The RestoreLockBox() and RestoreAllLockBoxInPlace() functions handle the
case when EFI_PEI_SMM_COMMUNICATION_PPI.Communicate() returns
EFI_NOT_STARTED: they access the SMRAM directly, for restoring LockBox
data.
This occurs if a PEIM needs to restore LockBox data *before* the SMBASE is
relocated and the SMI handler is installed for all processors.
One such PEIM is UefiCpuPkg/Universal/Acpi/S3Resume2Pei. On the S3 resume
path, in function S3RestoreConfig2(), LockBox data are restored *before*
the SmmRestoreCpu() function of UefiCpuPkg/PiSmmCpuDxeSmm is called via
SmmS3ResumeState->SmmS3ResumeEntryPoint. (The latter SmmRestoreCpu()
function is responsible for the SMBASE relocation.)
If a platform knows that its PEIMs restore LockBox data *only* before
SMBASE relocation -- e.g., due to S3Resume2Pei being the platform's only
SmmLockBoxPeiLib client --, then the platform might not want to include
"UefiCpuPkg/PiSmmCommunication/PiSmmCommunicationPei.inf" at all (hence
not provide EFI_PEI_SMM_COMMUNICATION_PPI) -- because all of those
restores would be serviced by direct SMRAM access anyway.
Currently the absence of EFI_PEI_SMM_COMMUNICATION_PPI is not supported by
SmmLockBoxPeiLib, but it's not hard to implement. Handle it the same as
when EFI_PEI_SMM_COMMUNICATION_PPI.Communicate() returns EFI_NOT_STARTED:
restore LockBox data directly from SMRAM.
Suggested-by: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18823 6f19259b-4bc3-4df7-8a09-765794883524
Laszlo Ersek
jljusten