got as a value during boot time registration on resume is essentially lost once the jump into the saved kernel image happens. Interesting part is if KASLR is not enabled boot time vcpup mfn is same as in the image.

Once you enable KASLR this value changes sometimes and whenever that happens resume gets stuck. Does that make sense?

No it does not resume successfully if hypercall fails because I was trying to explicitly reset vcpu and invoke hypercall.
I am just wondering why does restore logic fails to work here or probably I am missing a critical piece here.

Quoted 6 lines

Quoted 3 lines

Another line of thought is something what kexec does to come around this problem
is to abuse soft_reset and issue it during syscore_resume or may be before the image get loaded. I haven't experimented with that yet as I am assuming there has to be a way to re-register vcpus during resume.

Right, that sounds like it should work.

You mean soft reset or re-register vcpu?

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Quoted 2 lines · Anchal Agarwal

Quoted 1 line · Boris Ostrovsky

Quoted 5 lines

The resume won't fail because in the image the xen_vcpu and xen_vcpu_info are same. These are the same values that got in there during saving of the hibernation image. So whatever xen_vcpu got as a value during boot time registration on resume is essentially lost once the jump into the saved kernel image happens. Interesting part is if KASLR is not enabled boot time vcpup mfn is same as in the image.

Do you start the your guest right after you've hibernated it? What happens if you create (and keep running) a few other guests in-between? mfn would likely be different then I'd think.

Quoted 7 lines

Once you enable KASLR this value changes sometimes and whenever that happens resume gets stuck. Does that make sense?

No it does not resume successfully if hypercall fails because I was trying to explicitly reset vcpu and invoke hypercall.
I am just wondering why does restore logic fails to work here or probably I am missing a critical piece here.

If you are not using KASLR then xen_vcpu_info is at the same address every time you boot. So whatever you registered before hibernating stays the same when you boot second time and register again, and so successful comparison in xen_vcpu_setup() works. (Mostly by chance.)

But if KASLR is on then this comparison not failing should cause xen_vcpu pointer in the loaded image to become bogus because xen_vcpu is now registered for a different xen_vcpu_info address during boot.

Quoted 5 lines

Quoted 5 lines

Quoted 4 lines

Another line of thought is something what kexec does to come around this problem
is to abuse soft_reset and issue it during syscore_resume or may be before the image get loaded. I haven't experimented with that yet as I am assuming there has to be a way to re-register vcpus during resume.

Quoted 3 lines

Quoted 2 lines

Right, that sounds like it should work.

You mean soft reset or re-register vcpu?

Doing something along the lines of a soft reset. It should allow you to re-register. Not sure how you can use it without Xen changes though.

-boris

Quoted 2 lines · Boris Ostrovsky

But if KASLR is on then this comparison not failing should cause xen_vcpu pointer in the loaded image to become bogus because xen_vcpu is now registered for a different xen_vcpu_info address during boot.

The reason for that I think is once you jump into the image that information is getting lost. But there is some residue somewhere that's causing the resume to fail. I haven't been able to pinpoint the exact field value that may be causing that issue.

Correct me if I am wrong here, but even if hypothetically I put a hack to tell the kernel somehow re-register vcpu it won't pass because there is no hypercall to unregister it in first place?

Can the resumed kernel use the new values in that case [Now this is me just throwing wild guesses!!]

From: Munehisa Kamata <[email protected]>

Guest hibernation is different from xen suspend/resume/live migration. Xen save/restore does not use pm_ops as is needed by guest hibernation. Hibernation in guest follows ACPI path and is guest inititated , the hibernation image is saved within guest as compared to later modes which are xen toolstack assisted and image creation/storage is in control of hypervisor/host machine.
To differentiate between Xen suspend and PM hibernation, keep track of the on-going suspend mode by mainly using a new API to keep track of SHUTDOWN_SUSPEND state.
Introduce a simple function that keeps track of on-going suspend mode so that PM hibernation code can behave differently according to the current suspend mode.
Since Xen suspend doesn't have corresponding PM event, its main logic is modfied to acquire pm_mutex.

Though, accquirng pm_mutex is still right thing to do, we may see deadlock if PM hibernation is interrupted by Xen suspend. PM hibernation depends on xenwatch thread to process xenbus state transactions, but the thread will sleep to wait pm_mutex which is already held by PM hibernation context in the scenario. Xen shutdown code may need some changes to avoid the issue.

