From: Will Deacon Date: Wed, 7 Nov 2018 22:58:24 +0000 (+0000) Subject: iommu/arm-smmu-v3: Use explicit mb() when moving cons pointer X-Git-Tag: v4.19.21~190 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=710e1e561630975f934214c0196133fa12a86514;p=platform%2Fkernel%2Flinux-rpi.git iommu/arm-smmu-v3: Use explicit mb() when moving cons pointer [ 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 Signed-off-by: Will Deacon Signed-off-by: Sasha Levin --- diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c index 4afb9cb..9ae3678 100644 --- a/drivers/iommu/arm-smmu-v3.c +++ b/drivers/iommu/arm-smmu-v3.c @@ -688,7 +688,13 @@ 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)