[lkml]   [2019]   [Feb]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 4.9 046/137] iommu/arm-smmu-v3: Use explicit mb() when moving cons pointer
4.9-stable review patch.  If anyone has any objections, please let me know.


[ 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 <>
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 ff4be1174ff0..7bd98585d78d 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -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)

 \ /
  Last update: 2019-02-11 16:16    [W:0.328 / U:2.412 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site