[Anchal Agarwal: Changelog]:
RFC v1->v2: Code refactoring
v1->v2: Remove unused functions for PM SUSPEND/PM hibernation
v2->v3: Added logic to use existing pm_notifier to detect for ARM
and abort hibernation for ARM guests. Also removed different suspend_modes and simplified the code with using existing state variables for tracking Xen suspend. The notifier won't get registered for pvh dom0 either.

Signed-off-by Anchal Agarwal <[email protected]>

Signed-off-by Munehisa Kamata <[email protected]>

From: Munehisa Kamata <[email protected]>

Since commit b3e96c0c7562 ("xen: use freeze/restore/thaw PM events for suspend/resume/chkpt"), xenbus uses PMSG_FREEZE, PMSG_THAW and PMSG_RESTORE events for Xen suspend. However, they're actually assigned to xenbus_dev_suspend(), xenbus_dev_cancel() and xenbus_dev_resume() respectively, and only suspend and resume callbacks are supported at driver level. To support PM suspend and PM hibernation, modify the bus level PM callbacks to invoke not only device driver's suspend/resume but also freeze/thaw/restore.

Note that we'll use freeze/restore callbacks even for PM suspend whereas suspend/resume callbacks are normally used in the case, becausae the existing xenbus device drivers already have suspend/resume callbacks specifically designed for Xen suspend.

So we can allow the device
drivers to keep the existing callbacks wihtout modification.

drivers/xen/xenbus/xenbus_probe.c +1 -0

@@ -599,16 +600,33 @@ int xenbus_dev_suspend(struct device *dev)
 	struct xenbus_driver *drv;
 	struct xenbus_device *xdev
 		= container_of(dev, struct xenbus_device, dev);
+	bool xen_suspend = is_xen_suspend();
 
 	DPRINTK("%s", xdev->nodename);
 
 	if (dev->driver == NULL)
 		return 0;

drivers/xen/xenbus/xenbus_probe.c +4 -0

 "%s %s failed: %d\n", xen_suspend ?
+				"suspend" : "freeze", xdev->nodename, err);
+		return err;
+	}
+
 
 

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Quoted 11 lines · Anchal Agarwal

From: Munehisa Kamata <[email protected]>

Since commit b3e96c0c7562 ("xen: use freeze/restore/thaw PM events for suspend/resume/chkpt"), xenbus uses PMSG_FREEZE, PMSG_THAW and PMSG_RESTORE events for Xen suspend. However, they're actually assigned to xenbus_dev_suspend(), xenbus_dev_cancel() and xenbus_dev_resume() respectively, and only suspend and resume callbacks are supported at driver level. To support PM suspend and PM hibernation, modify the bus level PM callbacks to invoke not only device driver's suspend/resume but also freeze/thaw/restore.

Quoted 4 lines

Note that we'll use freeze/restore callbacks even for PM suspend whereas suspend/resume callbacks are normally used in the case, becausae the existing xenbus device drivers already have suspend/resume callbacks specifically designed for Xen suspend.

Something is wrong with this sentence. Or with my brain --- I can't quite parse this.

And please be consistent with "PM suspend" vs. "PM hibernation".

Quoted 16 lines

So we can allow the device
drivers to keep the existing callbacks wihtout modification.

drivers/xen/xenbus/xenbus_probe.c +1 -0

@@ -599,16 +600,33 @@ int xenbus_dev_suspend(struct device *dev)
      struct xenbus_driver *drv;
      struct xenbus_device *xdev
              = container_of(dev, struct xenbus_device, dev);
+     bool xen_suspend = is_xen_suspend();
 
      DPRINTK("%s", xdev->nodename);
 
      if (dev->driver == NULL)
              return 0;

drivers/xen/xenbus/xenbus_probe.c int xenbus_dev_suspend(struct device *dev) · line 614

Quoted 10 lines

drivers/xen/xenbus/xenbus_probe.c +5 -4

      drv = to_xenbus_driver(dev->driver);
-     if (drv->suspend)
-             err = drv->suspend(xdev);
-     if (err)
-             dev_warn(dev, "suspend failed: %i\n", err);
+     if (xen_suspend) {
+             if (drv->suspend)
+                     err = drv->suspend(xdev);
+     } else {
+             if (drv->freeze) {

'else if' (to avoid extra indent level). In xenbus_dev_resume() too.

drivers/xen/xenbus/xenbus_probe.c int xenbus_dev_suspend(struct device *dev)

Quoted 11 lines

drivers/xen/xenbus/xenbus_probe.c +11 -0

+                     err = drv->freeze(xdev);
+                     if (!err) {
+                             free_otherend_watch(xdev);
+                             free_otherend_details(xdev);
+                             return 0;
+                     }
+             }
+     }
+
+     if (err) {
+             dev_warn(&xdev->dev,

Is there a reason why you replaced dev with xdev->dev (here and elsewhere)?

