kvm: RDTSCP on AMD

PATCH In review Borislav Petkov 4 participants 18 messages Dec 10, 2018 – Dec 20, 2018 KVM

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Borislav Petkov

author

2018-12-10 18:13 UTC #0 lore raw

Reviving an old thread here.

Quoted 8 lines · Paolo Bonzini

Quoted 7 lines · Eduardo Habkost
Quoted 4 lines
Quoted 4 lines
Nothing is needed in the kernel actually. You can skip the intercept by running the guest with MSR_TSC_AUX set to the guest's expected value.
Which KVM does, except that it's botched so I need to apply the
patch in https://lkml.org/lkml/2016/4/13/802.
Do you mean -cpu Opteron_G*,+rdtscp will be buggy on Linux v4.5? (v4.5 reports rdtscp as supported in GET_SUPPORTED_CPUID)

Quoted 8 lines

Quoted 3 lines
Can we do something to make QEMU detect the buggy kernel before allowing rdtscp to be enabled, or should we just tell people to upgrade their kernel?
We usually just tell people to use the latest stable kernel.
Adding new CPU models is not a big deal, in fact it's almost easier than getting compat properties right. :)

Ok, can we finally revert

33b5e8c03ae7 ("target-i386: Disable rdtscp on Opteron_G* CPU models")

in the qemu tree?

Three years should be enough by now for

46896c73c1a4 ("KVM: svm: add support for RDTSCP")

to have percolated downstream.

Btw, its commit message talks about Linux not using RDTSCP but that will change soon. :-)

Oh, and the EPYC qemu CPU model has CPUID_EXT2_RDTSCP and works just fine when patching in RDTSCP:

[    0.543197] apply_alternatives: feat: 3*32+18, old: (read_tsc+0x0/0x10 (ffffffff8101d1c0) len: 5), repl: (ffffffff824e6d33, len: 5), pad: 3
[    0.544448] ffffffff8101d1c0: old_insn: 0f 31 90 90 90
[    0.545023] ffffffff824e6d33: rpl_insn: 0f ae e8 0f 31
[    0.545598] ffffffff8101d1c0: final_insn: 0f ae e8 0f 31
[    0.546193] apply_alternatives: feat: 1*32+27, old: (read_tsc+0x0/0x10 (ffffffff8101d1c0) len: 5), repl: (ffffffff824e6d38, len: 3), pad: 3
[    0.547195] ffffffff8101d1c0: old_insn: 0f ae e8 0f 31
[    0.547775] ffffffff824e6d38: rpl_insn: 0f 01 f9
[    0.548307] ffffffff8101d1c0: final_insn: 0f 01 f9 66 90

That final_insn which gets patched to by the alternatives is

ffffffff8101d1c0:       0f 01 f9                rdtscp
ffffffff8101d1c3:       66 90                   xchg %ax,%ax

Thx.

Signature · 4 lines

Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Eduardo Habkost

2018-12-10 18:37 UTC #1 lore raw

Quoted 24 lines · Borislav Petkov

Reviving an old thread here.
Quoted 8 lines · Paolo Bonzini
Quoted 7 lines · Eduardo Habkost
Quoted 4 lines
Quoted 4 lines
Nothing is needed in the kernel actually. You can skip the intercept by running the guest with MSR_TSC_AUX set to the guest's expected value.
Which KVM does, except that it's botched so I need to apply the
patch in https://lkml.org/lkml/2016/4/13/802.
Do you mean -cpu Opteron_G*,+rdtscp will be buggy on Linux v4.5? (v4.5 reports rdtscp as supported in GET_SUPPORTED_CPUID)
Quoted 8 lines
Quoted 3 lines
Can we do something to make QEMU detect the buggy kernel before allowing rdtscp to be enabled, or should we just tell people to upgrade their kernel?
We usually just tell people to use the latest stable kernel.
Adding new CPU models is not a big deal, in fact it's almost easier than getting compat properties right. :)
Ok, can we finally revert
33b5e8c03ae7 ("target-i386: Disable rdtscp on Opteron_G* CPU models")

Quoted 7 lines

in the qemu tree?
Three years should be enough by now for
46896c73c1a4 ("KVM: svm: add support for RDTSCP")
to have percolated downstream.

That's Linux v4.5, released in March 2016.

It isn't as simply as reverting commit 33b5e8c03ae7, but we can surely re-add RDTSCP on pc-*-4.0 and newer.

I thought we added documentation mentioning the minimum kernel version required by QEMU, but I can't find it. In either case, it seems reasonable to require Linux 4.5 or newer on newer machine-types.

Signature · 1 line

Eduardo

Borislav Petkov

author

2018-12-10 18:41 UTC #2 lore raw

Quoted 2 lines · Eduardo Habkost

It isn't as simply as reverting commit 33b5e8c03ae7, but we can surely re-add RDTSCP on pc-*-4.0 and newer.

