diff --git a/OvmfPkg/OvmfXen.dsc b/OvmfPkg/OvmfXen.dsc
index 1a0e59f0cc..7619a89382 100644
--- a/OvmfPkg/OvmfXen.dsc
+++ b/OvmfPkg/OvmfXen.dsc
@@ -523,7 +523,7 @@ [Components]
   }
   MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
 
-  OvmfPkg/PlatformPei/PlatformPei.inf
+  OvmfPkg/XenPlatformPei/XenPlatformPei.inf
   UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume2Pei.inf
   UefiCpuPkg/CpuMpPei/CpuMpPei.inf
 
diff --git a/OvmfPkg/OvmfXen.fdf b/OvmfPkg/OvmfXen.fdf
index 6fc8479aae..2ceff7baa2 100644
--- a/OvmfPkg/OvmfXen.fdf
+++ b/OvmfPkg/OvmfXen.fdf
@@ -152,7 +152,7 @@ [FV.PEIFV]
 INF  MdeModulePkg/Universal/PCD/Pei/Pcd.inf
 INF  MdeModulePkg/Universal/ReportStatusCodeRouter/Pei/ReportStatusCodeRouterPei.inf
 INF  MdeModulePkg/Universal/StatusCodeHandler/Pei/StatusCodeHandlerPei.inf
-INF  OvmfPkg/PlatformPei/PlatformPei.inf
+INF  OvmfPkg/XenPlatformPei/XenPlatformPei.inf
 INF  MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
 INF  UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume2Pei.inf
 INF  UefiCpuPkg/CpuMpPei/CpuMpPei.inf
diff --git a/OvmfPkg/XenPlatformPei/XenPlatformPei.inf b/OvmfPkg/XenPlatformPei/XenPlatformPei.inf
new file mode 100644
index 0000000000..d1265c365a
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/XenPlatformPei.inf
@@ -0,0 +1,96 @@
+## @file
+#  Platform PEI driver
+#
+#  This module provides platform specific function to detect boot mode.
+#  Copyright (c) 2006 - 2019, Intel Corporation. All rights reserved.<BR>
+#  Copyright (c) 2019, Citrix Systems, Inc.
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = XenPlatformPei
+  FILE_GUID                      = f112a6ee-993a-4f0b-8295-e52029d9b4ba
+  MODULE_TYPE                    = PEIM
+  VERSION_STRING                 = 1.0
+  ENTRY_POINT                    = InitializeXenPlatform
+
+#
+# The following information is for reference only and not required by the build tools.
+#
+#  VALID_ARCHITECTURES           = IA32 X64 EBC
+#
+
+[Sources]
+  AmdSev.c
+  ClearCache.c
+  Cmos.c
+  Cmos.h
+  Fv.c
+  MemDetect.c
+  Platform.c
+  Platform.h
+  Xen.c
+  Xen.h
+
+[Packages]
+  MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
+  SecurityPkg/SecurityPkg.dec
+  UefiCpuPkg/UefiCpuPkg.dec
+  OvmfPkg/OvmfPkg.dec
+
+[Guids]
+  gEfiMemoryTypeInformationGuid
+  gEfiXenInfoGuid
+
+[LibraryClasses]
+  BaseLib
+  CacheMaintenanceLib
+  DebugLib
+  HobLib
+  IoLib
+  PciLib
+  ResourcePublicationLib
+  PeiServicesLib
+  PeimEntryPoint
+  MtrrLib
+  MemEncryptSevLib
+  PcdLib
+
+[Pcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfLockBoxStorageBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfLockBoxStorageSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfHostBridgePciDevId
+  gUefiOvmfPkgTokenSpaceGuid.PcdPciIoBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdPciIoSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdPciMmio32Base
+  gUefiOvmfPkgTokenSpaceGuid.PcdPciMmio32Size
+  gUefiOvmfPkgTokenSpaceGuid.PcdPciMmio64Base
+  gUefiOvmfPkgTokenSpaceGuid.PcdPciMmio64Size
+  gUefiOvmfPkgTokenSpaceGuid.PcdQ35TsegMbytes
+  gEfiMdeModulePkgTokenSpaceGuid.PcdFlashNvStorageFtwSpareSize
+  gEfiMdeModulePkgTokenSpaceGuid.PcdEmuVariableNvStoreReserved
+  gEfiMdeModulePkgTokenSpaceGuid.PcdPciDisableBusEnumeration
+  gEfiMdeModulePkgTokenSpaceGuid.PcdDxeIplSwitchToLongMode
+  gEfiMdeModulePkgTokenSpaceGuid.PcdUse1GPageTable
+  gEfiMdeModulePkgTokenSpaceGuid.PcdPteMemoryEncryptionAddressOrMask
+  gEfiSecurityPkgTokenSpaceGuid.PcdOptionRomImageVerificationPolicy
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuLocalApicBaseAddress
+
+[FixedPcd]
+  gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
+
+[Ppis]
+  gEfiPeiMasterBootModePpiGuid
+  gEfiPeiMpServicesPpiGuid
+
+[Depex]
+  TRUE
+
diff --git a/OvmfPkg/XenPlatformPei/Cmos.h b/OvmfPkg/XenPlatformPei/Cmos.h
new file mode 100644
index 0000000000..80ffcb002f
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/Cmos.h
@@ -0,0 +1,52 @@
+/** @file
+  PC/AT CMOS access routines
+
+  Copyright (c) 2006 - 2009, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2019, Citrix Systems, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#ifndef __CMOS_H__
+#define __CMOS_H__
+
+/**
+  Reads 8-bits of CMOS data.
