4.4-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit a868e8530441286342f90c1fd9c5f24de3aa2880 ]
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 --- drivers/iommu/arm-smmu-v3.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c index fc6eb752ab35..eb9937225d64 100644 --- a/drivers/iommu/arm-smmu-v3.c +++ b/drivers/iommu/arm-smmu-v3.c @@ -683,7 +683,13 @@ 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)