iommu: Fix the longstanding probe issues

 drivers/iommu/iommu.c | 5 +++++
 1 file changed, 5 insertions(+)

drivers/iommu/iommu.c +0 -0

index 870c3cdbd0f6..2486f6d6ef68 100644

Thanks a lot for posting these patches, Robin.

Quoted 8 lines · Robin Murphy

  drivers/iommu/iommu.c | 5 +++++
  1 file changed, 5 insertions(+)

drivers/iommu/iommu.c +0 -0

index 870c3cdbd0f6..2486f6d6ef68 100644

drivers/iommu/iommu.c int iommu_device_use_default_domain(struct device *dev) · line 3104

Quoted 8 lines

drivers/iommu/iommu.c +5 -0

@@ -3097,6 +3097,11 @@ int iommu_device_use_default_domain(struct device *dev)
  		return 0;
 
  	mutex_lock(&group->mutex);
+	/* We may race against bus_iommu_probe() finalising groups here */
+	if (!group->default_domain) {
+		ret = -EPROBE_DEFER;
+		goto unlock_out;
+	}

We just hit the issue again even after picking up this patch, though very hard to reproduce, on 6.6 LTS.

After code inspection, it seems the issue is that - default domain is setup in the bus_iommu_probe() before hitting of this replay.

A:async client probe in platform_dma_configure(), B:bus_iommu_probe() :-

1) A: sets up iommu_fwspec under iommu_probe_device_lock.

2) B: Sets the dev->iommu_group under iommu_probe_device_lock. Domain setup is deferred.

3) A: Returns with out allocating the default domain, as dev->iommu_group is set, whose checks are also made under the same 'iommu_probe_device_lock'. __This miss setting of the valid dev->dma_ops__.

4) B: Sets up the group->default_domain under group->mutex.

5) A: iommu_device_use_default_domain(): Relies on this group->default_domain, under the same mutex, to decide if need to go for replay, which is skipped. This is skipping the setting up of valid dma_ops and that's an issue.

But I don't think that the same issue exists on 6.13 because of your patch, b67483b3c44e ("iommu/dma: Centralise iommu_setup_dma_ops()"). bus_iommu_probe():

      list_for_each_entry_safe(group, next, &group_list, entry) {
		mutex_lock(&group->mutex);
		for_each_group_device(group, gdev)
			iommu_setup_dma_ops(gdev->dev);
		mutex_unlock(&group->mutex);
      }

This makes the step4 above force to use the valid dma_iommu api, thus I see no issue when there is no probe deferral.

So, I think we are good with this patch on 6.13.

Now coming back to 6.6 LTS, any ideas you have here, please?

drivers/iommu/iommu.c int iommu_device_use_default_domain(struct device *dev) · line 3107

Quoted 4 lines

drivers/iommu/iommu.c +0 -0

  	if (group->owner_cnt) {
  		if (group->domain != group->default_domain || group->owner ||
  		    !xa_empty(&group->pasid_array)) {

Thanks,
Charan

It turns out that deferred default domain creation leaves a subtle race window during iommu_device_register() wherein a client driver may asynchronously probe in parallel and get as far as performing DMA API operations with dma-direct, only to be switched to iommu-dma underfoot once the default domain attachment finally happens, with obviously disastrous consequences. Even the wonky of_iommu_configure() path is at risk, since iommu_fwspec_init() will no longer defer client probe as the instance ops are (necessarily) already registered, and the "replay" iommu_probe_device() call can see dev->iommu_group already set and so think there's nothing to do either.

Fortunately we already have the right tool in the right place in the form of iommu_device_use_default_domain(), which just needs to ensure that said default domain is actually ready to *be* used. Deferring the client probe shouldn't have too much impact, given that this only happens while the IOMMU driver is probing, and thus due to kick the deferred probe list again once it finishes.

