[coreboot-gerrit] Change in coreboot[master]: cpu/x86/smm: Add support for long mode

[Patrick Rudolph (Code Review)]

Hello build bot (Jenkins), Raul Rangel, Patrick Georgi, Patrick Rudolph, Stefan Reinauer, Paul Menzel, Angel Pons, Arthur Heymans, Aaron Durbin, Martin Roth, Lee Leahy, David Hendricks, ron minnich, Rudolf Marek,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/35681

to look at the new patch set (#17).

Change subject: cpu/x86/smm: Add support for long mode
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cpu/x86/smm: Add support for long mode

Enable long mode in SMM handler.
x86_32 isn't affected by this change.

As the rsm instruction used to leave SMM doesn't restore MSR registers,
drop back to protected mode after running the smi_handler and restore
IA32_EFER MSR (which enables long mode support) to previous value.

NOTE: This commit does NOT introduce a new security model. It uses the
      same page tables as the remaining firmware does.
      This can be a security risk if someone is able to manipulate the
      page tables stored in ROM at runtime. USE FOR TESTING ONLY!

Tested on Qemu Q35.

Change-Id: I8bba4af4688c723fc079ae905dac95f57ea956f8
Signed-off-by: Patrick Rudolph 
---
M Documentation/arch/x86/index.md
A src/cpu/x86/64bit/exit32.inc
M src/cpu/x86/smm/smmhandler.S
3 files changed, 130 insertions(+), 1 deletion(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/81/35681/17