Sure. If you could only point me to an example how to add that to pc-*-4.0 and newer, I'll gladly cook up a patch and test it.

Quoted 4 lines

I thought we added documentation mentioning the minimum kernel version required by QEMU, but I can't find it. In either case, it seems reasonable to require Linux 4.5 or newer on newer machine-types.

When you say "require" does that mean, one puts it in a text file somewhere in the qemu sources or do we enforce it somehow?

Thx.

Signature · 4 lines

Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Eduardo Habkost

2018-12-10 19:06 UTC #3 lore raw

Quoted 7 lines · Borislav Petkov

Quoted 2 lines · Eduardo Habkost
It isn't as simply as reverting commit 33b5e8c03ae7, but we can surely re-add RDTSCP on pc-*-4.0 and newer.
Sure. If you could only point me to an example how to add that to pc-*-4.0 and newer, I'll gladly cook up a patch and test it.

Quoted 7 lines

Quoted 4 lines
I thought we added documentation mentioning the minimum kernel version required by QEMU, but I can't find it. In either case, it seems reasonable to require Linux 4.5 or newer on newer machine-types.
When you say "require" does that mean, one puts it in a text file somewhere in the qemu sources or do we enforce it somehow?

I mean documenting it. We already have code that will print warnings if a feature isn't available.

See my previous attempt to document the minimum kernel version at <https://www.mail-archive.com/[email protected]/msg486559.html>.

Signature · 1 line

Eduardo

Borislav Petkov

author

2018-12-10 19:42 UTC #4 lore raw

Quoted 5 lines · Eduardo Habkost

I mean documenting it. We already have code that will print warnings if a feature isn't available.
See my previous attempt to document the minimum kernel version at <https://www.mail-archive.com/[email protected]/msg486559.html>.

Something like this?

I still have no clue how to add RDTSCP on pc-*-4.0 and newer.

Thx.

---

qemu-doc.texi +8 -0

index f7ad1dfe4b69..913b2ef68d54 100644
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::

@@ -2813,6 +2814,13 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.
 @end table
 
+@node System requirements
+@chapter System requirements
+
+@section KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.
 
 @include qemu-tech.texi

target/i386/cpu.c +4 -7

index f81d35e1f914..34bb5b74136d 100644
@@ -2706,7 +2706,6 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_DE | CPUID_FP87,
         .features[FEAT_1_ECX] =
             CPUID_EXT_CX16 | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
         .features[FEAT_8000_0001_ECX] =

@@ -2730,9 +2729,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
         .features[FEAT_1_ECX] =
             CPUID_EXT_POPCNT | CPUID_EXT_CX16 | CPUID_EXT_MONITOR |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL |
+	    CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_MISALIGNSSE | CPUID_EXT3_SSE4A |
             CPUID_EXT3_ABM | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM,

@@ -2757,10 +2756,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_POPCNT | CPUID_EXT_SSE42 | CPUID_EXT_SSE41 |
             CPUID_EXT_CX16 | CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

@@ -2788,10 +2786,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_AES | CPUID_EXT_POPCNT | CPUID_EXT_SSE42 |
             CPUID_EXT_SSE41 | CPUID_EXT_CX16 | CPUID_EXT_FMA |
             CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_TBM | CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

Signature · 4 lines

Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Eduardo Habkost

2018-12-10 20:08 UTC #5 lore raw

Quoted 10 lines · Borislav Petkov

Quoted 5 lines · Eduardo Habkost
I mean documenting it. We already have code that will print warnings if a feature isn't available.
See my previous attempt to document the minimum kernel version at <https://www.mail-archive.com/[email protected]/msg486559.html>.
Something like this?
I still have no clue how to add RDTSCP on pc-*-4.0 and newer.

qemu.git master have no PC_COMPAT_3_1 and pc-*-4.0 machine-types yet. I've sent another reply with additional pointers.

Quoted 18 lines

Thx.

---

qemu-doc.texi +1 -0

index f7ad1dfe4b69..913b2ef68d54 100644
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::

@@ -2813,6 +2814,13 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.

qemu-doc.texi Act as if the host page size was 'pagesize' bytes · line 2824

Quoted 10 lines

qemu-doc.texi +7 -0

 @end table
 
+@node System requirements
+@chapter System requirements
+
+@section KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.

Sounds good, but it would be nice to document what exactly makes Linux 4.5+ necessary. e.g.:

| On x86_64 hosts, it is recommended to run Linux 4.5 or newer on
| the host when using the KVM accelerator.
| 
| The Opteron_G2, OpteronG3, Opteron_G4, and Opteron_G5 CPU
| models require KVM support for RDTSCP, which was added on
| Linux 4.5.

