diff --git a/OvmfPkg/PlatformPei/Fv.c b/OvmfPkg/PlatformPei/Fv.c
index 3ed775c850..248c585085 100644
--- a/OvmfPkg/PlatformPei/Fv.c
+++ b/OvmfPkg/PlatformPei/Fv.c
@@ -32,6 +32,8 @@ PeiFvInitialization (
   VOID
   )
 {
+  BOOLEAN SecureS3Needed;
+
   DEBUG ((EFI_D_INFO, "Platform PEI Firmware Volume Initialization\n"));
 
   //
@@ -50,15 +52,38 @@ PeiFvInitialization (
   //
   BuildFvHob (PcdGet32 (PcdOvmfDxeMemFvBase), PcdGet32 (PcdOvmfDxeMemFvSize));
 
+  SecureS3Needed = mS3Supported && FeaturePcdGet (PcdSmmSmramRequire);
+
   //
   // Create a memory allocation HOB for the DXE FV.
   //
+  // If "secure" S3 is needed, then SEC will decompress both PEI and DXE
+  // firmware volumes at S3 resume too, hence we need to keep away the OS from
+  // DXEFV as well. Otherwise we only need to keep away DXE itself from the
+  // DXEFV area.
+  //
   BuildMemoryAllocationHob (
     PcdGet32 (PcdOvmfDxeMemFvBase),
     PcdGet32 (PcdOvmfDxeMemFvSize),
-    EfiBootServicesData
+    SecureS3Needed ? EfiACPIMemoryNVS : EfiBootServicesData
     );
 
+  //
+  // Additionally, said decompression will use temporary memory above the end
+  // of DXEFV, so let's keep away the OS from there too.
+  //
+  if (SecureS3Needed) {
+    UINT32 DxeMemFvEnd;
+
+    DxeMemFvEnd = PcdGet32 (PcdOvmfDxeMemFvBase) +
+                  PcdGet32 (PcdOvmfDxeMemFvSize);
+    BuildMemoryAllocationHob (
+      DxeMemFvEnd,
+      PcdGet32 (PcdOvmfDecompressionScratchEnd) - DxeMemFvEnd,
+      EfiACPIMemoryNVS
+      );
+  }
+
   //
   // Let PEI know about the DXE FV so it can find the DXE Core
   //
diff --git a/OvmfPkg/PlatformPei/MemDetect.c b/OvmfPkg/PlatformPei/MemDetect.c
index 612bb4a3ef..5fe8b282c0 100644
--- a/OvmfPkg/PlatformPei/MemDetect.c
+++ b/OvmfPkg/PlatformPei/MemDetect.c
@@ -222,7 +222,16 @@ PublishPeiMemory (
     //
     // Determine the range of memory to use during PEI
     //
-    MemoryBase = PcdGet32 (PcdOvmfDxeMemFvBase) + PcdGet32 (PcdOvmfDxeMemFvSize);
+    // Technically we could lay the permanent PEI RAM over SEC's temporary
+    // decompression and scratch buffer even if "secure S3" is needed, since
+    // their lifetimes don't overlap. However, PeiFvInitialization() will cover
+    // RAM up to PcdOvmfDecompressionScratchEnd with an EfiACPIMemoryNVS memory
+    // allocation HOB, and other allocations served from the permanent PEI RAM
+    // shouldn't overlap with that HOB.
+    //
+    MemoryBase = mS3Supported && FeaturePcdGet (PcdSmmSmramRequire) ?
+      PcdGet32 (PcdOvmfDecompressionScratchEnd) :
+      PcdGet32 (PcdOvmfDxeMemFvBase) + PcdGet32 (PcdOvmfDxeMemFvSize);
     MemorySize = LowerMemorySize - MemoryBase;
     if (MemorySize > PeiMemoryCap) {
       MemoryBase = LowerMemorySize - PeiMemoryCap;
diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
index c2c7da94c4..4b1e68de43 100644
--- a/OvmfPkg/PlatformPei/PlatformPei.inf
+++ b/OvmfPkg/PlatformPei/PlatformPei.inf
@@ -74,6 +74,7 @@
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfLockBoxStorageSize
   gUefiOvmfPkgTokenSpaceGuid.PcdGuidedExtractHandlerTableSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfHostBridgePciDevId
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDecompressionScratchEnd
   gEfiIntelFrameworkModulePkgTokenSpaceGuid.PcdS3AcpiReservedMemorySize
   gEfiMdePkgTokenSpaceGuid.PcdGuidedExtractHandlerTableAddress
   gEfiMdeModulePkgTokenSpaceGuid.PcdVariableStoreSize
@@ -87,6 +88,9 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdPropertiesTableEnable
   gUefiCpuPkgTokenSpaceGuid.PcdCpuLocalApicBaseAddress
 
+[FeaturePcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
+
 [Ppis]
   gEfiPeiMasterBootModePpiGuid
 
diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c
index 93e3594e29..a12e6768ae 100644
--- a/OvmfPkg/Sec/SecMain.c
+++ b/OvmfPkg/Sec/SecMain.c
@@ -539,13 +539,25 @@ FindPeiCoreImageBase (
      OUT  EFI_PHYSICAL_ADDRESS             *PeiCoreImageBase
   )
 {
+  BOOLEAN S3Resume;
+
   *PeiCoreImageBase = 0;
 
-  if (IsS3Resume ()) {
+  S3Resume = IsS3Resume ();
+  if (S3Resume && !FeaturePcdGet (PcdSmmSmramRequire)) {
+    //
+    // A malicious runtime OS may have injected something into our previously
+    // decoded PEI FV, but we don't care about that unless SMM/SMRAM is required.
+    //
     DEBUG ((EFI_D_VERBOSE, "SEC: S3 resume\n"));
     GetS3ResumePeiFv (BootFv);
   } else {
-    DEBUG ((EFI_D_VERBOSE, "SEC: Normal boot\n"));
+    //
+    // We're either not resuming, or resuming "securely" -- we'll decompress
+    // both PEI FV and DXE FV from pristine flash.
+    //
+    DEBUG ((EFI_D_VERBOSE, "SEC: %a\n",
+      S3Resume ? "S3 resume (with PEI decompression)" : "Normal boot"));
     FindMainFv (BootFv);
 
     DecompressMemFvs (BootFv);
diff --git a/OvmfPkg/Sec/SecMain.inf b/OvmfPkg/Sec/SecMain.inf
index 9e8571dddd..711b595309 100644
--- a/OvmfPkg/Sec/SecMain.inf
+++ b/OvmfPkg/Sec/SecMain.inf
@@ -71,3 +71,6 @@
   gEfiMdePkgTokenSpaceGuid.PcdGuidedExtractHandlerTableAddress
   gUefiOvmfPkgTokenSpaceGuid.PcdGuidedExtractHandlerTableSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDecompressionScratchEnd
+
+[FeaturePcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire