lkml.org 
[lkml]   [2019]   [Jan]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH AUTOSEL 4.14 085/170] iommu/arm-smmu-v3: Use explicit mb() when moving cons pointer
    Date
    From: Will Deacon <will.deacon@arm.com>

    [ 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 26e99c03390f..09eb258a9a7d 100644
    --- a/drivers/iommu/arm-smmu-v3.c
    +++ b/drivers/iommu/arm-smmu-v3.c
    @@ -730,7 +730,13 @@ 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)
    --
    2.19.1
    \
     
     \ /
      Last update: 2019-01-28 18:01    [W:5.243 / U:0.260 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site