StandaloneMmPkg: Introduce a PCD to disable shadow boot FV

On some Arm platforms the boot firmware volume passed in the HOB by the secure world firmware (TF-A) is never freed and is always mapped as read-only. On such platforms the heap memory can be saved by disabling the shadow copy of the boot firmware volume. This is useful as on some platforms the amount of memory available is limited. Therefore, introduce a PCD PcdDisableShadowBfv that platforms can configure to disable the shadow boot FV. This PCD is set to FALSE by default. Signed-off-by: Levi Yun <[email protected]>
tianocore · Jan 17, 2025 · c445148 · c445148
1 parent f0c87b9
commit c445148
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Showing 3 changed files with 40 additions and 10 deletions.
diff --git a/StandaloneMmPkg/Core/FwVol.c b/StandaloneMmPkg/Core/FwVol.c
@@ -270,18 +270,36 @@ MmDispatchFvs (
 
     DEBUG ((DEBUG_INFO, "%a: FV[%d] address - 0x%x\n", __func__, Index, FvHob.FirmwareVolume->BaseAddress));
     DEBUG ((DEBUG_INFO, "%a: FV[%d] size    - 0x%x\n", __func__, Index, FvHob.FirmwareVolume->Length));
-    Fv = AllocatePool (FvHob.FirmwareVolume->Length);
-    if (Fv == NULL) {
-      DEBUG ((DEBUG_ERROR, "Fail to allocate memory for Fv\n"));
-      CpuDeadLoop ();
-      return;
+
+    if (FvHob.FirmwareVolume->Length == 0x00) {
+      DEBUG ((
+        DEBUG_INFO,
+        "%a: Skip invalid FV[%d]- 0x%x/0x%x\n",
+        __func__,
+        Index,
+        FvHob.FirmwareVolume->BaseAddress,
+        FvHob.FirmwareVolume->Length
+        ));
+      continue;
+    }
+
+    if (FixedPcdGetBool (PcdDisableShadowBfv)) {
+      Fv = (EFI_FIRMWARE_VOLUME_HEADER *)FvHob.FirmwareVolume->BaseAddress;
+    } else {
+      Fv = AllocatePool (FvHob.FirmwareVolume->Length);
+      if (Fv == NULL) {
+        DEBUG ((DEBUG_ERROR, "Fail to allocate memory for Fv\n"));
+        CpuDeadLoop ();
+        return;
+      }
+
+      CopyMem (
+        (VOID *)Fv,
+        (VOID *)(UINTN)FvHob.FirmwareVolume->BaseAddress,
+        FvHob.FirmwareVolume->Length
+        );
     }
 
-    CopyMem (
-      (VOID *)Fv,
-      (VOID *)(UINTN)FvHob.FirmwareVolume->BaseAddress,
-      FvHob.FirmwareVolume->Length
-      );
     MmCoreFfsFindMmDriver (Fv, 0);
     mMmFv[Index++] = Fv;
 
@@ -307,6 +325,10 @@ MmFreeShadowedFvs (
 {
   UINTN  Index;
 
+  if (FixedPcdGetBool (PcdDisableShadowBfv)) {
+    return;
+  }
+
   for (Index = 0; Index < ARRAY_SIZE (mMmFv); Index++) {
     if (mMmFv[Index] != NULL) {
       FreePool (mMmFv[Index]);

diff --git a/StandaloneMmPkg/Core/StandaloneMmCore.inf b/StandaloneMmPkg/Core/StandaloneMmCore.inf
@@ -85,6 +85,7 @@
 [Pcd]
   gStandaloneMmPkgTokenSpaceGuid.PcdFwVolMmMaxEncapsulationDepth    ##CONSUMES
   gStandaloneMmPkgTokenSpaceGuid.PcdRestartMmDispatcherOnceMmEntryRegistered    ##CONSUMES
+  gStandaloneMmPkgTokenSpaceGuid.PcdDisableShadowBfv    ##CONSUMES
 
 #
 # This configuration fails for CLANGPDB, which does not support PIE in the GCC

diff --git a/StandaloneMmPkg/StandaloneMmPkg.dec b/StandaloneMmPkg/StandaloneMmPkg.dec
@@ -55,6 +55,13 @@
   # @Prompt Maximum permitted FwVol section nesting depth (exclusive) in MM.
   gStandaloneMmPkgTokenSpaceGuid.PcdFwVolMmMaxEncapsulationDepth|0x10|UINT32|0x00000001
 
+  ## Option to disable shadow copy of boot firmware volume while loading drivers.
+  #  This options is useful when the BFV is not located in the Flash area
+  #  but is in the RAM instead and therefore no shadow copy is needed.
+  #   TRUE  - Disable shadow copy of the boot firmware volume.
+  #   FALSE - Default. Make a shadow copy of the boot firmware volume.
+  gStandaloneMmPkgTokenSpaceGuid.PcdDisableShadowBfv|FALSE|BOOLEAN|0x00000003
+
 [PcdsFeatureFlag]
   ## Indicates if restart MM Dispatcher once MM Entry Point is registered.<BR><BR>
   #   TRUE  - Restart MM Dispatcher once MM Entry Point is registered.<BR>