MdePkg: Avoid hardcoded value for number of Page State Change entries

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4654

The SNP_PAGE_STATE_MAX_ENTRY is based on the number of entries that can
fit in the GHCB shared buffer. As a result, the SNP_PAGE_STATE_CHANGE_INFO
structure maps the full GHCB shared buffer based on the shared buffer size
being 2032 bytes.

Instead of using a hardcoded value for SNP_PAGE_STATE_MAX_ENTRY, use a
build calculated value. Since the SNP_PAGE_STATE_CHANGE_INFO is used as a
mapping, eliminate the hardcoded array size so that the structure can be
used based on any size buffer.

Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/MdePkg/Include/Register/Amd/Ghcb.h b/MdePkg/Include/Register/Amd/Ghcb.h
index bd7bf986d0..ae1486b526 100644
--- a/MdePkg/Include/Register/Amd/Ghcb.h
+++ b/MdePkg/Include/Register/Amd/Ghcb.h
@@ -197,13 +197,14 @@ typedef struct {
   UINT32    Reserved;

 } SNP_PAGE_STATE_HEADER;

 

-#define SNP_PAGE_STATE_MAX_ENTRY  253

-

 typedef struct {

   SNP_PAGE_STATE_HEADER    Header;

-  SNP_PAGE_STATE_ENTRY     Entry[SNP_PAGE_STATE_MAX_ENTRY];

+  SNP_PAGE_STATE_ENTRY     Entry[];

 } SNP_PAGE_STATE_CHANGE_INFO;

 

+#define SNP_PAGE_STATE_MAX_ENTRY  \

+  ((sizeof (((GHCB *)0)->SharedBuffer) - sizeof (SNP_PAGE_STATE_HEADER)) / sizeof (SNP_PAGE_STATE_ENTRY))

+

 //

 // Get APIC IDs

 //