linux-kernel - [PATCH V6 3/3] scsi: Align block queue to dma_get_cache

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Message-Id: <1505811161-25246-3-git-send-email-chenhc@lemote.com>
Date:   Tue, 19 Sep 2017 16:52:41 +0800
From:   Huacai Chen <chenhc@...ote.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fuxin Zhang <zhangfx@...ote.com>, linux-kernel@...r.kernel.org,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, Huacai Chen <chenhc@...ote.com>,
        stable@...r.kernel.org
Subject: [PATCH V6 3/3] scsi: Align block queue to dma_get_cache_alignment()

In non-coherent DMA mode, kernel uses cache flushing operations to
maintain I/O coherency, so scsi's block queue should be aligned to
ARCH_DMA_MINALIGN. Otherwise, it will cause data corruption, at least
on MIPS:

        Step 1, dma_map_single
        Step 2, cache_invalidate (no writeback)
        Step 3, dma_from_device
        Step 4, dma_unmap_single

If a DMA buffer and a kernel structure share a same cache line, and if
the kernel structure has dirty data, cache_invalidate (no writeback)
will cause data lost.

Cc: stable@...r.kernel.org
Signed-off-by: Huacai Chen <chenhc@...ote.com>
---
 drivers/scsi/scsi_lib.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 9cf6a80..19abc2e 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2132,11 +2132,11 @@ void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
 		q->limits.cluster = 0;
 
 	/*
-	 * set a reasonable default alignment on word boundaries: the
-	 * host and device may alter it using
+	 * set a reasonable default alignment on word/cacheline boundaries:
+	 * the host and device may alter it using
 	 * blk_queue_update_dma_alignment() later.
 	 */
-	blk_queue_dma_alignment(q, 0x03);
+	blk_queue_dma_alignment(q, max(4, dma_get_cache_alignment(dev)) - 1);
 }
 EXPORT_SYMBOL_GPL(__scsi_init_queue);
 
-- 
2.7.0