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iommu/arm-smmu-v3: Use explicit mb() when moving cons pointer

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[ Upstream commit a868e85304 ]

After removing an entry from a queue (e.g. reading an event in
arm_smmu_evtq_thread()) it is necessary to advance the MMIO consumer
pointer to free the queue slot back to the SMMU. A memory barrier is
required here so that all reads targetting the queue entry have
completed before the consumer pointer is updated.

The implementation of queue_inc_cons() relies on a writel() to complete
the previous reads, but this is incorrect because writel() is only
guaranteed to complete prior writes. This patch replaces the call to
writel() with an mb(); writel_relaxed() sequence, which gives us the
read->write ordering which we require.

Cc: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Will Deacon 2018-11-07 22:58:24 +00:00 committed by Greg Kroah-Hartman
parent 98e089c8b7
commit d1069fc142
1 changed files with 7 additions and 1 deletions
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8
drivers/iommu/arm-smmu-v3.c
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@ -697,7 +697,13 @@ static void queue_inc_cons(struct arm_smmu_queue *q)
u32 cons = (Q_WRP(q, q->cons) | Q_IDX(q, q->cons)) + 1;
q->cons = Q_OVF(q, q->cons) | Q_WRP(q, cons) | Q_IDX(q, cons);
writel(q->cons, q->cons_reg);
/*
* Ensure that all CPU accesses (reads and writes) to the queue
* are complete before we update the cons pointer.
*/
mb();
writel_relaxed(q->cons, q->cons_reg);
}
static int queue_sync_prod(struct arm_smmu_queue *q)