Re: [PATCH] mmc: sd: Meet alignment requirements for raw_ssr DMA

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+stable, Lars, Maarten

On 11 November 2016 at 15:22, Paul Burton <paul.burton@xxxxxxxxxx> wrote:
> The mmc_read_ssr() function results in DMA to the raw_ssr member of
> struct mmc_card, which is not guaranteed to be cache line aligned & thus
> might not meet the requirements set out in Documentation/DMA-API.txt:
>
>   Warnings:  Memory coherency operates at a granularity called the cache
>   line width.  In order for memory mapped by this API to operate
>   correctly, the mapped region must begin exactly on a cache line
>   boundary and end exactly on one (to prevent two separately mapped
>   regions from sharing a single cache line).  Since the cache line size
>   may not be known at compile time, the API will not enforce this
>   requirement.  Therefore, it is recommended that driver writers who
>   don't take special care to determine the cache line size at run time
>   only map virtual regions that begin and end on page boundaries (which
>   are guaranteed also to be cache line boundaries).
>
> On some systems where DMA is non-coherent this can lead to us losing
> data that shares cache lines with the raw_ssr array.
>
> Fix this by kmalloc'ing a temporary buffer to perform DMA into. kmalloc
> will ensure the buffer is suitably aligned, allowing the DMA to be
> performed without any loss of data.
>
> Signed-off-by: Paul Burton <paul.burton@xxxxxxxxxx>
> Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> Cc: linux-mmc@xxxxxxxxxxxxxxx

Sorry for the delay!

I dropped these Cc, but added the below tags instead.

Fixes: 5275a652d296 ("mmc: sd: Export SD Status via “ssr” device attribute")
Cc: <stable@xxxxxxxxxxxxxxx>

Thanks, applied for fixes!

Kind regards
Uffe

> ---
>  drivers/mmc/core/sd.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> index 73c762a..f6f40a1 100644
> --- a/drivers/mmc/core/sd.c
> +++ b/drivers/mmc/core/sd.c
> @@ -223,6 +223,7 @@ static int mmc_decode_scr(struct mmc_card *card)
>  static int mmc_read_ssr(struct mmc_card *card)
>  {
>         unsigned int au, es, et, eo;
> +       u32 *raw_ssr;
>         int i;
>
>         if (!(card->csd.cmdclass & CCC_APP_SPEC)) {
> @@ -231,14 +232,21 @@ static int mmc_read_ssr(struct mmc_card *card)
>                 return 0;
>         }
>
> -       if (mmc_app_sd_status(card, card->raw_ssr)) {
> +       raw_ssr = kmalloc(sizeof(card->raw_ssr), GFP_KERNEL);
> +       if (!raw_ssr)
> +               return -ENOMEM;
> +
> +       if (mmc_app_sd_status(card, raw_ssr)) {
>                 pr_warn("%s: problem reading SD Status register\n",
>                         mmc_hostname(card->host));
> +               kfree(raw_ssr);
>                 return 0;
>         }
>
>         for (i = 0; i < 16; i++)
> -               card->raw_ssr[i] = be32_to_cpu(card->raw_ssr[i]);
> +               card->raw_ssr[i] = be32_to_cpu(raw_ssr[i]);
> +
> +       kfree(raw_ssr);
>
>         /*
>          * UNSTUFF_BITS only works with four u32s so we have to offset the
> --
> 2.10.2
>
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