Reported-by Charan Teja Kalla <[email protected]>

Fixes 98ac73f99bc4 ("iommu: Require a default_domain for all iommu drivers")

Signed-off-by Robin Murphy <[email protected]>

---
 drivers/iommu/iommu.c | 5 +++++
 1 file changed, 5 insertions(+)

In hindsight, there were some crucial subtleties overlooked when moving {of,acpi}_dma_configure() to driver probe time to allow waiting for IOMMU drivers with -EPROBE_DEFER, and these have become an ever-increasing source of problems. The IOMMU API has some fundamental assumptions that iommu_probe_device() is called for every device added to the system, in the order in which they are added. Calling it in a random order or not at all dependent on driver binding leads to malformed groups, a potential lack of isolation for devices with no driver, and all manner of unexpected concurrency and race conditions. We've attempted to mitigate the latter with point-fix bodges like iommu_probe_device_lock, but it's a losing battle and the time has come to bite the bullet and address the true source of the problem instead.

The crux of the matter is that the firmware parsing actually serves two distinct purposes; one is identifying the IOMMU instance associated with a device so we can check its availability, the second is actually telling that instance about the relevant firmware-provided data for the device. However the latter also depends on the former, and at the time there was no good place to defer and retry that separately from the availability check we also wanted for client driver probe.

Nowadays, though, we have a proper notion of multiple IOMMU instances in the core API itself, and each one gets a chance to probe its own devices upon registration, so we can finally make that work as intended for DT/IORT/VIOT platforms too. All we need is for iommu_probe_device() to be able to run the iommu_fwspec machinery currently buried deep in the wrong end of {of,acpi}_dma_configure(). Luckily it turns out to be surprisingly straightforward to bootstrap this transformation by pretty much just calling the same path twice. At client driver probe time, dev->driver is obviously set; conversely at device_add(), or a subsequent bus_iommu_probe(), any device waiting for an IOMMU really should *not* have a driver already, so we can use that as a condition to disambiguate the two cases, and avoid recursing back into the IOMMU core at the wrong times.

Obviously this isn't the nicest thing, but for now it gives us a functional baseline to then unpick the layers in between without many more awkward cross-subsystem patches. There are some minor side-effects like dma_range_map potentially being created earlier, and some debug prints being repeated, but these aren't significantly detrimental. Let's make things work first, then deal with making them nice.

With the basic flow finally in the right order again, the next step is probably turning the bus->dma_configure paths inside-out, since all we really need from bus code is its notion of which device and input ID(s) to parse the common firmware properties with...

Signed-off-by Robin Murphy <[email protected]>

---
 drivers/acpi/arm64/dma.c        |  5 ++++
 drivers/acpi/scan.c             | 10 +++-----
 drivers/amba/bus.c              |  2 +-
 drivers/base/platform.c         |  2 +-
 drivers/bus/fsl-mc/fsl-mc-bus.c |  2 +-
 drivers/cdx/cdx.c               |  2 +-
 drivers/iommu/iommu.c           | 43 ++++++++++++++++++++++++---------
 drivers/iommu/of_iommu.c        | 10 +++++++-
 drivers/of/device.c             |  7 +++++-
 drivers/pci/pci-driver.c        |  2 +-

 10 files changed, 60 insertions(+), 25 deletions(-)

drivers/acpi/arm64/dma.c +5 -0

index 52b2abf88689..f30f138352b7 100644
@@ -26,6 +26,11 @@ void acpi_arch_dma_setup(struct device *dev)
 	else
 		end = (1ULL << 32) - 1;
 
+	if (dev->dma_range_map) {
+		dev_dbg(dev, "dma_range_map already set\n");
+		return;
+	}
+
 	ret = acpi_dma_get_range(dev, &map);
 	if (!ret && map) {
 		end = dma_range_map_max(map);

drivers/acpi/scan.c +3 -7

index 9f4efa8f75a6..42b8f1833c3c 100644
@@ -1619,6 +1619,9 @@ static int acpi_iommu_configure_id(struct device *dev, const u32 *id_in)
 {
 	int err;
 
+	if (device_iommu_mapped(dev))
+		return 0;
+
 	/* Serialise to make dev->iommu stable under our potential fwspec */
 	mutex_lock(&iommu_probe_device_lock);
 	/* If we already translated the fwspec there is nothing left to do */