Quoted 9 lines

drivers/xen/xenbus/xenbus_probe.c +4 -0

 "%s %s failed: %d\n", xen_suspend ?
+                             "suspend" : "freeze", xdev->nodename, err);
+             return err;
+     }
+
 
 

@@ -653,8 +683,44 @@ EXPORT_SYMBOL_GPL(xenbus_dev_resume);
 

drivers/xen/xenbus/xenbus_probe.c EXPORT_SYMBOL_GPL(xenbus_dev_resume); · line 688

Quoted 7 lines

drivers/xen/xenbus/xenbus_probe.c +3 -2

 int xenbus_dev_cancel(struct device *dev)
 {
-     /* Do nothing */
-     DPRINTK("cancel");
+     int err;
+     struct xenbus_driver *drv;
+     struct xenbus_device *xendev = to_xenbus_device(dev);

xdev for consistency please.

Review EXPORT_SYMBOL_GPL(xenbus_dev_resume); · line 689

Quoted 2 lines

(quoted diff) +1 -0

+     bool xen_suspend = is_xen_suspend();

No need for this, you use it only once anyway.

-boris

From: Munehisa Kamata <[email protected]>

Add Xen PVHVM specific system core callbacks for PM hibernation support. The callbacks suspend and resume Xen primitives like shared_info, pvclock and grant table. These syscore_ops are specifically for domU hibernation. xen_suspend() calls syscore_suspend() during Xen suspend operation however, during xen suspend lock_system_sleep() lock is taken and thus system cannot trigger hibernation. These system core callbacks will be called only from the hibernation context.

Add a new quirk flag IRQCHIP_SHUTDOWN_ON_SUSPEND and add support for it the core interrupt suspend/resume paths.

Changelog:
v1->v2: Corrected the author's name to tglx@

Signed-off-by Anchal Agarwal <[email protected]>

Signed-off-by Thomas Gleixner <[email protected]>

CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.

Quoted 3 lines · Thomas Gleixner

Add a new quirk flag IRQCHIP_SHUTDOWN_ON_SUSPEND and add support for it the core interrupt suspend/resume paths.

Quoted 2 lines

Changelog:
v1->v2: Corrected the author's name to tglx@

Can you please move that Changelog part below the --- seperator next time because that's really not part of the final commit messaage and the maintainer has then to strip it off manually

Quoted 2 lines

Signed-off-by Anchal Agarwal <[email protected]>

Signed-off-by Thomas Gleixner <[email protected]>

These SOB lines are just wrongly ordered as they suggest:

Anchal has authored the patch and Thomas transported it

which is clearly not the case. So the right order is:

Signed-off-by Thomas Gleixner <[email protected]>

Signed-off-by Anchal Agarwal <[email protected]>

And that needs another tweak at the top of the change log. The first line in the mail body wants to be:

From: Thomas Gleixner <[email protected]>

followed by an empty new line before the actual changelog text starts. That way the attribution of the patch when applying it will be correct.

Documentation/process/ is there for a reason and following the few simple rules to get that straight is not rocket science.

Thanks,

tglx

From: Thomas Gleixner <[email protected]>

followed by an empty new line before the actual changelog text starts. That way the attribution of the patch when applying it will be correct.

Quoted 5 lines · Thomas Gleixner

From: Thomas Gleixner <[email protected]>

followed by an empty new line before the actual changelog text starts. That way the attribution of the patch when applying it will be correct.

The way he sent it attribution will be correct as he managed to get his MTU to send out the mail claiming to be from you.

But yes, it needs the second From line, _and_ the first from line needs to be fixed to be from him.

