[PATCH v8 14/32] OvmfPkg/MemEncryptSevLib: add support to validate system RAM

["Brijesh Singh" <brijesh.singh@amd.com>]

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275

Many of the integrity guarantees of SEV-SNP are enforced through the
Reverse Map Table (RMP). Each RMP entry contains the GPA at which a
particular page of DRAM should be mapped. The guest can request the
hypervisor to add pages in the RMP table via the Page State Change VMGEXIT
defined in the GHCB specification section 2.5.1 and 4.1.6. Inside each RMP
entry is a Validated flag; this flag is automatically cleared to 0 by the
CPU hardware when a new RMP entry is created for a guest. Each VM page
can be either validated or invalidated, as indicated by the Validated
flag in the RMP entry. Memory access to a private page that is not
validated generates a #VC. A VM can use the PVALIDATE instruction to
validate the private page before using it.

During the guest creation, the boot ROM memory is pre-validated by the
AMD-SEV firmware. The MemEncryptSevSnpValidateSystemRam() can be called
during the SEC and PEI phase to validate the detected system RAM.

One of the fields in the Page State Change NAE is the RMP page size. The
page size input parameter indicates that either a 4KB or 2MB page should
be used while adding the RMP entry. During the validation, when possible,
the MemEncryptSevSnpValidateSystemRam() will use the 2MB entry. A
hypervisor backing the memory may choose to use the different page size
in the RMP entry. In those cases, the PVALIDATE instruction should return
SIZEMISMATCH. If a SIZEMISMATCH is detected, then validate all 512-pages
constituting a 2MB region.

Upon completion, the PVALIDATE instruction sets the rFLAGS.CF to 0 if
instruction changed the RMP entry and to 1 if the instruction did not
change the RMP entry. The rFlags.CF will be 1 only when a memory region
is already validated. We should not double validate a memory
as it could lead to a security compromise. If double validation is
detected, terminate the boot.

Cc: Michael Roth <michael.roth@amd.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Jiewen Yao <Jiewen.yao@intel.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 OvmfPkg/OvmfPkgIa32.dsc                       |   1 +
 OvmfPkg/OvmfPkgIa32X64.dsc                    |   1 +
 .../DxeMemEncryptSevLib.inf                   |   3 +
 .../PeiMemEncryptSevLib.inf                   |   3 +
 .../SecMemEncryptSevLib.inf                   |   3 +
 OvmfPkg/Include/Library/MemEncryptSevLib.h    |  14 +
 .../X64/SnpPageStateChange.h                  |  31 ++
 .../Ia32/MemEncryptSevLib.c                   |  17 +
 .../X64/DxeSnpSystemRamValidate.c             |  40 +++
 .../X64/PeiSnpSystemRamValidate.c             |  36 +++
 .../X64/SecSnpSystemRamValidate.c             |  36 +++
 .../X64/SnpPageStateChangeInternal.c          | 295 ++++++++++++++++++
 12 files changed, 480 insertions(+)
 create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChange.h
 create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/DxeSnpSystemRamValidate.c
 create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c
 create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c
 create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c

diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
index d1d92c97bae3..626dbc15786a 100644
--- a/OvmfPkg/OvmfPkgIa32.dsc
+++ b/OvmfPkg/OvmfPkgIa32.dsc
@@ -266,6 +266,7 @@ [LibraryClasses.common.SEC]
 !else
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf
 !endif
+  MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
 
 [LibraryClasses.common.PEI_CORE]
   HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
index f42abc041c0c..58be97eb0605 100644
--- a/OvmfPkg/OvmfPkgIa32X64.dsc
+++ b/OvmfPkg/OvmfPkgIa32X64.dsc
@@ -270,6 +270,7 @@ [LibraryClasses.common.SEC]
 !else
   CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf
 !endif
+  MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
 
 [LibraryClasses.common.PEI_CORE]
   HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
index f2e162d68076..f613bb314f5f 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
@@ -34,8 +34,10 @@ [Sources]
   PeiDxeMemEncryptSevLibInternal.c
 
 [Sources.X64]
+  X64/DxeSnpSystemRamValidate.c
   X64/MemEncryptSevLib.c
   X64/PeiDxeVirtualMemory.c
+  X64/SnpPageStateChangeInternal.c
   X64/VirtualMemory.c
   X64/VirtualMemory.h
 
