The UEFI spec revision 2.7 errata A section 8.4 has the following to
say about the virtual memory runtime services:

  "This section contains function definitions for the virtual memory
  support that may be optionally used by an operating system at runtime.
  If an operating system chooses to make EFI runtime service calls in a
  virtual addressing mode instead of the flat physical mode, then the
  operating system must use the services in this section to switch the
  EFI runtime services from flat physical addressing to virtual
  addressing."

So it is pretty clear that calling SetVirtualAddressMap() is entirely
optional, and so there is no point in doing so unless it achieves
anything useful for us.

This is not the case for 64-bit ARM. The identity mapping used by the
firmware is arbitrarily converted into another permutation of userland
addresses (i.e., bits [63:48] cleared), and the runtime code could easily
deal with the original layout in exactly the same way as it deals with
the converted layout. However, due to constraints related to page size
differences if the OS is not running with 4k pages, and related to
systems that may expose the individual sections of PE/COFF runtime
modules as different memory regions, creating the virtual layout is a
bit fiddly, and requires us to sort the memory map and reason about
adjacent regions with identical memory types etc etc.

So the obvious fix is to stop calling SetVirtualAddressMap() altogether
on arm64 systems. However, to avoid surprises, which are notoriously
hard to diagnose when it comes to OS<->firmware interactions, let's
start by making it an opt-out feature, and implement support for the
'efi=novamap' kernel command line parameter on ARM and arm64 systems.

( Note that 32-bit ARM generally does require SetVirtualAddressMap() to be
  used, given that the physical memory map and the kernel virtual address
  map are not guaranteed to be non-overlapping like on arm64. However,
  having support for efi=novamap,noruntime on 32-bit ARM, combined with
  the recently proposed support for earlycon=efifb, is likely to be useful
  to diagnose boot issues on such systems if they have no accessible serial
  port. )
Tested-by: Jeffrey Hugo <jhugo@codeaurora.org>
Tested-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Alexander Graf <agraf@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Jones <pjones@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20190202094119.13230-8-ard.biesheuvel@linaro.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>