Save/restore xen_sched_clock_offset in syscore suspend/resume during PM hibernation. Commit '867cefb4cb1012: ("xen: Fix x86 sched_clock() interface for xen")' fixes xen guest time handling during migration. A similar issue is seen during PM hibernation when system runs CPU intensive workload. Post resume pvclock resets the value to 0 however, xen sched_clock_offset is never updated. System instability is seen during resume from hibernation when system is under heavy CPU load. Since xen_sched_clock_offset is not updated, system does not see the monotonic clock value and the scheduler would then think that heavy CPU hog tasks need more time in CPU, causing the system to freeze

Signed-off-by Anchal Agarwal <[email protected]>

---
 arch/x86/xen/suspend.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

arch/x86/xen/suspend.c +2 -1

index b12db6966af6..a62e08a11681 100644
@@ -98,8 +98,9 @@ static int xen_syscore_suspend(void)
 		return 0;
 
 	gnttab_suspend();
-
 	xen_manage_runstate_time(-1);
+	xen_save_sched_clock_offset();
+
 	xrfp.domid = DOMID_SELF;
 	xrfp.gpfn = __pa(HYPERVISOR_shared_info) >> PAGE_SHIFT;
 

arch/x86/xen/suspend.c +1 -0

+	xen_restore_sched_clock_offset();
 	xen_manage_runstate_time(0);
 	gnttab_resume();
 }

Hello,
This series fixes PM hibernation for hvm guests running on xen hypervisor. The running guest could now be hibernated and resumed successfully at a later time. The fixes for PM hibernation are added to block and network device drivers i.e xen-blkfront and xen-netfront. Any other driver that needs to add S4 support if not already, can follow same method of introducing freeze/thaw/restore callbacks.
The patches had been tested against upstream kernel and xen4.11. Large scale testing is also done on Xen based Amazon EC2 instances. All this testing involved running memory exhausting workload in the background.

Doing guest hibernation does not involve any support from hypervisor and this way guest has complete control over its state. Infrastructure restrictions for saving up guest state can be overcome by guest initiated hibernation.

These patches were send out as RFC before and all the feedback had been incorporated in the patches. The last v1 & v2 could be found here:

[v1]: https://lkml.org/lkml/2020/5/19/1312
[v2]: https://lkml.org/lkml/2020/7/2/995
All comments and feedback from v2 had been incorporated in v3 series.

Known issues:
1.KASLR causes intermittent hibernation failures. VM fails to resumes and has to be restarted. I will investigate this issue separately and shouldn't be a blocker for this patch series.
2. During hibernation, I observed sometimes that freezing of tasks fails due to busy XFS workqueuei[xfs-cil/xfs-sync]. This is also intermittent may be 1 out of 200 runs and hibernation is aborted in this case. Re-trying hibernation may work. Also, this is a known issue with hibernation and some filesystems like XFS has been discussed by the community for years with not an effectve resolution at this point.

Testing How to:
---------------
1. Setup xen hypervisor on a physical machine[ I used Ubuntu 16.04 +upstream xen-4.11]
2. Bring up a HVM guest w/t kernel compiled with hibernation patches [I used ubuntu18.04 netboot bionic images and also Amazon Linux on-prem images].
3. Create a swap file size=RAM size
4. Update grub parameters and reboot
5. Trigger pm-hibernation from within the VM

Example:
Set up a file-backed swap space. Swap file size>=Total memory on the system sudo dd if=/dev/zero of=/swap bs=$(( 1024 * 1024 )) count=4096 # 4096MiB sudo chmod 600 /swap
sudo mkswap /swap
sudo swapon /swap

Update resume device/resume offset in grub if using swap file:
resume=/dev/xvda1 resume_offset=200704 no_console_suspend=1

Execute:
--------
sudo pm-hibernate
OR
echo disk > /sys/power/state && echo reboot > /sys/power/disk

Compute resume offset code:
"
#!/usr/bin/env python
import sys
import array
import fcntl

#swap file
f = open(sys.argv[1], 'r')
buf = array.array('L', [0])

#FIBMAP
ret = fcntl.ioctl(f.fileno(), 0x01, buf)
print buf[0]
"

Aleksei Besogonov (1):
PM / hibernate: update the resume offset on SNAPSHOT_SET_SWAP_AREA

Anchal Agarwal (4):
x86/xen: Introduce new function to map HYPERVISOR_shared_info on
Resume
x86/xen: save and restore steal clock during PM hibernation
xen: Introduce wrapper for save/restore sched clock offset
xen: Update sched clock offset to avoid system instability in
hibernation