@@ -49,6 +51,7 @@ [LibraryClasses]
   DebugLib
   MemoryAllocationLib
   PcdLib
+  VmgExitLib
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
index 03a78c32df28..0402e49a1028 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
@@ -36,6 +36,8 @@ [Sources]
 [Sources.X64]
   X64/MemEncryptSevLib.c
   X64/PeiDxeVirtualMemory.c
+  X64/PeiSnpSystemRamValidate.c
+  X64/SnpPageStateChangeInternal.c
   X64/VirtualMemory.c
   X64/VirtualMemory.h
 
@@ -49,6 +51,7 @@ [LibraryClasses]
   DebugLib
   MemoryAllocationLib
   PcdLib
+  VmgExitLib
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
index 279c38bfbc2c..939af0a91ea4 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
@@ -35,6 +35,8 @@ [Sources]
 [Sources.X64]
   X64/MemEncryptSevLib.c
   X64/SecVirtualMemory.c
+  X64/SecSnpSystemRamValidate.c
+  X64/SnpPageStateChangeInternal.c
   X64/VirtualMemory.c
   X64/VirtualMemory.h
 
@@ -46,6 +48,7 @@ [LibraryClasses]
   CpuLib
   DebugLib
   PcdLib
+  VmgExitLib
 
 [FixedPcd]
   gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
diff --git a/OvmfPkg/Include/Library/MemEncryptSevLib.h b/OvmfPkg/Include/Library/MemEncryptSevLib.h
index 796de62ec2f8..f708a0cdaa72 100644
--- a/OvmfPkg/Include/Library/MemEncryptSevLib.h
+++ b/OvmfPkg/Include/Library/MemEncryptSevLib.h
@@ -215,4 +215,18 @@ MemEncryptSevClearMmioPageEncMask (
   IN UINTN                    NumPages
   );
 