I'm CCing some people who may help review English grammar and style.

Signature · 1 line

Eduardo

Borislav Petkov

author

2018-12-10 20:39 UTC #6 lore raw

Quoted 3 lines · Eduardo Habkost

| The Opteron_G2, OpteronG3, Opteron_G4, and Opteron_G5 CPU
| models require KVM support for RDTSCP, which was added on
| Linux 4.5.

I've added that to the current diff:

"The OpteronG[345] CPU models require KVM support for RDTSCP, which was added with Linux 4.5."

In the meantime, I tried executing RDTSCP on a K8 laptop and it gave SIGILL so I'd say the AMD docs have a typo and family 0xf - at least the A-E revisions of which model 6 is a part of - doesn't have RDTSCP.

But let's see...

Thx.

Signature · 4 lines

Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Daniel P. Berrangé

2018-12-11 10:38 UTC #7 lore raw

In reply to Eduardo Habkost

Quoted 54 lines · Eduardo Habkost

Quoted 10 lines · Borislav Petkov
Quoted 5 lines · Eduardo Habkost
I mean documenting it. We already have code that will print warnings if a feature isn't available.
See my previous attempt to document the minimum kernel version at <https://www.mail-archive.com/[email protected]/msg486559.html>.
Something like this?
I still have no clue how to add RDTSCP on pc-*-4.0 and newer.
qemu.git master have no PC_COMPAT_3_1 and pc-*-4.0 machine-types yet. I've sent another reply with additional pointers.
Quoted 18 lines
Thx.
---
qemu-doc.texi +1 -0
index f7ad1dfe4b69..913b2ef68d54 100644
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::
@@ -2813,6 +2814,13 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.
qemu-doc.texi Act as if the host page size was 'pagesize' bytes · line 2824
Quoted 10 lines
qemu-doc.texi +7 -0
 @end table
 
+@node System requirements
+@chapter System requirements
+
+@section KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.
 
Sounds good, but it would be nice to document what exactly makes Linux 4.5+ necessary. e.g.:
| On x86_64 hosts, it is recommended to run Linux 4.5 or newer on
| the host when using the KVM accelerator.
| 
| The Opteron_G2, OpteronG3, Opteron_G4, and Opteron_G5 CPU
| models require KVM support for RDTSCP, which was added on
| Linux 4.5.

Quoted 2 lines

I'm CCing some people who may help review English grammar and style.

Note that QEMU has a declared supported platform list which is used to set the minimum software versions required.

https://qemu.weilnetz.de/doc/qemu-doc.html#Linux-OS

Based on that policy, the Linux distros we aim to support have the following kernel versions:

- Debian Jessie: 4.5
- Debian Stretch: 4.5
- RHEL-7: 3.10
- Ubuntu LTS (Xenial): 4.5
- OpenSUSE Leap 15: 4.12.14

So we can't require Linux 4.5 as a minimum version at this time.

Regards,
Daniel

Signature · 3 lines

|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

Eduardo Habkost

2018-12-11 11:55 UTC #8 lore raw

Quoted 66 lines · Daniel P. Berrangé

Quoted 54 lines · Eduardo Habkost
Quoted 10 lines · Borislav Petkov
Quoted 5 lines · Eduardo Habkost
I mean documenting it. We already have code that will print warnings if a feature isn't available.
See my previous attempt to document the minimum kernel version at <https://www.mail-archive.com/[email protected]/msg486559.html>.
Something like this?
I still have no clue how to add RDTSCP on pc-*-4.0 and newer.
qemu.git master have no PC_COMPAT_3_1 and pc-*-4.0 machine-types yet. I've sent another reply with additional pointers.
Quoted 18 lines
Thx.
---
qemu-doc.texi +1 -0
index f7ad1dfe4b69..913b2ef68d54 100644
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::
@@ -2813,6 +2814,13 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.
qemu-doc.texi Act as if the host page size was 'pagesize' bytes · line 2824
Quoted 10 lines
qemu-doc.texi +7 -0
 @end table
 
+@node System requirements
+@chapter System requirements
+
+@section KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.
 
Sounds good, but it would be nice to document what exactly makes Linux 4.5+ necessary. e.g.:
| On x86_64 hosts, it is recommended to run Linux 4.5 or newer on
| the host when using the KVM accelerator.
| 
| The Opteron_G2, OpteronG3, Opteron_G4, and Opteron_G5 CPU
| models require KVM support for RDTSCP, which was added on
| Linux 4.5.
Quoted 2 lines
I'm CCing some people who may help review English grammar and style.
Note that QEMU has a declared supported platform list which is used to set the minimum software versions required.
https://qemu.weilnetz.de/doc/qemu-doc.html#Linux-OS
Based on that policy, the Linux distros we aim to support have the following kernel versions:

Quoted 7 lines

- Debian Jessie: 4.5
- Debian Stretch: 4.5
- RHEL-7: 3.10
- Ubuntu LTS (Xenial): 4.5
- OpenSUSE Leap 15: 4.12.14
So we can't require Linux 4.5 as a minimum version at this time.