Munehisa Kamata (5):
xen/manage: keep track of the on-going suspend mode
xenbus: add freeze/thaw/restore callbacks support x86/xen: add system core suspend and resume callbacks
xen-blkfront: add callbacks for PM suspend and hibernation
xen-netfront: add callbacks for PM suspend and hibernation

Thomas Gleixner (1):
genirq: Shutdown irq chips in suspend/resume during hibernation

 arch/x86/xen/enlighten_hvm.c      |   7 +++
 arch/x86/xen/suspend.c            |  63 ++++++++++++++++++++
 arch/x86/xen/time.c               |  15 ++++-
 arch/x86/xen/xen-ops.h            |   3 +
 drivers/block/xen-blkfront.c      | 122 ++++++++++++++++++++++++++++++++++++--
 drivers/net/xen-netfront.c        |  96 +++++++++++++++++++++++++++++-
 drivers/xen/events/events_base.c  |   1 +
 drivers/xen/manage.c              |  46 ++++++++++++++
 drivers/xen/xenbus/xenbus_probe.c |  96 +++++++++++++++++++++++++-----

 include/linux/irq.h               |   2 +
 include/xen/xen-ops.h             |   3 +
 include/xen/xenbus.h              |   3 +
 kernel/irq/chip.c                 |   2 +-
 kernel/irq/internals.h            |   1 +
 kernel/irq/pm.c                   |  31 +++++++---
 kernel/power/user.c               |   7 ++-
 16 files changed, 464 insertions(+), 34 deletions(-)

Signature · 1 line

2.16.6

Quoted 115 lines · Anchal Agarwal

Hello,
This series fixes PM hibernation for hvm guests running on xen hypervisor. The running guest could now be hibernated and resumed successfully at a later time. The fixes for PM hibernation are added to block and network device drivers i.e xen-blkfront and xen-netfront. Any other driver that needs to add S4 support if not already, can follow same method of introducing freeze/thaw/restore callbacks.
The patches had been tested against upstream kernel and xen4.11. Large scale testing is also done on Xen based Amazon EC2 instances. All this testing involved running memory exhausting workload in the background.

Doing guest hibernation does not involve any support from hypervisor and this way guest has complete control over its state. Infrastructure restrictions for saving up guest state can be overcome by guest initiated hibernation.

These patches were send out as RFC before and all the feedback had been incorporated in the patches. The last v1 & v2 could be found here:

[v1]: https://lkml.org/lkml/2020/5/19/1312
[v2]: https://lkml.org/lkml/2020/7/2/995
All comments and feedback from v2 had been incorporated in v3 series.

Known issues:
1.KASLR causes intermittent hibernation failures. VM fails to resumes and has to be restarted. I will investigate this issue separately and shouldn't be a blocker for this patch series.
2. During hibernation, I observed sometimes that freezing of tasks fails due to busy XFS workqueuei[xfs-cil/xfs-sync]. This is also intermittent may be 1 out of 200 runs and hibernation is aborted in this case. Re-trying hibernation may work. Also, this is a known issue with hibernation and some filesystems like XFS has been discussed by the community for years with not an effectve resolution at this point.

Testing How to:
---------------
1. Setup xen hypervisor on a physical machine[ I used Ubuntu 16.04 +upstream xen-4.11]
2. Bring up a HVM guest w/t kernel compiled with hibernation patches [I used ubuntu18.04 netboot bionic images and also Amazon Linux on-prem images].
3. Create a swap file size=RAM size
4. Update grub parameters and reboot
5. Trigger pm-hibernation from within the VM

Example:
Set up a file-backed swap space. Swap file size>=Total memory on the system sudo dd if=/dev/zero of=/swap bs=$(( 1024 * 1024 )) count=4096 # 4096MiB sudo chmod 600 /swap
sudo mkswap /swap
sudo swapon /swap

Update resume device/resume offset in grub if using swap file:
resume=/dev/xvda1 resume_offset=200704 no_console_suspend=1

Execute:
--------
sudo pm-hibernate
OR
echo disk > /sys/power/state && echo reboot > /sys/power/disk

Compute resume offset code:
"
#!/usr/bin/env python
import sys
import array
import fcntl

#swap file
f = open(sys.argv[1], 'r')
buf = array.array('L', [0])