+/**
+  Pre-validate the system RAM when SEV-SNP is enabled in the guest VM.
+
+  @param[in]  BaseAddress             Base address
+  @param[in]  NumPages                Number of pages starting from the base address
+
+**/
+VOID
+EFIAPI
+MemEncryptSevSnpPreValidateSystemRam (
+  IN PHYSICAL_ADDRESS           BaseAddress,
+  IN UINTN                      NumPages
+  );
+
 #endif // _MEM_ENCRYPT_SEV_LIB_H_
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChange.h b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChange.h
new file mode 100644
index 000000000000..8bbdf06468b9
--- /dev/null
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChange.h
@@ -0,0 +1,31 @@
+/** @file
+
+  SEV-SNP Page Validation functions.
+
+  Copyright (c) 2021 AMD Incorporated. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#ifndef SNP_PAGE_STATE_INTERNAL_H_
+#define SNP_PAGE_STATE_INTERNAL_H_
+
+//
+// SEV-SNP Page states
+//
+typedef enum {
+  SevSnpPagePrivate,
+  SevSnpPageShared,
+
+} SEV_SNP_PAGE_STATE;
+
+VOID
+InternalSetPageState (
+  IN EFI_PHYSICAL_ADDRESS             BaseAddress,
+  IN UINTN                            NumPages,
+  IN SEV_SNP_PAGE_STATE               State,
+  IN BOOLEAN                          UseLargeEntry
+  );
+
+#endif
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/Ia32/MemEncryptSevLib.c b/OvmfPkg/Library/BaseMemEncryptSevLib/Ia32/MemEncryptSevLib.c
index be260e0d1014..df5e4d61513d 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/Ia32/MemEncryptSevLib.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/Ia32/MemEncryptSevLib.c
@@ -136,3 +136,20 @@ MemEncryptSevClearMmioPageEncMask (
   //
   return RETURN_UNSUPPORTED;
 }
+
+/**
+  Pre-validate the system RAM when SEV-SNP is enabled in the guest VM.
+
+  @param[in]  BaseAddress             Base address
+  @param[in]  NumPages                Number of pages starting from the base address
+
+**/
+VOID
+EFIAPI
+MemEncryptSevSnpPreValidateSystemRam (
+  IN PHYSICAL_ADDRESS           BaseAddress,
+  IN UINTN                      NumPages
+  )
+{
+  ASSERT (FALSE);
+}
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/DxeSnpSystemRamValidate.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/DxeSnpSystemRamValidate.c
new file mode 100644
index 000000000000..ad8d8b388dc8
--- /dev/null
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/DxeSnpSystemRamValidate.c
@@ -0,0 +1,40 @@
+/** @file
+
+  SEV-SNP Page Validation functions.
+
+  Copyright (c) 2021 AMD Incorporated. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Uefi/UefiBaseType.h>
+#include <Library/BaseLib.h>
+#include <Library/DebugLib.h>
+#include <Library/MemEncryptSevLib.h>
+
+#include "SnpPageStateChange.h"
+
+/**
+  Pre-validate the system RAM when SEV-SNP is enabled in the guest VM.
+
+  @param[in]  BaseAddress             Base address
+  @param[in]  NumPages                Number of pages starting from the base address
+
+**/
+VOID
+EFIAPI
+MemEncryptSevSnpPreValidateSystemRam (
+  IN PHYSICAL_ADDRESS                   BaseAddress,
+  IN UINTN                              NumPages
+  )
+{
+  if (!MemEncryptSevSnpIsEnabled ()) {
+    return;
+  }
+
+  //
+  // All the pre-validation must be completed in the PEI phase.
+  //
+  ASSERT (FALSE);
+}
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c
new file mode 100644
index 000000000000..64aab7f45b6d
--- /dev/null
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c
@@ -0,0 +1,36 @@
+/** @file
+
+  SEV-SNP Page Validation functions.
+
+  Copyright (c) 2021 AMD Incorporated. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Uefi/UefiBaseType.h>
+#include <Library/BaseLib.h>
+#include <Library/MemEncryptSevLib.h>
+
+#include "SnpPageStateChange.h"
+
+/**
+  Pre-validate the system RAM when SEV-SNP is enabled in the guest VM.
+
+  @param[in]  BaseAddress             Base address
+  @param[in]  NumPages                Number of pages starting from the base address
+
+**/
+VOID
+EFIAPI
+MemEncryptSevSnpPreValidateSystemRam (
+  IN PHYSICAL_ADDRESS                   BaseAddress,
+  IN UINTN                              NumPages
+  )
+{
+  if (!MemEncryptSevSnpIsEnabled ()) {
+    return;
+  }
+
+  InternalSetPageState (BaseAddress, NumPages, SevSnpPagePrivate, TRUE);
+}
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c
new file mode 100644
index 000000000000..64aab7f45b6d
--- /dev/null
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c
@@ -0,0 +1,36 @@
+/** @file
+
+  SEV-SNP Page Validation functions.
+
+  Copyright (c) 2021 AMD Incorporated. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Uefi/UefiBaseType.h>
