Re: [PATCH v3 2/7] MdePkg: MmCommunication: Introduce EFI_MM_COMMUNICATE_HEADER_V3 to MdePkg

Kun Qin

Hi Ray,

This same header will be commonly used for both MM communicate PPI and Protocol. If including this definition in MmCommunicate protocol header, the potential PEIM that installs MM communicate PPI will need to include a PPI header as well as the aforementioned protocol header, which to me seems counter-intuitive.

I think PiMultiPhase header seems to be a file more ideal to resolve the entanglement above, as this structure indeed covers multiple phases during boot process.

Please let me know if you have any other thoughts.


On 08/16/2021 22:50, Ni, Ray wrote:
Can you kindly explain why you choose to define the definitions in PiMultiPhase.h instead of MmCommunication.h?

-----Original Message-----
From: <> On Behalf Of Kun Qin
Sent: Tuesday, August 17, 2021 1:08 PM
Cc: Kinney, Michael D <michael.d.kinney@...>; Liming Gao <gaoliming@...>; Liu, Zhiguang
<zhiguang.liu@...>; Wu, Hao A <hao.a.wu@...>; Marvin Häuser <mhaeuser@...>; Bret Barkelew
<Bret.Barkelew@...>; Michael Kubacki <michael.kubacki@...>
Subject: [edk2-devel] [PATCH v3 2/7] MdePkg: MmCommunication: Introduce EFI_MM_COMMUNICATE_HEADER_V3 to


This change introduces a new definition for MM communicate header
structure, intending to provide better portability between different
architectures (IA32 & X64) and adapt to flexible array supported by
modern compilers.

The original MessageLength field of EFI_MM_COMMUNICATE_HEADER, as a
generic definition, was used for both PEI and DXE MM communication. On a
system that supports PEI MM launch, but operates PEI in 32bit mode and MM
foundation in 64bit, the current EFI_MM_COMMUNICATE_HEADER definition
will cause structure parse error due to UINTN used. This introduction
removes the architecture dependent field by defining this field as

The new signature could help identifying whether the data received is
compiliant with this new data structure, which will help for binary
release modules to identify usage of legacy data structure.

Version field is also added to indicate the current version of header in
case there is need for minor modification in the future.

The data field of MM communicate message is replaced with flexible array
to allow users not having to consume extra data during communicate and
author code more intrinsically.

Cc: Michael D Kinney <michael.d.kinney@...>
Cc: Liming Gao <gaoliming@...>
Cc: Zhiguang Liu <zhiguang.liu@...>
Cc: Hao A Wu <hao.a.wu@...>
Cc: Marvin Häuser <mhaeuser@...>
Cc: Bret Barkelew <Bret.Barkelew@...>
Cc: Michael Kubacki <michael.kubacki@...>

Signed-off-by: Kun Qin <kuqin12@...>

- Newly introduced communicate v3
- Used flexible arrays [Marvin]
- Added static assert [Michael]

MdePkg/Include/Pi/PiMultiPhase.h | 55 ++++++++++++++++++++
MdePkg/MdePkg.dec | 5 ++
2 files changed, 60 insertions(+)

diff --git a/MdePkg/Include/Pi/PiMultiPhase.h b/MdePkg/Include/Pi/PiMultiPhase.h
index 89280d9d3506..8c60338091b3 100644
--- a/MdePkg/Include/Pi/PiMultiPhase.h
+++ b/MdePkg/Include/Pi/PiMultiPhase.h
@@ -103,6 +103,17 @@ SPDX-License-Identifier: BSD-2-Clause-Patent

+/// MM Communicate header constants
+ { \
+ 0x68e8c853, 0x2ba9, 0x4dd7, { 0x9a, 0xc0, 0x91, 0xe1, 0x61, 0x55, 0xc9, 0x35 } \
+ }
/// Structure describing a MMRAM region and its accessibility attributes.
@@ -149,6 +160,48 @@ typedef struct _EFI_MM_RESERVED_MMRAM_REGION {
UINT64 MmramReservedSize;

+#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 gCommunicateHeaderV3Guid.
+ ///
+ EFI_GUID HeaderGuid;
+ ///
+ /// Signature to indicate data is compliant with new MM communicate header structure.
+ /// Must be "MCH3".
+ ///
+ UINT32 Signature;
+ ///
+ /// MM communicate data format version, MM foundation entry point should check if incoming
+ /// data is a supported format before proceeding.
+ /// Must be 3.
+ ///
+ UINT32 Version;
+ ///
+ /// 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[];
+#pragma pack()
MessageData)), \
+ "sizeof (EFI_MM_COMMUNICATE_HEADER_V3) does not align with the beginning of flexible array MessageData");
typedef enum {
@@ -208,4 +261,6 @@ EFI_STATUS
IN VOID *ProcedureArgument

+extern EFI_GUID gCommunicateHeaderV3Guid;
diff --git a/MdePkg/MdePkg.dec b/MdePkg/MdePkg.dec
index a28a2daaffa8..411079a4343e 100644
--- a/MdePkg/MdePkg.dec
+++ b/MdePkg/MdePkg.dec
@@ -823,6 +823,11 @@ [Guids]
gLinuxEfiInitrdMediaGuid = {0x5568e427, 0x68fc, 0x4f3d, {0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68}}

+ #
+ # GUID indicates the MM communication data is compliant with v3 communication header.
+ #
+ gCommunicateHeaderV3Guid = { 0x68e8c853, 0x2ba9, 0x4dd7, { 0x9a, 0xc0, 0x91, 0xe1, 0x61, 0x55, 0xc9, 0x35 } }
[Guids.IA32, Guids.X64]
## Include/Guid/Cper.h
gEfiIa32X64ErrorTypeCacheCheckGuid = { 0xA55701F5, 0xE3EF, 0x43de, { 0xAC, 0x72, 0x24, 0x9B, 0x57, 0x3F, 0xAD, 0x2C }}

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