#FIBMAP
ret = fcntl.ioctl(f.fileno(), 0x01, buf)
print buf[0]
"

Aleksei Besogonov (1):
PM / hibernate: update the resume offset on SNAPSHOT_SET_SWAP_AREA

Anchal Agarwal (4):
x86/xen: Introduce new function to map HYPERVISOR_shared_info on
Resume
x86/xen: save and restore steal clock during PM hibernation
xen: Introduce wrapper for save/restore sched clock offset
xen: Update sched clock offset to avoid system instability in
hibernation

Munehisa Kamata (5):
xen/manage: keep track of the on-going suspend mode
xenbus: add freeze/thaw/restore callbacks support x86/xen: add system core suspend and resume callbacks
xen-blkfront: add callbacks for PM suspend and hibernation
xen-netfront: add callbacks for PM suspend and hibernation

Thomas Gleixner (1):
genirq: Shutdown irq chips in suspend/resume during hibernation

 arch/x86/xen/enlighten_hvm.c      |   7 +++
 arch/x86/xen/suspend.c            |  63 ++++++++++++++++++++
 arch/x86/xen/time.c               |  15 ++++-
 arch/x86/xen/xen-ops.h            |   3 +
 drivers/block/xen-blkfront.c      | 122 ++++++++++++++++++++++++++++++++++++--
 drivers/net/xen-netfront.c        |  96 +++++++++++++++++++++++++++++-
 drivers/xen/events/events_base.c  |   1 +
 drivers/xen/manage.c              |  46 ++++++++++++++
 drivers/xen/xenbus/xenbus_probe.c |  96 +++++++++++++++++++++++++-----
 include/linux/irq.h               |   2 +
 include/xen/xen-ops.h             |   3 +
 include/xen/xenbus.h              |   3 +
 kernel/irq/chip.c                 |   2 +-
 kernel/irq/internals.h            |   1 +
 kernel/irq/pm.c                   |  31 +++++++---
 kernel/power/user.c               |   7 ++-
 16 files changed, 464 insertions(+), 34 deletions(-)

Quoted 3 lines

--
2.16.6

A gentle ping on the series in case there is any more feedback or can we plan to merge this? I can then send the series with minor fixes pointed by tglx@

CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.

Quoted 117 lines · Anchal Agarwal

Quoted 115 lines · Anchal Agarwal

Hello,
This series fixes PM hibernation for hvm guests running on xen hypervisor. The running guest could now be hibernated and resumed successfully at a later time. The fixes for PM hibernation are added to block and network device drivers i.e xen-blkfront and xen-netfront. Any other driver that needs to add S4 support if not already, can follow same method of introducing freeze/thaw/restore callbacks.
The patches had been tested against upstream kernel and xen4.11. Large scale testing is also done on Xen based Amazon EC2 instances. All this testing involved running memory exhausting workload in the background.

Doing guest hibernation does not involve any support from hypervisor and this way guest has complete control over its state. Infrastructure restrictions for saving up guest state can be overcome by guest initiated hibernation.

These patches were send out as RFC before and all the feedback had been incorporated in the patches. The last v1 & v2 could be found here:

[v1]: https://lkml.org/lkml/2020/5/19/1312
[v2]: https://lkml.org/lkml/2020/7/2/995
All comments and feedback from v2 had been incorporated in v3 series.

Known issues:
1.KASLR causes intermittent hibernation failures. VM fails to resumes and has to be restarted. I will investigate this issue separately and shouldn't be a blocker for this patch series.
2. During hibernation, I observed sometimes that freezing of tasks fails due to busy XFS workqueuei[xfs-cil/xfs-sync]. This is also intermittent may be 1 out of 200 runs and hibernation is aborted in this case. Re-trying hibernation may work. Also, this is a known issue with hibernation and some filesystems like XFS has been discussed by the community for years with not an effectve resolution at this point.

