Allow the trampoline to use EFI boot services RAM

As currently configured, my laptop cannot boot any existing kernel because the real mode trampoline can't be reserved. The ranges in which it could live are rejected by the kernel: one is EFI boot services data and the other is above the EBDA.

Allowing use of RAM between the EBDA and 640k is scary: there are probably many quirky BIOSes out there, and, as currently structured, it would be awkward to allow it just on EFI boots because we currently reserve that range before we figure out whether we're using EFI.

This series fixes it the other way: it allow the trampoline to live in boot services memory. It achieves this by deferring the panic due to failure to reserve a trampoline until early_initcall time and then adjusting the EFI boot services quirk to reserve space for the trampoline if we haven't already found it a home.

I'm hoping this is okay for 4.8 even though it's late: it fixes a boot failure and it's fairly conservative -- the only significant changes in behavior should be on systems that currently fail to boot.

I'm not currently proposing it for stable because AFAIK I'm the only person to have seen this issue. If it survives in Linus' tree for a while, though, I might propose it for -stable later on.

Andy Lutomirski (4):
x86/boot: Synchronize trampoline_cr4_features and mmu_cr4_features
directly
x86/boot: Defer setup_real_mode() to early_initcall time x86/boot: Rework reserve_real_mode() to allow multiple tries x86/efi: Allocate a trampoline if needed in efi_free_boot_services()

Changes from v1:
- Fix comment in the last patch (hpa)
- Add missing first patch (I can't count...)
- Rebase to v4.8-rc1, uneventfully

Andy Lutomirski (5):
x86/boot: Run reserve_bios_regions() after we initialize the memory
map
x86/boot: Synchronize trampoline_cr4_features and mmu_cr4_features
directly
x86/boot: Defer setup_real_mode() to early_initcall time x86/boot: Rework reserve_real_mode() to allow multiple tries x86/efi: Allocate a trampoline if needed in efi_free_boot_services()

 arch/x86/include/asm/realmode.h | 10 ++++++++-
 arch/x86/kernel/head32.c        |  2 --
 arch/x86/kernel/head64.c        |  1 -
 arch/x86/kernel/setup.c         | 19 ++++++++++-------
 arch/x86/platform/efi/quirks.c  | 21 ++++++++++++++++++
 arch/x86/realmode/init.c        | 47 ++++++++++++++++++++++++++++++-----------
 6 files changed, 76 insertions(+), 24 deletions(-)

2.7.4