@@ -1632,13 +1635,6 @@ static int acpi_iommu_configure_id(struct device *dev, const u32 *id_in)
 		err = viot_iommu_configure(dev);
 	mutex_unlock(&iommu_probe_device_lock);
 
-	/*
-	 * If we have reason to believe the IOMMU driver missed the initial
-	 * iommu_probe_device() call for dev, replay it to get things in order.
-	 */
-	if (!err && dev->bus)
-		err = iommu_probe_device(dev);
-
 	return err;
 }
 

drivers/amba/bus.c +1 -1

index 8ef259b4d037..abbb37d4d228 100644
@@ -364,7 +364,7 @@ static int amba_dma_configure(struct device *dev)
 		ret = acpi_dma_configure(dev, attr);
 	}
 
-	if (!ret && !drv->driver_managed_dma) {
+	if (dev->driver && !ret && !drv->driver_managed_dma) {
 		ret = iommu_device_use_default_domain(dev);
 		if (ret)
 			arch_teardown_dma_ops(dev);

drivers/base/platform.c +1 -1

index 6f2a33722c52..4c7570d637f9 100644
@@ -1451,7 +1451,7 @@ static int platform_dma_configure(struct device *dev)
 		attr = acpi_get_dma_attr(to_acpi_device_node(fwnode));
 		ret = acpi_dma_configure(dev, attr);
 	}
-	if (ret || drv->driver_managed_dma)
+	if (!dev->driver || ret || drv->driver_managed_dma)
 		return ret;
 
 	ret = iommu_device_use_default_domain(dev);

drivers/bus/fsl-mc/fsl-mc-bus.c +1 -1

index d1f3d327ddd1..fb58833b222a 100644
@@ -153,7 +153,7 @@ static int fsl_mc_dma_configure(struct device *dev)
 	else
 		ret = acpi_dma_configure_id(dev, DEV_DMA_COHERENT, &input_id);
 
-	if (!ret && !mc_drv->driver_managed_dma) {
+	if (dev->driver && !ret && !mc_drv->driver_managed_dma) {
 		ret = iommu_device_use_default_domain(dev);
 		if (ret)
 			arch_teardown_dma_ops(dev);

drivers/cdx/cdx.c +1 -1

index c573ed2ee71a..d5761b96a412 100644
@@ -360,7 +360,7 @@ static int cdx_dma_configure(struct device *dev)
 		return ret;
 	}
 
-	if (!ret && !cdx_drv->driver_managed_dma) {
+	if (dev->driver && !ret && !cdx_drv->driver_managed_dma) {
 		ret = iommu_device_use_default_domain(dev);
 		if (ret)
 			arch_teardown_dma_ops(dev);

drivers/iommu/iommu.c +32 -11

index 2486f6d6ef68..89f634d46aad 100644
@@ -519,17 +519,6 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list
 	struct group_device *gdev;
 	int ret;
 
-	/*
-	 * For FDT-based systems and ACPI IORT/VIOT, drivers register IOMMU
-	 * instances with non-NULL fwnodes, and client devices should have been
-	 * identified with a fwspec by this point. Otherwise, we can currently
-	 * assume that only one of Intel, AMD, s390, PAMU or legacy SMMUv2 can
-	 * be present, and that any of their registered instances has suitable
-	 * ops for probing, and thus cheekily co-opt the same mechanism.
-	 */
-	ops = iommu_fwspec_ops(dev_iommu_fwspec_get(dev));
-	if (!ops)
-		return -ENODEV;
 	/*
 	 * Serialise to avoid races between IOMMU drivers registering in
 	 * parallel and/or the "replay" calls from ACPI/OF code via client

@@ -539,9 +528,41 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list
 	 */
 	lockdep_assert_held(&iommu_probe_device_lock);
 
