UefiCpuPkg/MtrrLib: MtrrLibIsMtrrSupported always return FALSE in TD-…

…Guest

Currently, TDX exposes MTRR CPUID bit to TDX VM. So based on the CPUID,
the guest software components (OVMF/TDVF and guest kernel) will access
MTRR MSRs. One problem for guest to use of MTRR is the change of MTRR
setting needs to set CR0.CD=1, which will case #VE for TDX.

For Linux kernel, there is a mechanism called SW defined MTRR introduced
by the patch https://lore.kernel.org/all/20230502120931.
[email protected]/. If this is integrated for TDX guest, then Linux
kernel will not access any MTRR MSRs.

So we update MtrrLibIsMtrrSupported() to always return false for TD-Guest,
then TDVF will not access MTRR MSRs at all.

Cc: Ray Ni <[email protected]>
Cc: Rahul Kumar <[email protected]>
Cc: Gerd Hoffmann <[email protected]>
Cc: Jiaxin Wu <[email protected]>
Cc: Jiewen Yao <[email protected]>
Cc: Binbin Wu <[email protected]>
Signed-off-by: Min Xu <[email protected]>

UefiCpuPkg/Library/MtrrLib/MtrrLib.c

@@ -161,6 +161,13 @@ MtrrLibIsMtrrSupported (
   CPUID_VERSION_INFO_EDX     Edx;
   MSR_IA32_MTRRCAP_REGISTER  MtrrCap;
 
+  //
+  // MTRR is not supported in TD-Guest.
+  //
+  if (TdIsEnabled ()) {
+    return FALSE;
+  }
+
   //
   // Check CPUID(1).EDX[12] for MTRR capability
   //