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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Fri, 2 Jul 2021 10:19:13 +0200
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To:     Arnd Bergmann <arnd@kernel.org>,
        Shawn Lin <shawn.lin@rock-chips.com>
Cc:     Jernej Skrabec <jernej.skrabec@gmail.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        linux-mmc <linux-mmc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, 2 Jul 2021 at 09:03, Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Fri, Jul 2, 2021 at 3:02 AM Shawn Lin <shawn.lin@rock-chips.com> wrote:
> > On 2021/6/30 20:20, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@arndb.de>
> > >
> > > Jernej Skrabec reported a problem with the cw1200 driver failing on
> > > arm64 systems with CONFIG_VMAP_STACK=y.
> > >
> > > The driver in this case passes a pointer to a stack variable (in vmalloc
> > > space) into the sdio layer, which gets translated into an invalid DMA
> > > address.
> > >
> > > Even without CONFIG_VMAP_STACK, the driver is still unreliable, as
> > > cache invalidations on the DMA buffer may cause random data corruption
> > > in adjacent stack slots.
> > >
> > > This could be worked around in the SDIO core, but in the discussion we
> > > decided that passing a stack variable into SDIO should always be considered
> > > a bug, as it is for USB drivers.
> > >
> > > Change the sdio core to produce a one-time warning for any on-stack
> > > (both with and without CONFIG_VMAP_STACK) as well as any vmalloc
> > > or module-local address that would have the same translation problem.
> >
> > This was the previous comment about the same topic.
> > Should we check for mmc_io_rw_direct?
> >
> > https://www.spinics.net/lists/linux-mmc/msg41794.html
>
> Hi Shawn,
>
> thank you for remembering that previous discussion, that is a
> good question. Looking at the code though, I don't actually
> see any part of mmc_io_rw_direct() doing DMA on a caller-provided
> buffer. The only thing I see in the code is a 'u8 *out' argument, but
> that is just a pointer to a single byte that is set by this function.
>
> Do you see any other issue with that function, or does that mean
> we don't have to change it?

I was wrong when I earlier said that we needed to care about
mmc_io_rw_direct(). mmc_io_rw_direct() transfer "data" over the CMD
line. MMC host drivers can't do DMA on that.

I think the $subject patch looks reasonable to me.

Kind regards
Uffe