+#include <Library/BaseLib.h>
+#include <Library/MemEncryptSevLib.h>
+
+#include "SnpPageStateChange.h"
+
+/**
+  Pre-validate the system RAM when SEV-SNP is enabled in the guest VM.
+
+  @param[in]  BaseAddress             Base address
+  @param[in]  NumPages                Number of pages starting from the base address
+
+**/
+VOID
+EFIAPI
+MemEncryptSevSnpPreValidateSystemRam (
+  IN PHYSICAL_ADDRESS                   BaseAddress,
+  IN UINTN                              NumPages
+  )
+{
+  if (!MemEncryptSevSnpIsEnabled ()) {
+    return;
+  }
+
+  InternalSetPageState (BaseAddress, NumPages, SevSnpPagePrivate, TRUE);
+}
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
new file mode 100644
index 000000000000..506df12d4e51
--- /dev/null
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
@@ -0,0 +1,295 @@
+/** @file
+
+  SEV-SNP Page Validation functions.
+
+  Copyright (c) 2021 AMD Incorporated. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Uefi/UefiBaseType.h>
+#include <Library/BaseLib.h>
+#include <Library/BaseMemoryLib.h>
+#include <Library/MemEncryptSevLib.h>
+#include <Library/DebugLib.h>
+#include <Library/VmgExitLib.h>
+
+#include <Register/Amd/Ghcb.h>
+#include <Register/Amd/Msr.h>
+
+#include "SnpPageStateChange.h"
+
+#define IS_ALIGNED(x, y)        ((((x) & (y - 1)) == 0))
+#define PAGES_PER_LARGE_ENTRY   512
+
+STATIC
+UINTN
+MemoryStateToGhcbOp (
+  IN SEV_SNP_PAGE_STATE   State
+  )
+{
+  UINTN Cmd;
+
+  switch (State) {
+    case SevSnpPageShared: Cmd = SNP_PAGE_STATE_SHARED; break;
+    case SevSnpPagePrivate: Cmd = SNP_PAGE_STATE_PRIVATE; break;
+    default: ASSERT(0);
+  }
+
+  return Cmd;
+}
+
+STATIC
+VOID
+SnpPageStateFailureTerminate (
+  VOID
+  )
+{
+  MSR_SEV_ES_GHCB_REGISTER  Msr;
+
+  //
+  // Use the GHCB MSR Protocol to request termination by the hypervisor
+  //
+  Msr.GhcbPhysicalAddress = 0;
+  Msr.GhcbTerminate.Function = GHCB_INFO_TERMINATE_REQUEST;
+  Msr.GhcbTerminate.ReasonCodeSet = GHCB_TERMINATE_GHCB;
+  Msr.GhcbTerminate.ReasonCode = GHCB_TERMINATE_GHCB_GENERAL;
+  AsmWriteMsr64 (MSR_SEV_ES_GHCB, Msr.GhcbPhysicalAddress);
+
+  AsmVmgExit ();
+
+  ASSERT (FALSE);
+  CpuDeadLoop ();
+}
+
+/**
+ This function issues the PVALIDATE instruction to validate or invalidate the memory
+ range specified. If PVALIDATE returns size mismatch then it retry validating with
+ smaller page size.
+
+ */
+STATIC
+VOID
+PvalidateRange (
+  IN  SNP_PAGE_STATE_CHANGE_INFO    *Info,
+  IN  UINTN                         StartIndex,
+  IN  UINTN                         EndIndex,
+  IN  BOOLEAN                       Validate
+  )
+{
+  UINTN         Address, RmpPageSize, Ret, i;
+
+  for (; StartIndex <= EndIndex; StartIndex++) {
+    //
+    // Get the address and the page size from the Info.
+    //
+    Address = Info->Entry[StartIndex].GuestFrameNumber << EFI_PAGE_SHIFT;
+    RmpPageSize = Info->Entry[StartIndex].PageSize;
+
+    Ret = AsmPvalidate (RmpPageSize, Validate, Address);
+
+    //
+    // If we fail to validate due to size mismatch then try with the
+    // smaller page size. This senario will occur if the backing page in
+    // the RMP entry is 4K and we are validating it as a 2MB.
+    //
+    if ((Ret == PVALIDATE_RET_SIZE_MISMATCH) && (RmpPageSize == PvalidatePageSize2MB)) {
+      for (i = 0; i < PAGES_PER_LARGE_ENTRY; i++) {
+        Ret = AsmPvalidate (PvalidatePageSize4K, Validate, Address);
+        if (Ret) {
+          break;
+        }
+
+        Address = Address + EFI_PAGE_SIZE;
+      }
+    }
+
+    //
+    // If validation failed then do not continue.
+    //
+    if (Ret) {
+      DEBUG ((
+        DEBUG_ERROR, "%a:%a: Failed to %a address 0x%Lx Error code %d\n",
+        gEfiCallerBaseName,
+        __FUNCTION__,
+        Validate ? "Validate" : "Invalidate",
+        Address,
+        Ret
+        ));
+      SnpPageStateFailureTerminate ();
+    }
+  }
+}
+
+STATIC
+EFI_PHYSICAL_ADDRESS
+BuildPageStateBuffer (
+  IN EFI_PHYSICAL_ADDRESS           BaseAddress,
+  IN EFI_PHYSICAL_ADDRESS           EndAddress,
+  IN SEV_SNP_PAGE_STATE             State,
+  IN BOOLEAN                        UseLargeEntry,
+  IN SNP_PAGE_STATE_CHANGE_INFO     *Info
+  )
+{
+  EFI_PHYSICAL_ADDRESS      NextAddress;
+  UINTN                     i, RmpPageSize;
+
+  // Clear the page state structure
+  SetMem (Info, sizeof (*Info), 0);
+
+  i = 0;
+  NextAddress = EndAddress;
+
+  //
+  // Populate the page state entry structure
+  //
+  while ((BaseAddress < EndAddress) && (i < SNP_PAGE_STATE_MAX_ENTRY)) {
+    //
