Re: [PATCH V8 5/5] libata: Align DMA buffer todma_get_cache_alignment()

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Hi, Sergei,

Without this patch, in non-coherent mode, ata_do_set_mode() return with "no PIO support", and disk detection fails.

Huacai
 
 
------------------ Original ------------------
From:  "Sergei Shtylyov"<sergei.shtylyov@xxxxxxxxxxxxxxxxxx>;
Date:  Tue, Oct 17, 2017 05:43 PM
To:  "Huacai Chen"<chenhc@xxxxxxxxxx>; "Christoph Hellwig"<hch@xxxxxx>; 
Cc:  "Marek Szyprowski"<m.szyprowski@xxxxxxxxxxx>; "Robin Murphy"<robin.murphy@xxxxxxx>; "Andrew Morton"<akpm@xxxxxxxxxxxxxxxxxxxx>; "Fuxin Zhang"<zhangfx@xxxxxxxxxx>; "linux-kernel"<linux-kernel@xxxxxxxxxxxxxxx>; "Ralf Baechle"<ralf@xxxxxxxxxxxxxx>; "James Hogan"<james.hogan@xxxxxxxxxx>; "linux-mips"<linux-mips@xxxxxxxxxxxxxx>; "James E . J . Bottomley"<jejb@xxxxxxxxxxxxxxxxxx>; "Martin K . Petersen"<martin.petersen@xxxxxxxxxx>; "linux-scsi"<linux-scsi@xxxxxxxxxxxxxxx>; "Tejun Heo"<tj@xxxxxxxxxx>; "linux-ide"<linux-ide@xxxxxxxxxxxxxxx>; "stable"<stable@xxxxxxxxxxxxxxx>; 
Subject:  Re: [PATCH V8 5/5] libata: Align DMA buffer todma_get_cache_alignment()

 
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@xxxxxxxxxxxxxxx
> Signed-off-by: Huacai Chen <chenhc@xxxxxxxxxx>
> ---
>   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