iommu/arm-smmu-v3: Fix unexpected CMD_SYNC timeout

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The condition break condition of:

	(int)(VAL - sync_idx) >= 0

in the __arm_smmu_sync_poll_msi() polling loop requires that sync_idx
must be increased monotonically according to the sequence of the CMDs in
the cmdq.

However, since the msidata is populated using atomic_inc_return_relaxed()
before taking the command-queue spinlock, then the following scenario
can occur:

CPU0			CPU1
msidata=0
			msidata=1
			insert cmd1
insert cmd0
			smmu execute cmd1
smmu execute cmd0
			poll timeout, because msidata=1 is overridden by
			cmd0, that means VAL=0, sync_idx=1.

This is not a functional problem, since the caller will eventually either
timeout or exit due to another CMD_SYNC, however it's clearly not what
the code is supposed to be doing. Fix it, by incrementing the sequence
count with the command-queue lock held, allowing us to drop the atomic
operations altogether.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[will: dropped the specialised cmd building routine for now]
Signed-off-by: Will Deacon <will.deacon@arm.com>

...

This commit is contained in:

Zhen Lei 2018-08-19 15:51:10 +08:00 • committed by Will Deacon

parent 85c7a0f1ef

commit 0f02477d16

1 changed files with 3 additions and 5 deletions

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drivers/iommu/arm-smmu-v3.c

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