OvmfPkg/PlatformPei: create one memory HOB at S3 resume too, for CpuMpPei

CpuMpPei will have to place the AP startup vector in memory under 1MB. For
this, CpuMpPei borrows memory under 1MB, but it needs a memory resource
descriptor HOB to exist there even on the S3 resume path (see the
GetWakeupBuffer() function). Produce such a HOB as an exception on the S3
resume path.

CpuMpPei is going be dispatched no earlier than PlatformPei, because
CpuMpPei has a depex on gEfiPeiMemoryDiscoveredPpiGuid, and PlatformPei
calls PublishSystemMemory().

Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

diff --git a/OvmfPkg/PlatformPei/MemDetect.c b/OvmfPkg/PlatformPei/MemDetect.c
index 7991ba29d7aa89534f89cb65a4c6f37c3a2a99be..d59b461547c58a6f8cea15a521f7fa6002679426 100644 (file)
--- a/OvmfPkg/PlatformPei/MemDetect.c
+++ b/OvmfPkg/PlatformPei/MemDetect.c
@@ -404,7 +404,29 @@ QemuInitializeRam (
   LowerMemorySize = GetSystemMemorySizeBelow4gb ();\r
   UpperMemorySize = GetSystemMemorySizeAbove4gb ();\r
 \r
-  if (mBootMode != BOOT_ON_S3_RESUME) {\r
+  if (mBootMode == BOOT_ON_S3_RESUME) {\r
+    //\r
+    // Create the following memory HOB as an exception on the S3 boot path.\r
+    //\r
+    // Normally we'd create memory HOBs only on the normal boot path. However,\r
+    // CpuMpPei specifically needs such a low-memory HOB on the S3 path as\r
+    // well, for "borrowing" a subset of it temporarily, for the AP startup\r
+    // vector.\r
+    //\r
+    // CpuMpPei saves the original contents of the borrowed area in permanent\r
+    // PEI RAM, in a backup buffer allocated with the normal PEI services.\r
+    // CpuMpPei restores the original contents ("returns" the borrowed area) at\r
+    // End-of-PEI. End-of-PEI in turn is emitted by S3Resume2Pei before\r
+    // transfering control to the OS's wakeup vector in the FACS.\r
+    //\r
+    // We expect any other PEIMs that "borrow" memory similarly to CpuMpPei to\r
+    // restore the original contents. Furthermore, we expect all such PEIMs\r
+    // (CpuMpPei included) to claim the borrowed areas by producing memory\r
+    // allocation HOBs, and to honor preexistent memory allocation HOBs when\r
+    // looking for an area to borrow.\r
+    //\r
+    AddMemoryRangeHob (0, BASE_512KB + BASE_128KB);\r
+  } else {\r
     //\r
     // Create memory HOBs\r
     //\r