[PATCH] iommu/amd: Remove iommu_group_mutex_assert() from amd_iommu_clear_gcr3()

[PATCH] iommu/amd: Remove iommu_group_mutex_assert() from amd_iommu_clear_gcr3()

[Vasant Hegde]

amd_iommu_clear_gcr3() is called from sva_mn_release() during the
mmu_notifier release path to detach a PASIDs when a process exits.
This path does not hold the iommu group mutex, since it is invoked
asynchronously from mm teardown context rather than through the normal
IOMMU group/attach APIs.

As a result, the iommu_group_mutex_assert() check in
amd_iommu_clear_gcr3() logs a kernel warning.

[62863.761300] ------------[ cut here ]------------
[62863.761320] WARNING: drivers/iommu/iommu.c:1361 at iommu_group_mutex_assert+0x3a/0x50, CPU#14: kworker/14:2/621
...
[62863.761706]  <TASK>
[62863.761712]  amd_iommu_clear_gcr3+0x1e/0x50
[62863.761724]  sva_mn_release+0x68/0xd0
[62863.761739]  __mmu_notifier_release+0xb9/0x2d0
[62863.761763]  exit_mmap+0x427/0x460
[62863.761836]  __mmput+0x41/0x120
[62863.761844]  mmput_async_fn+0x15/0x20
[62863.761852]  process_one_work+0x22e/0x780
[62863.761876]  worker_thread+0x1b5/0x380
[62863.761892]  kthread+0x10d/0x150
[62863.761913]  ret_from_fork+0x346/0x3c0
[62863.761930]  ret_from_fork_asm+0x1a/0x30
[62863.761964]  </TASK>

Remove the iommu_group_mutex_assert() call from
amd_iommu_clear_gcr3(), since PASID teardown via the mmu_notifier
release path is a legitimate caller that does not and need not hold
the group mutex.

Fixes: 1af95763e0a3 ("iommu/amd: Initial SVA support for AMD IOMMU")
Reported-by: Max Zhen <max.zhen@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Tested-by: Liang Wendy <Wendy.Liang@amd.com>
---
 drivers/iommu/amd/iommu.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 29dc18d3d22e..1fe99fb98793 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -2063,8 +2063,6 @@ int amd_iommu_clear_gcr3(struct iommu_dev_data *dev_data, ioasid_t pasid)
 	struct gcr3_tbl_info *gcr3_info = &dev_data->gcr3_info;
 	int ret;
 
-	iommu_group_mutex_assert(dev_data->dev);
-
 	ret = update_gcr3(dev_data, pasid, 0, false);
 	if (ret)
 		return ret;
-- 
2.31.1

Re: [PATCH] iommu/amd: Remove iommu_group_mutex_assert() from amd_iommu_clear_gcr3()

[Jason Gunthorpe]

On Fri, Aug 14, 2026 at 10:40:29AM +0000, Vasant Hegde wrote:

> Remove the iommu_group_mutex_assert() call from
> amd_iommu_clear_gcr3(), since PASID teardown via the mmu_notifier
> release path is a legitimate caller that does not and need not hold
> the group mutex.

Why doesn't it?

Right below this line is:

	gcr3_info->pasid_cnt--;

Which certainly needs the lock.

In the ARM driver this async release notifier was pretty tricky to
lock properly. It just updates the equivilent to the GCR3 entry to
make it disabled and doesn't touch anything else. This is locked in a
way so that concurrent domain detach doesn't face any races.

AMD should have the same basic design here too.

Jason

Re: [PATCH] iommu/amd: Remove iommu_group_mutex_assert() from amd_iommu_clear_gcr3()

[Jörg Rödel]

On Fri, Aug 14, 2026 at 10:40:29AM +0000, Vasant Hegde wrote:
> Remove the iommu_group_mutex_assert() call from
> amd_iommu_clear_gcr3(), since PASID teardown via the mmu_notifier
> release path is a legitimate caller that does not and need not hold
> the group mutex.

Jason is right, there is a race around pasid_cnt. Either make that atomic, or,
since it is never read, remove it.

-Joerg