1 files changed, 51 insertions, 0 deletions
diff --git a/MdePkg/Include/Pi/PiMultiPhase.h b/MdePkg/Include/Pi/PiMultiPhase.h
index 1c7332e..5a22ca0 100644
--- a/MdePkg/Include/Pi/PiMultiPhase.h
+++ b/MdePkg/Include/Pi/PiMultiPhase.h
@@ -111,6 +111,14 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 #define EFI_SMRAM_LOCKED  EFI_MMRAM_LOCKED
 
 ///
+/// MM Communicate header constants
+///
+#define COMMUNICATE_HEADER_V3_GUID \
+  { \
+    0x68e8c853, 0x2ba9, 0x4dd7, { 0x9a, 0xc0, 0x91, 0xe1, 0x61, 0x55, 0xc9, 0x35 } \
+  }
+
+///
 /// Structure describing a MMRAM region and its accessibility attributes.
 ///
 typedef struct {
@@ -156,6 +164,47 @@ typedef struct _EFI_MM_RESERVED_MMRAM_REGION {
   UINT64                  MmramReservedSize;
 } EFI_MM_RESERVED_MMRAM_REGION;
 
+#pragma pack(1)
+
+///
+/// To avoid confusion in interpreting frames, the buffer communicating to MM core through
+/// EFI_MM_COMMUNICATE3 or later should always start with EFI_MM_COMMUNICATE_HEADER_V3.
+///
+typedef struct {
+  ///
+  /// Indicator GUID for MM core that the communication buffer is compliant with this v3 header.
+  /// Must be gEfiMmCommunicateHeaderV3Guid.
+  ///
+  EFI_GUID    HeaderGuid;
+  ///
+  /// Describes the size of the entire buffer (in bytes) available for communication, including this communication header.
+  ///
+  UINT64      BufferSize;
+  ///
+  /// Reserved for future use.
+  ///
+  UINT64      Reserved;
+  ///
+  /// Allows for disambiguation of the message format.
+  ///
+  EFI_GUID    MessageGuid;
+  ///
+  /// Describes the size of MessageData (in bytes) and does not include the size of the header.
+  ///
+  UINT64      MessageSize;
+  ///
+  /// Designates an array of bytes that is MessageSize in size.
+  ///
+  UINT8       MessageData[];
+} EFI_MM_COMMUNICATE_HEADER_V3;
+
+#pragma pack()
+
+STATIC_ASSERT (
+  (sizeof (EFI_MM_COMMUNICATE_HEADER_V3) == OFFSET_OF (EFI_MM_COMMUNICATE_HEADER_V3, MessageData)), \
+  "sizeof (EFI_MM_COMMUNICATE_HEADER_V3) does not align with the beginning of flexible array MessageData"
+  );
+
 typedef enum {
   EFI_PCD_TYPE_8,
   EFI_PCD_TYPE_16,
@@ -215,4 +264,6 @@ EFI_STATUS
   IN VOID  *ProcedureArgument
   );
 
+extern EFI_GUID  gEfiMmCommunicateHeaderV3Guid;
+
 #endif