diff options
| -rw-r--r-- | OvmfPkg/PlatformPei/MemDetect.c | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/OvmfPkg/PlatformPei/MemDetect.c b/OvmfPkg/PlatformPei/MemDetect.c index 7991ba29d7..d59b461547 100644 --- a/OvmfPkg/PlatformPei/MemDetect.c +++ b/OvmfPkg/PlatformPei/MemDetect.c @@ -404,7 +404,29 @@ QemuInitializeRam ( LowerMemorySize = GetSystemMemorySizeBelow4gb ();
UpperMemorySize = GetSystemMemorySizeAbove4gb ();
- if (mBootMode != BOOT_ON_S3_RESUME) {
+ if (mBootMode == BOOT_ON_S3_RESUME) {
+ //
+ // Create the following memory HOB as an exception on the S3 boot path.
+ //
+ // Normally we'd create memory HOBs only on the normal boot path. However,
+ // CpuMpPei specifically needs such a low-memory HOB on the S3 path as
+ // well, for "borrowing" a subset of it temporarily, for the AP startup
+ // vector.
+ //
+ // CpuMpPei saves the original contents of the borrowed area in permanent
+ // PEI RAM, in a backup buffer allocated with the normal PEI services.
+ // CpuMpPei restores the original contents ("returns" the borrowed area) at
+ // End-of-PEI. End-of-PEI in turn is emitted by S3Resume2Pei before
+ // transfering control to the OS's wakeup vector in the FACS.
+ //
+ // We expect any other PEIMs that "borrow" memory similarly to CpuMpPei to
+ // restore the original contents. Furthermore, we expect all such PEIMs
+ // (CpuMpPei included) to claim the borrowed areas by producing memory
+ // allocation HOBs, and to honor preexistent memory allocation HOBs when
+ // looking for an area to borrow.
+ //
+ AddMemoryRangeHob (0, BASE_512KB + BASE_128KB);
+ } else {
//
// Create memory HOBs
//
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