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

[Patrick Rudolph (Code Review)]

Patrick Rudolph has uploaded a new patch set (#15) to the change originally created by Patrick Rudolph. ( https://review.coreboot.org/c/coreboot/+/35681 )

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 from 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.

For now the same page tables as for all other stages are used.
If there's enough space in SMM, one could install additional page tables in
SMRAM to enable additional features.

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, 127 insertions(+), 1 deletion(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/81/35681/15