[PATCH 4/4] efi/arm64: unmap the kernel while executing UEFI services

[Will Deacon]

On Thu, Jan 25, 2018 at 10:31:31AM +0000, Ard Biesheuvel wrote:
> Now that all UEFI runtime service wrappers ensure that byref
> arguments are moved into the UEFI marshalling buffer (which
> is not part of the kernel mapping), we can proceed and unmap
> the kernel while UEFI runtime service calls are in progress.
> 
> This is done by setting the EPD1 bit and flushing the TLB of
> the local CPU. This makes it independent of KPTI or whether
> non-global mappings are being used.

One snag with this is that it will break SPE, so I'd prefer this behaviour
to be predicated on kpti so that the arm64_kernel_unmapped_at_el0() check
in drivers/perf/arm_spe_pmu.c remains valid.

Will