I'd like us to take a step back and consider what exactly "support" means here. QEMU will still work on older kernels if we add RDTSCP to the CPU models, but at the same time I would like to document that our strict runnability guarantees may not be kept if running Linux < 4.5.

Signature · 1 line

Eduardo

Daniel P. Berrangé

2018-12-11 14:35 UTC #9 lore raw

Quoted 73 lines · Eduardo Habkost

Quoted 72 lines · Daniel P. Berrangé
Quoted 54 lines · Eduardo Habkost
Quoted 10 lines · Borislav Petkov
Quoted 5 lines · Eduardo Habkost
I mean documenting it. We already have code that will print warnings if a feature isn't available.
See my previous attempt to document the minimum kernel version at <https://www.mail-archive.com/[email protected]/msg486559.html>.
Something like this?
I still have no clue how to add RDTSCP on pc-*-4.0 and newer.
qemu.git master have no PC_COMPAT_3_1 and pc-*-4.0 machine-types yet. I've sent another reply with additional pointers.
Quoted 18 lines
Thx.
---
qemu-doc.texi +1 -0
index f7ad1dfe4b69..913b2ef68d54 100644
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::
@@ -2813,6 +2814,13 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.
qemu-doc.texi Act as if the host page size was 'pagesize' bytes · line 2824
Quoted 10 lines
qemu-doc.texi +7 -0
 @end table
 
+@node System requirements
+@chapter System requirements
+
+@section KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.
 
Sounds good, but it would be nice to document what exactly makes Linux 4.5+ necessary. e.g.:
| On x86_64 hosts, it is recommended to run Linux 4.5 or newer on
| the host when using the KVM accelerator.
| 
| The Opteron_G2, OpteronG3, Opteron_G4, and Opteron_G5 CPU
| models require KVM support for RDTSCP, which was added on
| Linux 4.5.
Quoted 2 lines
I'm CCing some people who may help review English grammar and style.
Note that QEMU has a declared supported platform list which is used to set the minimum software versions required.
https://qemu.weilnetz.de/doc/qemu-doc.html#Linux-OS
Based on that policy, the Linux distros we aim to support have the following kernel versions:
- Debian Jessie: 4.5
- Debian Stretch: 4.5
- RHEL-7: 3.10
- Ubuntu LTS (Xenial): 4.5
- OpenSUSE Leap 15: 4.12.14

Quoted 7 lines

Quoted 1 line
So we can't require Linux 4.5 as a minimum version at this time.
I'd like us to take a step back and consider what exactly "support" means here. QEMU will still work on older kernels if we add RDTSCP to the CPU models, but at the same time I would like to document that our strict runnability guarantees may not be kept if running Linux < 4.5.

I've just noticed that this thread is not in fact on qemu-devel. So rather than debating the meaning of support here, lets discuss it once the patch adding rdtscp to OpteronG* CPU model is posted to qemu-devel.

Regards,
Daniel

Signature · 3 lines

|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

Paolo Bonzini

maintainer

2018-12-11 15:23 UTC #10 lore raw

In reply to Eduardo Habkost

Quoted 6 lines · Eduardo Habkost

Quoted 6 lines
- Debian Jessie: 4.5
- Debian Stretch: 4.5
- RHEL-7: 3.10
- Ubuntu LTS (Xenial): 4.5
- OpenSUSE Leap 15: 4.12.14

Quoted 6 lines

Quoted 1 line
So we can't require Linux 4.5 as a minimum version at this time.
I'd like us to take a step back and consider what exactly "support" means here. QEMU will still work on older kernels if we add RDTSCP to the CPU models, but at the same time I would like to document that our strict runnability guarantees may not be kept if running Linux < 4.5.

Anyway RHEL does have RDTSC support for AMD, and a bunch of other stuff.
The frankenkernel's KVM is somewhere between 4.5 and 4.10, with a dash
of 4.20 of course. :)

Paolo

Daniel P. Berrangé

2018-12-11 15:30 UTC #11 lore raw

Quoted 14 lines · Paolo Bonzini

Quoted 6 lines · Eduardo Habkost
Quoted 6 lines
- Debian Jessie: 4.5
- Debian Stretch: 4.5
- RHEL-7: 3.10
- Ubuntu LTS (Xenial): 4.5
- OpenSUSE Leap 15: 4.12.14
Quoted 6 lines
Quoted 1 line
So we can't require Linux 4.5 as a minimum version at this time.
I'd like us to take a step back and consider what exactly "support" means here. QEMU will still work on older kernels if we add RDTSCP to the CPU models, but at the same time I would like to document that our strict runnability guarantees may not be kept if running Linux < 4.5.

