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nvme-pci: dma read memory barrier for completions

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Control dependencies do not guarantee load order across the condition,
allowing a CPU to predict and speculate memory reads.

Commit 324b494c28 inlined verifying a new completion with its
handling. At least one architecture was observed to access the contents
out of order, resulting in the driver using stale data for the
completion.

Add a dma read barrier before reading the completion queue entry and
after the condition its contents depend on to ensure the read order is
determinsitic.

Reported-by: John Garry <john.garry@huawei.com>
Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Tested-by: John Garry <john.garry@huawei.com>
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Keith Busch 2020-05-08 13:04:06 -07:00 committed by Christoph Hellwig
parent 59c7c3caaa
commit b69e2ef24b
1 changed files with 5 additions and 0 deletions
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5
drivers/nvme/host/pci.c
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@ -989,6 +989,11 @@ static inline int nvme_process_cq(struct nvme_queue *nvmeq)
while (nvme_cqe_pending(nvmeq)) {
found++;
/*
* load-load control dependency between phase and the rest of
* the cqe requires a full read memory barrier
*/
dma_rmb();
nvme_handle_cqe(nvmeq, nvmeq->cq_head);
nvme_update_cq_head(nvmeq);
}