[PATCH v4 0/6] arm64: efi: leave MMU and caches on at boot

[Ard Biesheuvel]

The purpose of this series is to remove any explicit cache maintenance
for coherency during early boot that becomes unnecessary if we simply
retain the cacheable 1:1 mapping of all of system RAM provided by EFI,
and use it to populate the ID map page tables. After setting up this
preliminary ID map, we disable the MMU, drop to EL1, reprogram the MAIR,
TCR and SCTLR registers as before, and proceed as usual, avoiding the
need for any manipulations of memory while the MMU and caches are off.

The only properties of the firmware provided 1:1 map we rely on is that
it does not require any explicit cache maintenance for coherency, and
that it covers the entire memory footprint of the image, including the
BSS and padding at the end - all else is under control of the kernel
itself, as before.

Changes since v3:
- drop EFI_LOADER_CODE memory type patch that has been queued in the
  mean time
- rebased onto [partial] series that moves efi-entry.S into the libstub/
  source directory [0]
- fixed a correctness issue in patch #2

[0] https://lore.kernel.org/all/20221017171700.3736890-1-ardb@kernel.org/

Applying the last patch in the series will require some coordination
with the EFI tree, but I can manage that using a secondary 'late' PR
during the merge window, if needed.

Cc: Will Deacon <will at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>

Ard Biesheuvel (6):
  arm64: lds: reduce effective minimum image alignment to 64k
  arm64: kernel: move identity map out of .text mapping
  arm64: head: record the MMU state at primary entry
  arm64: head: avoid cache invalidation when entering with the MMU on
  arm64: head: clean the ID map page to the PoC
  arm64: efi/libstub: enter with the MMU on

 arch/arm64/include/asm/efi.h               |  7 --
 arch/arm64/kernel/head.S                   | 70 +++++++++++++++-----
 arch/arm64/kernel/image-vars.h             |  5 +-
 arch/arm64/kernel/vmlinux.lds.S            | 13 +++-
 arch/arm64/mm/cache.S                      |  5 +-
 arch/arm64/mm/proc.S                       |  2 -
 drivers/firmware/efi/libstub/arm64-entry.S | 57 ----------------
 drivers/firmware/efi/libstub/arm64-stub.c  | 19 +++++-
 include/linux/efi.h                        |  6 +-
 9 files changed, 89 insertions(+), 95 deletions(-)
 delete mode 100644 drivers/firmware/efi/libstub/arm64-entry.S

-- 
2.35.1