Quoted 3 lines

Anyway RHEL does have RDTSC support for AMD, and a bunch of other stuff.
The frankenkernel's KVM is somewhere between 4.5 and 4.10, with a dash
of 4.20 of course. :)

Great, then, this is a non-issue - we just need to mention that fact in the commit that sets the min version for the kernel

Regards,
Daniel

Signature · 3 lines

|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

Borislav Petkov

author

2018-12-11 16:14 UTC #12 lore raw

PATCH 1/1 target-i386: Reenable RDTSCP support on Opteron_G[345] CPU models

+ qemu-devel.

Quoted 2 lines · Daniel P. Berrangé

Great, then, this is a non-issue - we just need to mention that fact in the commit that sets the min version for the kernel

Ok, here's a first draft ontop of Eduardo's machine-next branch from
http://github.com/ehabkost/qemu

Also, thanks for the help Eduardo! :-)

---
From: Borislav Petkov <[email protected]>
Date: Tue, 11 Dec 2018 17:01:00 +0100

The missing functionality was added ~3 years ago with the Linux commit

46896c73c1a4 ("KVM: svm: add support for RDTSCP")

so reenable RDTSCP support on those CPU models.

Opteron_G2 - being family 15, model 6, doesn't have RDTSCP support (the real hardware doesn't have it. K8 got RDTSCP support with the NPT models, i.e., models >= 0x40).

Document the host's minimum required kernel version, while at it.

Signed-off-by Borislav Petkov <[email protected]>

---
 include/hw/i386/pc.h | 17 +++++++++++++----
 qemu-doc.texi        | 13 +++++++++++++
 target/i386/cpu.c    | 11 ++++-------
 3 files changed, 30 insertions(+), 11 deletions(-)

include/hw/i386/pc.h +13 -4

index 9d29c4b1df2a..ebc28e816b04 100644
@@ -296,6 +296,19 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 
 #define PC_COMPAT_3_1 \
     HW_COMPAT_3_1 \
+    {\
+        .driver   = "Opteron_G3" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G4" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G5" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },
 
 #define PC_COMPAT_3_0 \
     HW_COMPAT_3_0 \

@@ -527,10 +540,6 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
         .driver   = "qemu32" "-" TYPE_X86_CPU,\
         .property = "popcnt",\
         .value    = "on",\
-    },{\
-        .driver   = "Opteron_G2" "-" TYPE_X86_CPU,\
-        .property = "rdtscp",\
-        .value    = "on",\
     },{\
         .driver   = "Opteron_G3" "-" TYPE_X86_CPU,\
         .property = "rdtscp",\

qemu-doc.texi +13 -0

index f7ad1dfe4b69..16b955cbf985 100644
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::

@@ -2813,6 +2814,18 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.
 @end table
 
+@node System requirements
+@chapter System requirements
+
+@section KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.
+
+The OpteronG[345] CPU models require KVM support for RDTSCP, which was
+added with Linux 4.5 which is supported by the major distros. And even
+if RHEL7 has kernel 3.10, KVM there has the required functionality there
+to make it close to a 4.5 or newer kernel.
 
 @include qemu-tech.texi

target/i386/cpu.c +4 -7

index f81d35e1f914..a7def11b27cd 100644
@@ -2706,7 +2706,6 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_DE | CPUID_FP87,
         .features[FEAT_1_ECX] =
             CPUID_EXT_CX16 | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
         .features[FEAT_8000_0001_ECX] =

@@ -2730,9 +2729,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
         .features[FEAT_1_ECX] =
             CPUID_EXT_POPCNT | CPUID_EXT_CX16 | CPUID_EXT_MONITOR |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL |
+            CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_MISALIGNSSE | CPUID_EXT3_SSE4A |
             CPUID_EXT3_ABM | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM,

@@ -2757,10 +2756,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_POPCNT | CPUID_EXT_SSE42 | CPUID_EXT_SSE41 |
             CPUID_EXT_CX16 | CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

@@ -2788,10 +2786,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_AES | CPUID_EXT_POPCNT | CPUID_EXT_SSE42 |
             CPUID_EXT_SSE41 | CPUID_EXT_CX16 | CPUID_EXT_FMA |
             CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_TBM | CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