Testing How to:
---------------
1. Setup xen hypervisor on a physical machine[ I used Ubuntu 16.04 +upstream xen-4.11]
2. Bring up a HVM guest w/t kernel compiled with hibernation patches [I used ubuntu18.04 netboot bionic images and also Amazon Linux on-prem images].
3. Create a swap file size=RAM size
4. Update grub parameters and reboot
5. Trigger pm-hibernation from within the VM

Example:
Set up a file-backed swap space. Swap file size>=Total memory on the system sudo dd if=/dev/zero of=/swap bs=$(( 1024 * 1024 )) count=4096 # 4096MiB sudo chmod 600 /swap
sudo mkswap /swap
sudo swapon /swap

Update resume device/resume offset in grub if using swap file:
resume=/dev/xvda1 resume_offset=200704 no_console_suspend=1

Execute:
--------
sudo pm-hibernate
OR
echo disk > /sys/power/state && echo reboot > /sys/power/disk

Compute resume offset code:
"
#!/usr/bin/env python
import sys
import array
import fcntl

#swap file
f = open(sys.argv[1], 'r')
buf = array.array('L', [0])

#FIBMAP
ret = fcntl.ioctl(f.fileno(), 0x01, buf)
print buf[0]
"

Aleksei Besogonov (1):
PM / hibernate: update the resume offset on SNAPSHOT_SET_SWAP_AREA

Anchal Agarwal (4):
x86/xen: Introduce new function to map HYPERVISOR_shared_info on
Resume
x86/xen: save and restore steal clock during PM hibernation
xen: Introduce wrapper for save/restore sched clock offset
xen: Update sched clock offset to avoid system instability in
hibernation

Munehisa Kamata (5):
xen/manage: keep track of the on-going suspend mode
xenbus: add freeze/thaw/restore callbacks support x86/xen: add system core suspend and resume callbacks
xen-blkfront: add callbacks for PM suspend and hibernation
xen-netfront: add callbacks for PM suspend and hibernation

Thomas Gleixner (1):
genirq: Shutdown irq chips in suspend/resume during hibernation

 arch/x86/xen/enlighten_hvm.c      |   7 +++
 arch/x86/xen/suspend.c            |  63 ++++++++++++++++++++
 arch/x86/xen/time.c               |  15 ++++-
 arch/x86/xen/xen-ops.h            |   3 +
 drivers/block/xen-blkfront.c      | 122 ++++++++++++++++++++++++++++++++++++--
 drivers/net/xen-netfront.c        |  96 +++++++++++++++++++++++++++++-
 drivers/xen/events/events_base.c  |   1 +
 drivers/xen/manage.c              |  46 ++++++++++++++
 drivers/xen/xenbus/xenbus_probe.c |  96 +++++++++++++++++++++++++-----
 include/linux/irq.h               |   2 +
 include/xen/xen-ops.h             |   3 +
 include/xen/xenbus.h              |   3 +
 kernel/irq/chip.c                 |   2 +-
 kernel/irq/internals.h            |   1 +
 kernel/irq/pm.c                   |  31 +++++++---
 kernel/power/user.c               |   7 ++-
 16 files changed, 464 insertions(+), 34 deletions(-)

Quoted 5 lines

Quoted 3 lines

--
2.16.6

A gentle ping on the series in case there is any more feedback or can we plan to merge this? I can then send the series with minor fixes pointed by tglx@

Some more time, please!

Quoted 128 lines · Rafael J. Wysocki

CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.

Quoted 122 lines · Anchal Agarwal

Quoted 115 lines · Anchal Agarwal

Hello,
This series fixes PM hibernation for hvm guests running on xen hypervisor. The running guest could now be hibernated and resumed successfully at a later time. The fixes for PM hibernation are added to block and network device drivers i.e xen-blkfront and xen-netfront. Any other driver that needs to add S4 support if not already, can follow same method of introducing freeze/thaw/restore callbacks.
The patches had been tested against upstream kernel and xen4.11. Large scale testing is also done on Xen based Amazon EC2 instances. All this testing involved running memory exhausting workload in the background.

Doing guest hibernation does not involve any support from hypervisor and this way guest has complete control over its state. Infrastructure restrictions for saving up guest state can be overcome by guest initiated hibernation.

These patches were send out as RFC before and all the feedback had been incorporated in the patches. The last v1 & v2 could be found here:

[v1]: https://lkml.org/lkml/2020/5/19/1312
[v2]: https://lkml.org/lkml/2020/7/2/995
All comments and feedback from v2 had been incorporated in v3 series.