+	/*
+	 * For FDT-based systems and ACPI IORT/VIOT, the common firmware parsing
+	 * is buried in the bus dma_configure path. Properly unpicking that is
+	 * still a fairly big job, so for now just invoke the whole thing. Our
+	 * bus_iommu_probe() walk may see devices with drivers already bound,
+	 * but that must mean they're already configured - either probed by
+	 * another IOMMU, or there was no IOMMU for iommu_fwspec_init() to wait
+	 * for - so either way we can safely skip this and avoid worrying about
+	 * those recursing back here thinking they need a replay call.
+	 */
+	if (!dev->driver && dev->bus->dma_configure) {
+		mutex_unlock(&iommu_probe_device_lock);
+		dev->bus->dma_configure(dev);
+		mutex_lock(&iommu_probe_device_lock);
+	}
+
+	/*
+	 * At this point, either valid devices now have a fwspec, or we can
+	 * assume that only one of Intel, AMD, s390, PAMU or legacy SMMUv2 can
+	 * be present, and that any of their registered instances has suitable
+	 * ops for probing, and thus cheekily co-opt the same mechanism.
+	 */
+	ops = iommu_fwspec_ops(dev_iommu_fwspec_get(dev));
+	if (!ops)
+		return -ENODEV;
+
 	/* Device is probed already if in a group */
 	if (dev->iommu_group)
 		return 0;
+	/*
+	 * And if we do now see any replay calls, they would indicate someone
+	 * misusing the dma_configure path outside bus code.
+	 */
+	if (dev_iommu_fwspec_get(dev) && dev->driver)
+		dev_WARN(dev, "late IOMMU probe at driver bind, something fishy here!\n");
 
 	ret = iommu_init_device(dev, ops);
 	if (ret)

drivers/iommu/of_iommu.c +9 -1

index 97987cd78da9..c9aaf5783b77 100644
@@ -121,6 +121,9 @@ int of_iommu_configure(struct device *dev, struct device_node *master_np,
 	if (!master_np)
 		return -ENODEV;
 
+	if (device_iommu_mapped(dev))
+		return 0;
+
 	/* Serialise to make dev->iommu stable under our potential fwspec */
 	mutex_lock(&iommu_probe_device_lock);
 	if (dev_iommu_fwspec_get(dev)) {

@@ -151,7 +154,12 @@ int of_iommu_configure(struct device *dev, struct device_node *master_np,
 		iommu_fwspec_free(dev);
 	mutex_unlock(&iommu_probe_device_lock);
 
-	if (!err && dev->bus)
+	/*
+	 * If we have reason to believe the IOMMU driver missed the initial
+	 * iommu_probe_device() call for dev, try to fix it up. This should
+	 * no longer happen unless of_dma_configure() is being misused.
+	 */
+	if (!err && dev->driver)
 		err = iommu_probe_device(dev);
 
 	if (err && err != -EPROBE_DEFER)

drivers/of/device.c +6 -1

index edf3be197265..5053e5d532cc 100644
@@ -99,6 +99,11 @@ int of_dma_configure_id(struct device *dev, struct device_node *np,
 	bool coherent, set_map = false;
 	int ret;
 
+	if (dev->dma_range_map) {
+		dev_dbg(dev, "dma_range_map already set\n");
+		goto skip_map;
+	}
+
 	if (np == dev->of_node)
 		bus_np = __of_get_dma_parent(np);
 	else

@@ -119,7 +124,7 @@ int of_dma_configure_id(struct device *dev, struct device_node *np,
 		end = dma_range_map_max(map);
 		set_map = true;
 	}
-
+skip_map:
 	/*
 	 * If @dev is expected to be DMA-capable then the bus code that created
 	 * it should have initialised its dma_mask pointer by this point. For

drivers/pci/pci-driver.c +1 -1

index f57ea36d125d..143b2f2081ea 100644
@@ -1653,7 +1653,7 @@ static int pci_dma_configure(struct device *dev)
 
 	pci_put_host_bridge_device(bridge);
 