Signature · 7 lines

2.19.1

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Eduardo Habkost

2018-12-12 19:52 UTC #13 lore raw

Re: [PATCH] target-i386: Reenable RDTSCP support on Opteron_G[345] CPU models

Quoted 45 lines · Borislav Petkov

+ qemu-devel.
Quoted 2 lines · Daniel P. Berrangé
Great, then, this is a non-issue - we just need to mention that fact in the commit that sets the min version for the kernel
Ok, here's a first draft ontop of Eduardo's machine-next branch from
http://github.com/ehabkost/qemu
Also, thanks for the help Eduardo! :-)
---
From: Borislav Petkov <[email protected]>
Date: Tue, 11 Dec 2018 17:01:00 +0100
The missing functionality was added ~3 years ago with the Linux commit
46896c73c1a4 ("KVM: svm: add support for RDTSCP")
so reenable RDTSCP support on those CPU models.
Opteron_G2 - being family 15, model 6, doesn't have RDTSCP support (the real hardware doesn't have it. K8 got RDTSCP support with the NPT models, i.e., models >= 0x40).
Document the host's minimum required kernel version, while at it.
Signed-off-by Borislav Petkov <[email protected]>
---
 include/hw/i386/pc.h | 17 +++++++++++++----
 qemu-doc.texi        | 13 +++++++++++++
 target/i386/cpu.c    | 11 ++++-------
 3 files changed, 30 insertions(+), 11 deletions(-)
include/hw/i386/pc.h +3 -0
index 9d29c4b1df2a..ebc28e816b04 100644
@@ -296,6 +296,19 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 
 #define PC_COMPAT_3_1 \
     HW_COMPAT_3_1 \
+    {\
+        .driver   = "Opteron_G3" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\

include/hw/i386/pc.h bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *); · line 311

Quoted 10 lines

include/hw/i386/pc.h +10 -0

+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G4" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G5" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },

This looks correct.

include/hw/i386/pc.h bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *); · line 533

Quoted 11 lines

include/hw/i386/pc.h +0 -4

 #define PC_COMPAT_3_0 \
     HW_COMPAT_3_0 \

@@ -527,10 +540,6 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
         .driver   = "qemu32" "-" TYPE_X86_CPU,\
         .property = "popcnt",\
         .value    = "on",\
-    },{\
-        .driver   = "Opteron_G2" "-" TYPE_X86_CPU,\
-        .property = "rdtscp",\
-        .value    = "on",\

Why did you remove this entry from PC_COMPAT_2_4?

We must keep compatibility with old behavior of Opteron_G2 on pc-2.4, even if the old behavior was incorrect.

Quoted 39 lines

include/hw/i386/pc.h +0 -0

     },{\
         .driver   = "Opteron_G3" "-" TYPE_X86_CPU,\
         .property = "rdtscp",\

qemu-doc.texi +13 -0

index f7ad1dfe4b69..16b955cbf985 100644
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::

@@ -2813,6 +2814,18 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.
 @end table
 
+@node System requirements
+@chapter System requirements
+
+@section KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.
+
+The OpteronG[345] CPU models require KVM support for RDTSCP, which was
+added with Linux 4.5 which is supported by the major distros. And even
+if RHEL7 has kernel 3.10, KVM there has the required functionality there
+to make it close to a 4.5 or newer kernel.
 
 @include qemu-tech.texi

target/i386/cpu.c +0 -0

index f81d35e1f914..a7def11b27cd 100644

target/i386/cpu.c static X86CPUDefinition builtin_x86_defs[] = { · line 2709

Quoted 4 lines

target/i386/cpu.c +0 -1

@@ -2706,7 +2706,6 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_DE | CPUID_FP87,
         .features[FEAT_1_ECX] =
             CPUID_EXT_CX16 | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */

This is Opteron_G2, and feature is not being added. Looks correct.

target/i386/cpu.c static X86CPUDefinition builtin_x86_defs[] = { · line 2734

Quoted 12 lines

target/i386/cpu.c +2 -2

         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
         .features[FEAT_8000_0001_ECX] =

@@ -2730,9 +2729,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
         .features[FEAT_1_ECX] =
             CPUID_EXT_POPCNT | CPUID_EXT_CX16 | CPUID_EXT_MONITOR |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL |
+            CPUID_EXT2_RDTSCP,

This is Opteron_G3. Looks correct.

target/i386/cpu.c static X86CPUDefinition builtin_x86_defs[] = { · line 2761

Quoted 12 lines

target/i386/cpu.c +1 -2

         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_MISALIGNSSE | CPUID_EXT3_SSE4A |
             CPUID_EXT3_ABM | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM,

@@ -2757,10 +2756,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_POPCNT | CPUID_EXT_SSE42 | CPUID_EXT_SSE41 |
             CPUID_EXT_CX16 | CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,

This is Opteron_G4. Looks correct.

target/i386/cpu.c static X86CPUDefinition builtin_x86_defs[] = { · line 2791

Quoted 12 lines

target/i386/cpu.c +1 -2

         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

@@ -2788,10 +2786,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_AES | CPUID_EXT_POPCNT | CPUID_EXT_SSE42 |
             CPUID_EXT_SSE41 | CPUID_EXT_CX16 | CPUID_EXT_FMA |
             CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,

This is Opteron_G5. Looks correct.