+    // Is this a 2MB aligned page? Check if we can use the Large RMP entry.
+    //
+    if (UseLargeEntry && IS_ALIGNED (BaseAddress, SIZE_2MB) &&
+      ((EndAddress - BaseAddress) >= SIZE_2MB)) {
+      RmpPageSize = PvalidatePageSize2MB;
+      NextAddress = BaseAddress + SIZE_2MB;
+    } else {
+      RmpPageSize = PvalidatePageSize4K;
+      NextAddress = BaseAddress + EFI_PAGE_SIZE;
+    }
+
+    Info->Entry[i].GuestFrameNumber = BaseAddress >> EFI_PAGE_SHIFT;
+    Info->Entry[i].PageSize = RmpPageSize;
+    Info->Entry[i].Operation = MemoryStateToGhcbOp (State);
+    Info->Entry[i].CurrentPage = 0;
+    Info->Header.EndEntry = i;
+
+    BaseAddress = NextAddress;
+    i++;
+  }
+
+  return NextAddress;
+}
+
+STATIC
+VOID
+PageStateChangeVmgExit (
+  IN GHCB                           *Ghcb,
+  IN SNP_PAGE_STATE_CHANGE_INFO     *Info
+  )
+{
+  EFI_STATUS                      Status;
+
+  //
+  // As per the GHCB specification, the hypervisor can resume the guest before
+  // processing all the entries. Checks whether all the entries are processed.
+  //
+  // The stragtegy here is to wait for the hypervisor to change the page
+  // state in the RMP table before guest access the memory pages. If the
+  // page state was not successful, then later memory access will result
+  // in the crash.
+  //
+  while (Info->Header.CurrentEntry <= Info->Header.EndEntry) {
+    Ghcb->SaveArea.SwScratch = (UINT64) Ghcb->SharedBuffer;
+    VmgSetOffsetValid (Ghcb, GhcbSwScratch);
+
+    Status = VmgExit (Ghcb, SVM_EXIT_SNP_PAGE_STATE_CHANGE, 0, 0);
+
+    //
+    // The Page State Change VMGEXIT can pass the failure through the
+    // ExitInfo2. Lets check both the return value as well as ExitInfo2.
+    //
+    if ((Status != 0) || (Ghcb->SaveArea.SwExitInfo2)) {
+      SnpPageStateFailureTerminate ();
+    }
+  }
+}
+
+/**
+ The function is used to set the page state when SEV-SNP is active. The page state
+ transition consist of changing the page ownership in the RMP table, and using the
+ PVALIDATE instruction to update the Validated bit in RMP table.
+
+ When the UseLargeEntry is set to TRUE, then function will try to use the large RMP
+ entry (whevever possible).
+ */
+VOID
+InternalSetPageState (
+  IN EFI_PHYSICAL_ADDRESS             BaseAddress,
+  IN UINTN                            NumPages,
+  IN SEV_SNP_PAGE_STATE               State,
+  IN BOOLEAN                          UseLargeEntry
+  )
+{
+  GHCB                            *Ghcb;
+  EFI_PHYSICAL_ADDRESS            NextAddress, EndAddress;
+  MSR_SEV_ES_GHCB_REGISTER        Msr;
+  BOOLEAN                         InterruptState;
+  SNP_PAGE_STATE_CHANGE_INFO      *Info;
+
+  Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
+  Ghcb = Msr.Ghcb;
+
+  EndAddress = BaseAddress + EFI_PAGES_TO_SIZE (NumPages);
+
+  DEBUG ((
+    DEBUG_VERBOSE, "%a:%a Address 0x%Lx - 0x%Lx State = %a LargeEntry = %d\n",
+    gEfiCallerBaseName,
+    __FUNCTION__,
+    BaseAddress,
+    EndAddress,
+    State == SevSnpPageShared ? "Shared" : "Private",
+    UseLargeEntry
+    ));
+
+  while (BaseAddress < EndAddress) {
+    UINTN       CurrentEntry, EndEntry;
+
+    //
+    // Initialize the GHCB
+    //
+    VmgInit (Ghcb, &InterruptState);
+
+    //
+    // Build the page state structure
+    //
+    Info = (SNP_PAGE_STATE_CHANGE_INFO *) Ghcb->SharedBuffer;
+    NextAddress = BuildPageStateBuffer (BaseAddress,
+                                        EndAddress,
+                                        State,
+                                        UseLargeEntry,
+                                        Info
+                                       );
+
+    //
+    // Save the current and end entry from the page state structure. We need
+    // it later.
+    //
+    CurrentEntry = Info->Header.CurrentEntry;
+    EndEntry = Info->Header.EndEntry;
+
+    //
+    // If the caller requested to change the page state to shared then
+    // invalidate the pages before making the page shared in the RMP table.
+    //
+    if (State == SevSnpPageShared) {
+      PvalidateRange (Info, CurrentEntry, EndEntry, FALSE);
+    }
+
+    //
+    // Invoke the page state change VMGEXIT.
+    //
+    PageStateChangeVmgExit (Ghcb, Info);
+
+    //
+    // If the caller requested to change the page state to private then
+    // validate the pages after it has been added in the RMP table.
+    //
+    if (State == SevSnpPagePrivate) {
+      PvalidateRange (Info, CurrentEntry, EndEntry, TRUE);
+    }
+
+    VmgDone (Ghcb, InterruptState);
+
+    BaseAddress = NextAddress;
+  }
+}
-- 
2.25.1