[PATCH v2 2/2] UefiCpuPkg/PiSmmCpu: PcdCpuSmmAccessOut controls SMM access-out policy

["Ni, Ray" <ray.ni@intel.com>]

This patch skips to update page table for non-SMRAM memory when
PcdCpuSmmAccessOut is TRUE.
So that when SMM accesses out, no page fault is triggered at all.

Signed-off-by: Ray Ni <ray.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
---
 UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c | 21 +++++++++++++++++----
 UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c    |  2 +-
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
index 69a04dfb23..427c33fb01 100644
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
@@ -130,6 +130,11 @@ UINT8                    mPhysicalAddressBits;
 UINT32                   mSmmCr0;
 UINT32                   mSmmCr4;
 
+//
+// Cache of PcdCpuSmmAccessOut
+//
+BOOLEAN                  mSmmAccessOut;
+
 /**
   Initialize IDT to setup exception handlers for SMM.
 
@@ -610,6 +615,12 @@ PiCpuSmmEntry (
   mSmmCodeAccessCheckEnable = PcdGetBool (PcdCpuSmmCodeAccessCheckEnable);
   DEBUG ((EFI_D_INFO, "PcdCpuSmmCodeAccessCheckEnable = %d\n", mSmmCodeAccessCheckEnable));
 
+  //
+  // Save the PcdCpuSmmAccessOut value into a global variable.
+  //
+  mSmmAccessOut = PcdGetBool (PcdCpuSmmAccessOut);
+  DEBUG ((DEBUG_INFO, "PcdCpuSmmAccessOut = %d\n", mSmmAccessOut));
+
   //
   // Save the PcdPteMemoryEncryptionAddressOrMask value into a global variable.
   // Make sure AddressEncMask is contained to smallest supported address field.
@@ -1431,10 +1442,12 @@ PerformRemainingTasks (
     //
     SetMemMapAttributes ();
 
-    //
-    // For outside SMRAM, we only map SMM communication buffer or MMIO.
-    //
-    SetUefiMemMapAttributes ();
+    if (!mSmmAccessOut) {
+      //
+      // For outside SMRAM, we only map SMM communication buffer or MMIO.
+      //
+      SetUefiMemMapAttributes ();
+    }
 
     //
     // Set page table itself to be read-only
diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
index a3b62f7787..6699aac65d 100644
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
@@ -1029,7 +1029,7 @@ SmiPFHandler (
       goto Exit;
     }
 
-    if (mCpuSmmStaticPageTable && IsSmmCommBufferForbiddenAddress (PFAddress)) {
+    if (IsSmmCommBufferForbiddenAddress (PFAddress)) {
       DumpCpuContext (InterruptType, SystemContext);
       DEBUG ((DEBUG_ERROR, "Access SMM communication forbidden address (0x%lx)!\n", PFAddress));
       DEBUG_CODE (
-- 
2.21.0.windows.1