-	if (!ret && !driver->driver_managed_dma) {
+	if (dev->driver && !ret && !driver->driver_managed_dma) {
 		ret = iommu_device_use_default_domain(dev);
 		if (ret)
 			arch_teardown_dma_ops(dev);

Signature · 1 line

2.39.2.101.g768bb238c484.dirty

much just calling the same path twice. At client driver probe time, dev->driver is obviously set; conversely at device_add(), or a subsequent bus_iommu_probe(), any device waiting for an IOMMU really

should *not* have a driver already, so we can use that as a condition to disambiguate the two cases, and avoid recursing back into the IOMMU core at the wrong times.

drivers/acpi/scan.c +19 -0

+	/*
+	 * For FDT-based systems and ACPI IORT/VIOT, the common firmware parsing
+	 * is buried in the bus dma_configure path. Properly unpicking that is
+	 * still a fairly big job, so for now just invoke the whole thing. Our
+	 * bus_iommu_probe() walk may see devices with drivers already bound,
+	 * but that must mean they're already configured - either probed by
+	 * another IOMMU, or there was no IOMMU for iommu_fwspec_init() to wait
+	 * for - so either way we can safely skip this and avoid worrying about
+	 * those recursing back here thinking they need a replay call.
+	 */
+	if (!dev->driver && dev->bus->dma_configure) {
+		mutex_unlock(&iommu_probe_device_lock);
+		dev->bus->dma_configure(dev);
+		mutex_lock(&iommu_probe_device_lock);
+	}
+
+	/*
+	 * At this point, either valid devices now have a fwspec, or we can
+	 * assume that only one of Intel, AMD, s390, PAMU or legacy SMMUv2 can

Quoted 3 lines · Robin Murphy

much just calling the same path twice. At client driver probe time, dev->driver is obviously set; conversely at device_add(), or a subsequent bus_iommu_probe(), any device waiting for an IOMMU really

Could you put the dev->driver test into iommu_device_use_default_domain()?

It looks like many of the cases are just guarding that call.

Quoted 3 lines

should *not* have a driver already, so we can use that as a condition to disambiguate the two cases, and avoid recursing back into the IOMMU core at the wrong times.

Which sounds like this:

drivers/iommu/iommu.c static int __iommu_probe_device(struct device *dev, struct list_head *group_list · line 545

Quoted 4 lines

drivers/iommu/iommu.c +4 -0

+		mutex_unlock(&iommu_probe_device_lock);
+		dev->bus->dma_configure(dev);
+		mutex_lock(&iommu_probe_device_lock);
+	}

Shouldn't call iommu_device_use_default_domain() ?

But... I couldn't guess what the problem with calling it is?

In the not-probed case it will see dev->iommu_group is NULL and succeed.

The probed case could be prevented by checking dev->iommu_group sooner in __iommu_probe_device()?

Anyhow, the approach seems OK

Quoted 8 lines

drivers/acpi/scan.c +0 -0

index 9f4efa8f75a6..42b8f1833c3c 100644
@@ -1619,6 +1619,9 @@ static int acpi_iommu_configure_id(struct device *dev, const u32 *id_in)
  {
  	int err;
 

drivers/acpi/scan.c static int acpi_iommu_configure_id(struct device *dev, const u32 *id_in) · line 1623

Quoted 2 lines

drivers/acpi/scan.c +2 -0

+	if (device_iommu_mapped(dev))
+		return 0;

This is unlocked and outside a driver context, it should have a comment explaining why races with probe can't happen?

