On Thu, 25 Jan 2024 at 15:37, Linus Walleij [off-list ref] wrote:

It was brought to our attention that some MMC host drivers
are referencing sg_virt(sg) directly on scatterlist entries,
which will not perform buffer bouncing for CONFIG_HIGHMEM
pages that reside in highmem.

See the following mail from Christoph and the discussion:
https://lore.kernel.org/linux-mmc/20240122073423.GA25859@lst.de/ (local)

This means that bugs with highmem pages can go unnoticed
until an actual highmem page is finally used and not bounced,
resulting in things like unpredictable file corruption.

Attempt to fix this by amending all host controllers
calling sg_virt() for PIO to instead do proper mapping
and unmapping of the scatterlist entry, possibly bouncing
it from highmem if need be.

More complicated patches are possible, the most obvious
to rewrite the PIO loops to use sg_miter_[start|next|stop]()
see for example mmci.c, but I leave this refactoring as
a suggestion to each device driver maintainer because I
can't really test the patches.

All patches are compile-tested except the m68k one,
sdhci-esdhc-mcf.

Signed-off-by: Linus Walleij <redacted>

Thanks for helping out with this! Applied for next!

Kind regards
Uffe

---
Linus Walleij (7):
      mmc: davinci_mmc: Map the virtual page for PIO
      mmc: moxart-mmc: Map the virtual page for PIO
      mmc: mvsdio: Map the virtual page for PIO
      mmc: mxcmmc: Map the virtual page for PIO
      mmc: omap: Map the virtual page for PIO
      mmc: sdhci-esdhc-mcf: Map the virtual page for swapping
      mmc: sh_mmcif: Map the virtual page for PIO

 drivers/mmc/host/davinci_mmc.c     | 10 ++++++++--
 drivers/mmc/host/moxart-mmc.c      |  3 ++-
 drivers/mmc/host/mvsdio.c          |  3 ++-
 drivers/mmc/host/mxcmmc.c          | 23 +++++++++++++++--------
 drivers/mmc/host/omap.c            |  7 ++++++-
 drivers/mmc/host/sdhci-esdhc-mcf.c |  3 ++-
 drivers/mmc/host/sh_mmcif.c        | 22 ++++++++++++++++++----
 7 files changed, 53 insertions(+), 18 deletions(-)
---
base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
change-id: 20240125-mmc-proper-kmap-f2d4cf5d1756

Best regards,
--
Linus Walleij [off-list ref]