[RFC PATCH 0/9] efi/x86: Avoid the need to mangle the EFI memory map

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

At boot, x86 uses E820 tables, memblock tables and the EFI memory map to
reason about which parts of system RAM are available to the OS, and
which are reserved.

While other EFI architectures treat the EFI memory map as immutable, the
x86 boot code modifies it to keep track of memory reservations of boot
services data regions, in order to distinguish which parts have been
memblock_reserve()'d permanently, and which ones have been reserved only
temporarily to work around buggy implementations of the EFI runtime
service [SetVirtualAddressMap()] that reconfigures the VA space of the
runtime services themselves.

This method is mostly fine for marking entire regions as reserved, but
it gets complicated when the code decides to split EFI memory map
entries in order to mark some of it permanently reserved, and the rest
of it temporarily reserved.

Let's clean this up, by
- marking permanent reservations of EFI boot services data memory as
  MEMBLOCK_RSRV_KERN
- taking this marking into account when deciding whether or not a EFI
  boot services data region can be freed
- dropping all of the EFI memory map insertion/splitting logic and the
  allocation/freeing logic, all of which have become redundant.

Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Ard Biesheuvel (9):
  memblock: Permit existing reserved regions to be marked RSRV_KERN
  efi: Tag memblock reservations of boot services regions as RSRV_KERN
  x86/efi: Omit RSRV_KERN memblock reservations when freeing boot
    regions
  x86/efi: Defer sub-1M check from unmap to free stage
  x86/efi: Unmap kernel-reserved boot regions from EFI page tables
  x86/efi: Do not rely on EFI_MEMORY_RUNTIME bit and avoid entry
    splitting
  x86/efi: Reuse memory map instead of reallocating it
  x86/efi: Defer compaction of the EFI memory map
  x86/efi: Free unused tail of the EFI memory map

 arch/x86/include/asm/efi.h     |   7 -
 arch/x86/platform/efi/memmap.c | 221 +------------------
 arch/x86/platform/efi/quirks.c | 222 +++++++-------------
 drivers/firmware/efi/efi.c     |   4 +-
 include/linux/efi.h            |   2 -
 include/linux/memblock.h       |   1 +
 mm/memblock.c                  |  15 ++
 7 files changed, 96 insertions(+), 376 deletions(-)

base-commit: a4b0bf6a40f3c107c67a24fbc614510ef5719980 # linux-efi/urgent
-- 
2.53.0.473.g4a7958ca14-goog