Quoted 25 lines

drivers/acpi/scan.c +25 -0

+	/*
+	 * For FDT-based systems and ACPI IORT/VIOT, the common firmware parsing
+	 * is buried in the bus dma_configure path. Properly unpicking that is
+	 * still a fairly big job, so for now just invoke the whole thing. Our
+	 * bus_iommu_probe() walk may see devices with drivers already bound,
+	 * but that must mean they're already configured - either probed by
+	 * another IOMMU, or there was no IOMMU for iommu_fwspec_init() to wait
+	 * for - so either way we can safely skip this and avoid worrying about
+	 * those recursing back here thinking they need a replay call.
+	 */
+	if (!dev->driver && dev->bus->dma_configure) {
+		mutex_unlock(&iommu_probe_device_lock);
+		dev->bus->dma_configure(dev);
+		mutex_lock(&iommu_probe_device_lock);
+	}
+
+	/*
+	 * At this point, either valid devices now have a fwspec, or we can
+	 * assume that only one of Intel, AMD, s390, PAMU or legacy SMMUv2 can
+	 * be present, and that any of their registered instances has suitable
+	 * ops for probing, and thus cheekily co-opt the same mechanism.
+	 */
+	ops = iommu_fwspec_ops(dev_iommu_fwspec_get(dev));
+	if (!ops)
+		return -ENODEV;

Quoted 4 lines

+
/* Device is probed already if in a group */ if (dev->iommu_group)
return 0;

This is the test I mean, if iommu_group is set then dev->iommu->iommu_dev->ops is supposed to be valid too. It seems like it should be done earlier..

drivers/acpi/scan.c

Quoted 6 lines

drivers/acpi/scan.c +6 -0

+	/*
+	 * And if we do now see any replay calls, they would indicate someone
+	 * misusing the dma_configure path outside bus code.
+	 */
+	if (dev_iommu_fwspec_get(dev) && dev->driver)
+		dev_WARN(dev, "late IOMMU probe at driver bind, something fishy here!\n");

WARN_ON_ONCE or dump_stack() to get the stack trace out?

drivers/acpi/scan.c int of_iommu_configure(struct device *dev, struct device_node *master_np, · line 125

Quoted 6 lines

drivers/acpi/scan.c +2 -0

@@ -121,6 +121,9 @@ int of_iommu_configure(struct device *dev, struct device_node *master_np,
  	if (!master_np)
  		return -ENODEV;
 
+	if (device_iommu_mapped(dev))
+		return 0;

Same note

Quoted 4 lines

drivers/acpi/scan.c +0 -0

@@ -151,7 +154,12 @@ int of_iommu_configure(struct device *dev, struct device_node *master_np,
  		iommu_fwspec_free(dev);
  	mutex_unlock(&iommu_probe_device_lock);
 

drivers/acpi/scan.c int of_iommu_configure(struct device *dev, struct device_node *master_np, · line 163

Quoted 8 lines

drivers/acpi/scan.c +6 -1

-	if (!err && dev->bus)
+	/*
+	 * If we have reason to believe the IOMMU driver missed the initial
+	 * iommu_probe_device() call for dev, try to fix it up. This should
+	 * no longer happen unless of_dma_configure() is being misused.
+	 */
+	if (!err && dev->driver)
  		err = iommu_probe_device(dev);

This is being conservative? After some time of nobody complaining it can be removed?

Quoted 14 lines · Jason Gunthorpe

Quoted 3 lines · Robin Murphy

much just calling the same path twice. At client driver probe time, dev->driver is obviously set; conversely at device_add(), or a subsequent bus_iommu_probe(), any device waiting for an IOMMU really

Could you put the dev->driver test into iommu_device_use_default_domain()?

It looks like many of the cases are just guarding that call.

Quoted 3 lines

should *not* have a driver already, so we can use that as a condition to disambiguate the two cases, and avoid recursing back into the IOMMU core at the wrong times.

Quoted 8 lines

Which sounds like this:

drivers/iommu/iommu.c static int __iommu_probe_device(struct device *dev, struct list_head *group_list · line 545

Quoted 4 lines

drivers/iommu/iommu.c +4 -0

+		mutex_unlock(&iommu_probe_device_lock);
+		dev->bus->dma_configure(dev);
+		mutex_lock(&iommu_probe_device_lock);
+	}

Shouldn't call iommu_device_use_default_domain() ?

Semantically it shouldn't really be called at this stage, but it won't be anyway since "to_<x>_driver(NULL)->driver_managed_dma" is not false - trouble is it's also not true ;)

Quoted 3 lines

This is the test I mean, if iommu_group is set then dev->iommu->iommu_dev->ops is supposed to be valid too. It seems like it should be done earlier..