Quoted 11 lines

target/i386/cpu.c +0 -0

         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_TBM | CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

Signature · 7 lines

2.19.1

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Signature · 1 line

Eduardo

Borislav Petkov

author

2018-12-12 20:08 UTC #14 lore raw

PATCH 1/1 target-i386: Reenable RDTSCP support on Opteron_G[345] CPU models CPU models

Quoted 4 lines · Eduardo Habkost

Why did you remove this entry from PC_COMPAT_2_4?
We must keep compatibility with old behavior of Opteron_G2 on pc-2.4, even if the old behavior was incorrect.

Ok, hunk reverted. v2 below.

Thx.

---
From: Borislav Petkov <[email protected]>

The missing functionality was added ~3 years ago with the Linux commit

46896c73c1a4 ("KVM: svm: add support for RDTSCP")

so reenable RDTSCP support on those CPU models.

Opteron_G2 - being family 15, model 6, doesn't have RDTSCP support (the real hardware doesn't have it. K8 got RDTSCP support with the NPT models, i.e., models >= 0x40).

Document the host's minimum required kernel version, while at it.

Signed-off-by Borislav Petkov <[email protected]>

---
v2: Keep Opteron_G2 in PC_COMPAT_2_4 unchanged.

 include/hw/i386/pc.h | 13 +++++++++++++
 qemu-doc.texi        | 13 +++++++++++++
 target/i386/cpu.c    | 11 ++++-------
 3 files changed, 30 insertions(+), 7 deletions(-)

include/hw/i386/pc.h +13 -0

index 9d29c4b1df2a..236d962d2547 100644
@@ -296,6 +296,19 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 
 #define PC_COMPAT_3_1 \
     HW_COMPAT_3_1 \
+    {\
+        .driver   = "Opteron_G3" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G4" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G5" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },
 
 #define PC_COMPAT_3_0 \
     HW_COMPAT_3_0 \

qemu-doc.texi +13 -0

index f7ad1dfe4b69..16b955cbf985 100644
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::

@@ -2813,6 +2814,18 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.
 @end table
 
+@node System requirements
+@chapter System requirements
+
+@section KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.
+
+The OpteronG[345] CPU models require KVM support for RDTSCP, which was
+added with Linux 4.5 which is supported by the major distros. And even
+if RHEL7 has kernel 3.10, KVM there has the required functionality there
+to make it close to a 4.5 or newer kernel.
 
 @include qemu-tech.texi

target/i386/cpu.c +4 -7

index f81d35e1f914..a7def11b27cd 100644
@@ -2706,7 +2706,6 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_DE | CPUID_FP87,
         .features[FEAT_1_ECX] =
             CPUID_EXT_CX16 | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
         .features[FEAT_8000_0001_ECX] =

@@ -2730,9 +2729,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
         .features[FEAT_1_ECX] =
             CPUID_EXT_POPCNT | CPUID_EXT_CX16 | CPUID_EXT_MONITOR |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL |
+            CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_MISALIGNSSE | CPUID_EXT3_SSE4A |
             CPUID_EXT3_ABM | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM,

@@ -2757,10 +2756,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_POPCNT | CPUID_EXT_SSE42 | CPUID_EXT_SSE41 |
             CPUID_EXT_CX16 | CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

@@ -2788,10 +2786,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_AES | CPUID_EXT_POPCNT | CPUID_EXT_SSE42 |
             CPUID_EXT_SSE41 | CPUID_EXT_CX16 | CPUID_EXT_FMA |
             CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_TBM | CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

Signature · 7 lines

2.19.1

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Eduardo Habkost

Applied

2018-12-20 12:10 UTC #15 lore raw

Re: [PATCH -v2] target-i386: Reenable RDTSCP support on Opteron_G[345] CPU models CPU models

Quoted 19 lines · Borislav Petkov

Quoted 4 lines · Eduardo Habkost
Why did you remove this entry from PC_COMPAT_2_4?
We must keep compatibility with old behavior of Opteron_G2 on pc-2.4, even if the old behavior was incorrect.
Ok, hunk reverted. v2 below.
Thx.
---
From: Borislav Petkov <[email protected]>
The missing functionality was added ~3 years ago with the Linux commit
46896c73c1a4 ("KVM: svm: add support for RDTSCP")
so reenable RDTSCP support on those CPU models.

Quoted 7 lines

Opteron_G2 - being family 15, model 6, doesn't have RDTSCP support (the real hardware doesn't have it. K8 got RDTSCP support with the NPT models, i.e., models >= 0x40).
Document the host's minimum required kernel version, while at it.
Signed-off-by Borislav Petkov <[email protected]>

Queued, thanks.

