[RFT PATCH 0/2] arm64: efi: Call SetVaMap() with a 1:1 mapping

[Ard Biesheuvel]

Linux on arm64 is now in the same boat as x86, where supporting laptops
that were built to run Windows and never tested beyond what is required
for the Windows Logo certification need workarounds for all kinds of
bizarre behaviors.

On Snapdragon laptops, we cannot call SetVirtualAddressMap() from the
stub, because the firmware will crash while trying to access memory via
the virtual addresses being installed, which is explicitly unsupported
by the EFI spec.

However, not calling SetVirtualAddressMap() results in other problems:
on Ampere Altra, it causes SetTime() to crash. On Surface and Flex5g
Windows-on-ARM laptops, it causes ResetSystem() to crash.

So let's try to work around this while not making too much of a mess.

First of all, install a 1:1 mapping instead of avoiding SetVaMap()
altogether - from the EFI spec pov, this should amount to the same
thing.

Then, given that we already use a SMBIOS based hack for Altra to force
the use of SetVirtualAddressMap(), let's check for Surface systems in
the same way.

Please test, and please report the SMBIOS type 1 family field for which
this workaround is needed.

Also, note that these changes will not make a difference if the
EFI_RT_PROPERTIES_TABLE lists SetVirtualAddressMap() as not implemented.

Nathan, I would appreciate it if you could give this a spin on your
Altra box (only patch #1 should make a difference), and for good
measure, double check that hwclock still works as it should.

Cc: Johan Hovold <johan+linaro at kernel.org>
Cc: Maximilian Luz <luzmaximilian at gmail.com>
Cc: Nathan Chancellor <nathan at kernel.org>
Cc: Steev Klimaszewski <steev at kali.org>
Cc: Shawn Guo <shawn.guo at linaro.org>

Ard Biesheuvel (2):
  arm64: efi: Prefer a flat virtual mapping of the runtime services
  arm64: efi: Force use of SetVirtualAddressMap() on MS Surface

 arch/arm64/include/asm/efi.h            | 2 ++
 drivers/firmware/efi/libstub/arm64.c    | 3 ++-
 drivers/firmware/efi/libstub/efi-stub.c | 6 +++++-
 3 files changed, 9 insertions(+), 2 deletions(-)

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2.39.0