Yeah, looking at it now I'm really not sure why this ended up in this order
- I guess I was effectively adding the dma_configure() call to the front of the existing iommu_fwspec_ops() check, and then I moved the lockdep_assert() up to make more sense. But then the ops check probably should have been after the group check to begin with, for much the same reasoning as above. I'll sort that out for v2.

Quoted 7 lines

drivers/iommu/iommu.c static int __iommu_probe_device(struct device *dev, struct list_head *group_list · line 565

Quoted 5 lines

drivers/iommu/iommu.c +5 -0

+	 * And if we do now see any replay calls, they would indicate someone
+	 * misusing the dma_configure path outside bus code.
+	 */
+	if (dev_iommu_fwspec_get(dev) && dev->driver)
+		dev_WARN(dev, "late IOMMU probe at driver bind, something fishy here!\n");

WARN_ON_ONCE or dump_stack() to get the stack trace out?

Indeed, hence dev_WARN() (!= dev_warn())

In hindsight, there were some crucial subtleties overlooked when moving {of,acpi}_dma_configure() to driver probe time to allow waiting for IOMMU drivers with -EPROBE_DEFER, and these have become an ever-increasing source of problems. The IOMMU API has some fundamental assumptions that iommu_probe_device() is called for every device added to the system, in the order in which they are added. Calling it in a random order or not at all dependent on driver binding leads to malformed groups, a potential lack of isolation for devices with no driver, and all manner of unexpected concurrency and race conditions. We've attempted to mitigate the latter with point-fix bodges like iommu_probe_device_lock, but it's a losing battle and the time has come to bite the bullet and address the true source of the problem instead.

The crux of the matter is that the firmware parsing actually serves two distinct purposes; one is identifying the IOMMU instance associated with a device so we can check its availability, the second is actually telling that instance about the relevant firmware-provided data for the device. However the latter also depends on the former, and at the time there was no good place to defer and retry that separately from the availability check we also wanted for client driver probe.

Nowadays, though, we have a proper notion of multiple IOMMU instances in the core API itself, and each one gets a chance to probe its own devices upon registration, so we can finally make that work as intended for DT/IORT/VIOT platforms too. All we need is for iommu_probe_device() to be able to run the iommu_fwspec machinery currently buried deep in the wrong end of {of,acpi}_dma_configure(). Luckily it turns out to be surprisingly straightforward to bootstrap this transformation by pretty much just calling the same path twice. At client driver probe time, dev->driver is obviously set; conversely at device_add(), or a subsequent bus_iommu_probe(), any device waiting for an IOMMU really should *not* have a driver already, so we can use that as a condition to disambiguate the two cases, and avoid recursing back into the IOMMU core at the wrong times.

Obviously this isn't the nicest thing, but for now it gives us a functional baseline to then unpick the layers in between without many more awkward cross-subsystem patches. There are some minor side-effects like dma_range_map potentially being created earlier, and some debug prints being repeated, but these aren't significantly detrimental. Let's make things work first, then deal with making them nice.

With the basic flow finally in the right order again, the next step is probably turning the bus->dma_configure paths inside-out, since all we really need from bus code is its notion of which device and input ID(s) to parse the common firmware properties with...

Signed-off-by Robin Murphy <[email protected]>

---
 drivers/acpi/arm64/dma.c        |  5 ++++
 drivers/acpi/scan.c             | 10 +++-----
 drivers/amba/bus.c              |  2 +-
 drivers/base/platform.c         |  2 +-
 drivers/bus/fsl-mc/fsl-mc-bus.c |  2 +-
 drivers/cdx/cdx.c               |  2 +-
 drivers/iommu/iommu.c           | 43 ++++++++++++++++++++++++---------
 drivers/iommu/of_iommu.c        | 10 +++++++-
 drivers/of/device.c             |  7 +++++-

 drivers/pci/pci-driver.c        |  2 +-
 10 files changed, 60 insertions(+), 25 deletions(-)