Known issues:
1.KASLR causes intermittent hibernation failures. VM fails to resumes and has to be restarted. I will investigate this issue separately and shouldn't be a blocker for this patch series.
2. During hibernation, I observed sometimes that freezing of tasks fails due to busy XFS workqueuei[xfs-cil/xfs-sync]. This is also intermittent may be 1 out of 200 runs and hibernation is aborted in this case. Re-trying hibernation may work. Also, this is a known issue with hibernation and some filesystems like XFS has been discussed by the community for years with not an effectve resolution at this point.

Testing How to:
---------------
1. Setup xen hypervisor on a physical machine[ I used Ubuntu 16.04 +upstream xen-4.11]
2. Bring up a HVM guest w/t kernel compiled with hibernation patches [I used ubuntu18.04 netboot bionic images and also Amazon Linux on-prem images].
3. Create a swap file size=RAM size
4. Update grub parameters and reboot
5. Trigger pm-hibernation from within the VM

Example:
Set up a file-backed swap space. Swap file size>=Total memory on the system sudo dd if=/dev/zero of=/swap bs=$(( 1024 * 1024 )) count=4096 # 4096MiB sudo chmod 600 /swap
sudo mkswap /swap
sudo swapon /swap

Update resume device/resume offset in grub if using swap file:
resume=/dev/xvda1 resume_offset=200704 no_console_suspend=1

Execute:
--------
sudo pm-hibernate
OR
echo disk > /sys/power/state && echo reboot > /sys/power/disk

Compute resume offset code:
"
#!/usr/bin/env python
import sys
import array
import fcntl

#swap file
f = open(sys.argv[1], 'r')
buf = array.array('L', [0])

#FIBMAP
ret = fcntl.ioctl(f.fileno(), 0x01, buf)
print buf[0]
"

Aleksei Besogonov (1):
PM / hibernate: update the resume offset on SNAPSHOT_SET_SWAP_AREA

Anchal Agarwal (4):
x86/xen: Introduce new function to map HYPERVISOR_shared_info on
Resume
x86/xen: save and restore steal clock during PM hibernation
xen: Introduce wrapper for save/restore sched clock offset
xen: Update sched clock offset to avoid system instability in
hibernation

Munehisa Kamata (5):
xen/manage: keep track of the on-going suspend mode
xenbus: add freeze/thaw/restore callbacks support x86/xen: add system core suspend and resume callbacks
xen-blkfront: add callbacks for PM suspend and hibernation
xen-netfront: add callbacks for PM suspend and hibernation

Thomas Gleixner (1):
genirq: Shutdown irq chips in suspend/resume during hibernation

 arch/x86/xen/enlighten_hvm.c      |   7 +++
 arch/x86/xen/suspend.c            |  63 ++++++++++++++++++++
 arch/x86/xen/time.c               |  15 ++++-
 arch/x86/xen/xen-ops.h            |   3 +
 drivers/block/xen-blkfront.c      | 122 ++++++++++++++++++++++++++++++++++++--
 drivers/net/xen-netfront.c        |  96 +++++++++++++++++++++++++++++-
 drivers/xen/events/events_base.c  |   1 +
 drivers/xen/manage.c              |  46 ++++++++++++++
 drivers/xen/xenbus/xenbus_probe.c |  96 +++++++++++++++++++++++++-----
 include/linux/irq.h               |   2 +
 include/xen/xen-ops.h             |   3 +
 include/xen/xenbus.h              |   3 +
 kernel/irq/chip.c                 |   2 +-
 kernel/irq/internals.h            |   1 +
 kernel/irq/pm.c                   |  31 +++++++---
 kernel/power/user.c               |   7 ++-
 16 files changed, 464 insertions(+), 34 deletions(-)

Quoted 3 lines

--
2.16.6

A gentle ping on the series in case there is any more feedback or can we plan to merge this? I can then send the series with minor fixes pointed by tglx@

Quoted 2 lines

Some more time, please!

Sure happy to answer any more questions and fix more BUGS!!

--
Anchal

Known issues:
1.KASLR causes intermittent hibernation failures. VM fails to resumes and has to be restarted. I will investigate this issue separately and shouldn't be a blocker for this patch series.

2. During hibernation, I observed sometimes that freezing of tasks fails due to busy XFS workqueuei[xfs-cil/xfs-sync]. This is also intermittent may be 1 out of 200 runs and hibernation is aborted in this case. Re-trying hibernation may work. Also, this is a known issue with hibernation and some filesystems like XFS has been discussed by the community for years with not an effectve resolution at this point.