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SubjectRe: [PATCH V8 5/5] libata: Align DMA buffer to dma_get_cache_alignment()
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On 10/17/2017 11:05 AM, Huacai Chen wrote:

> In non-coherent DMA mode, kernel uses cache flushing operations to
> maintain I/O coherency, so in ata_do_dev_read_id() the DMA buffer
> should be aligned to ARCH_DMA_MINALIGN. Otherwise, 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 corruption.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Huacai Chen <chenhc@lemote.com>
> ---
> drivers/ata/libata-core.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index ee4c1ec..e134955 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -1833,8 +1833,19 @@ static u32 ata_pio_mask_no_iordy(const struct ata_device *adev)
> unsigned int ata_do_dev_read_id(struct ata_device *dev,
> struct ata_taskfile *tf, u16 *id)
> {
> - return ata_exec_internal(dev, tf, NULL, DMA_FROM_DEVICE,
> - id, sizeof(id[0]) * ATA_ID_WORDS, 0);
> + u16 *devid;
> + int res, size = sizeof(u16) * ATA_ID_WORDS;
> +
> + if (IS_ALIGNED((unsigned long)id, dma_get_cache_alignment(&dev->tdev)))
> + res = ata_exec_internal(dev, tf, NULL, DMA_FROM_DEVICE, id, size, 0);
> + else {
> + devid = kmalloc(size, GFP_KERNEL);
> + res = ata_exec_internal(dev, tf, NULL, DMA_FROM_DEVICE, devid, size, 0);
> + memcpy(id, devid, size);
> + kfree(devid);
> + }
> +
> + return res;

This function is called only for the PIO mode commands, so I doubt this is
necessary...

MBR, Sergei

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