Signature · 1 line

Eduardo

Eduardo Habkost

2018-12-10 19:47 UTC #16 lore raw

In reply to Borislav Petkov

Quoted 6 lines · Borislav Petkov

Quoted 2 lines · Eduardo Habkost
It isn't as simply as reverting commit 33b5e8c03ae7, but we can surely re-add RDTSCP on pc-*-4.0 and newer.
Sure. If you could only point me to an example how to add that to pc-*-4.0 and newer, I'll gladly cook up a patch and test it.

Sorry, I forgot to reply to this part.

See commit 33b5e8c03ae7 for reference. The differences will be:
* Instead of removing RDTSCP from builtin_x86_defs, you'll be adding it.
* Instead of adding rdtscp=on entries to PC_COMPAT_2_4, you'll be adding rdtscp=off entries to PC_COMPAT_3_1.

PC_COMPAT_3_1 is added by the patch that creates the 4.0 machine-types. You can find it on my machine-next branch at:

http://github.com/ehabkost/qemu

Signature · 1 line

Eduardo

Borislav Petkov

author

2018-12-10 20:16 UTC #17 lore raw

Quoted 15 lines · Eduardo Habkost

Quoted 6 lines · Borislav Petkov
Quoted 2 lines · Eduardo Habkost
It isn't as simply as reverting commit 33b5e8c03ae7, but we can surely re-add RDTSCP on pc-*-4.0 and newer.
Sure. If you could only point me to an example how to add that to pc-*-4.0 and newer, I'll gladly cook up a patch and test it.
Sorry, I forgot to reply to this part.
See commit 33b5e8c03ae7 for reference. The differences will be:
* Instead of removing RDTSCP from builtin_x86_defs, you'll be adding it.
* Instead of adding rdtscp=on entries to PC_COMPAT_2_4, you'll be adding rdtscp=off entries to PC_COMPAT_3_1.

Quoted 4 lines

PC_COMPAT_3_1 is added by the patch that creates the 4.0 machine-types. You can find it on my machine-next branch at:
http://github.com/ehabkost/qemu

Thanks for the patient explanation, diff below ontop of your branch.

It is notable to point out that Opteron_G2 - it being family 0xf, model 6 - should not deal with RDTSCP as it doesn't have it.

Although looking at the docs, they say it does but I *have* a K8 laptop which I just checked and it *doesn't* have RDTSCP in CPUID. So lemme clarify that aspect first with folks. :)

---

include/hw/i386/pc.h +13 -4

index 9d29c4b1df2a..ebc28e816b04 100644
@@ -296,6 +296,19 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 
 #define PC_COMPAT_3_1 \
     HW_COMPAT_3_1 \
+    {\
+        .driver   = "Opteron_G3" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G4" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G5" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },
 
 #define PC_COMPAT_3_0 \
     HW_COMPAT_3_0 \

@@ -527,10 +540,6 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
         .driver   = "qemu32" "-" TYPE_X86_CPU,\
         .property = "popcnt",\
         .value    = "on",\
-    },{\
-        .driver   = "Opteron_G2" "-" TYPE_X86_CPU,\
-        .property = "rdtscp",\
-        .value    = "on",\
     },{\
         .driver   = "Opteron_G3" "-" TYPE_X86_CPU,\
         .property = "rdtscp",\

qemu-doc.texi +8 -0

index f7ad1dfe4b69..913b2ef68d54 100644
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::

@@ -2813,6 +2814,13 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.
 @end table
 
+@node System requirements
+@chapter System requirements
+
+@section KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.
 
 @include qemu-tech.texi

target/i386/cpu.c +4 -7

index f81d35e1f914..a7def11b27cd 100644
@@ -2706,7 +2706,6 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_DE | CPUID_FP87,
         .features[FEAT_1_ECX] =
             CPUID_EXT_CX16 | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
         .features[FEAT_8000_0001_ECX] =

@@ -2730,9 +2729,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
         .features[FEAT_1_ECX] =
             CPUID_EXT_POPCNT | CPUID_EXT_CX16 | CPUID_EXT_MONITOR |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL |
+            CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_MISALIGNSSE | CPUID_EXT3_SSE4A |
             CPUID_EXT3_ABM | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM,

@@ -2757,10 +2756,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_POPCNT | CPUID_EXT_SSE42 | CPUID_EXT_SSE41 |
             CPUID_EXT_CX16 | CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

@@ -2788,10 +2786,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_AES | CPUID_EXT_POPCNT | CPUID_EXT_SSE42 |
             CPUID_EXT_SSE41 | CPUID_EXT_CX16 | CPUID_EXT_FMA |
             CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_TBM | CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

Signature · 4 lines

Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.