+
+  Reads the 8-bits of CMOS data at the location specified by Index.
+  The 8-bit read value is returned.
+
+  @param  Index  The CMOS location to read.
+
+  @return The value read.
+
+**/
+UINT8
+EFIAPI
+CmosRead8 (
+  IN      UINTN                     Index
+  );
+
+/**
+  Writes 8-bits of CMOS data.
+
+  Writes 8-bits of CMOS data to the location specified by Index
+  with the value specified by Value and returns Value.
+
+  @param  Index  The CMOS location to write.
+  @param  Value  The value to write to CMOS.
+
+  @return The value written to CMOS.
+
+**/
+UINT8
+EFIAPI
+CmosWrite8 (
+  IN      UINTN                     Index,
+  IN      UINT8                     Value
+  );
+
+
+#endif
+
diff --git a/OvmfPkg/XenPlatformPei/Platform.h b/OvmfPkg/XenPlatformPei/Platform.h
new file mode 100644
index 0000000000..77427496c0
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/Platform.h
@@ -0,0 +1,108 @@
+/** @file
+  Platform PEI module include file.
+
+  Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2019, Citrix Systems, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#ifndef _PLATFORM_PEI_H_INCLUDED_
+#define _PLATFORM_PEI_H_INCLUDED_
+
+#include <IndustryStandard/E820.h>
+
+VOID
+AddIoMemoryBaseSizeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  UINT64                      MemorySize
+  );
+
+VOID
+AddIoMemoryRangeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  EFI_PHYSICAL_ADDRESS        MemoryLimit
+  );
+
+VOID
+AddMemoryBaseSizeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  UINT64                      MemorySize
+  );
+
+VOID
+AddMemoryRangeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  EFI_PHYSICAL_ADDRESS        MemoryLimit
+  );
+
+VOID
+AddReservedMemoryBaseSizeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  UINT64                      MemorySize,
+  BOOLEAN                     Cacheable
+  );
+
+VOID
+AddressWidthInitialization (
+  VOID
+  );
+
+VOID
+Q35TsegMbytesInitialization (
+  VOID
+  );
+
+EFI_STATUS
+PublishPeiMemory (
+  VOID
+  );
+
+UINT32
+GetSystemMemorySizeBelow4gb (
+  VOID
+  );
+
+VOID
+InitializeRamRegions (
+  VOID
+  );
+
+EFI_STATUS
+PeiFvInitialization (
+  VOID
+  );
+
+VOID
+InstallClearCacheCallback (
+  VOID
+  );
+
+EFI_STATUS
+InitializeXen (
+  VOID
+  );
+
+BOOLEAN
+XenDetect (
+  VOID
+  );
+
+VOID
+AmdSevInitialize (
+  VOID
+  );
+
+VOID
+XenPublishRamRegions (
+  VOID
+  );
+
+extern EFI_BOOT_MODE mBootMode;
+
+extern UINT8 mPhysMemAddressWidth;
+
+extern UINT16 mHostBridgeDevId;
+
+#endif // _PLATFORM_PEI_H_INCLUDED_
diff --git a/OvmfPkg/XenPlatformPei/Xen.h b/OvmfPkg/XenPlatformPei/Xen.h
new file mode 100644
index 0000000000..2605481280
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/Xen.h
@@ -0,0 +1,39 @@
+/** @file
+  Ovmf info structure passed by Xen
+
+Copyright (c) 2013, Citrix Systems UK Ltd.<BR>
+
+SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#ifndef __XEN_H__
+#define __XEN_H__
+
+#include <PiPei.h>
+
+// Physical address of OVMF info
+#define OVMF_INFO_PHYSICAL_ADDRESS 0x00001000
+
+// This structure must match the definition on Xen side
+#pragma pack(1)
+typedef struct {
+  CHAR8 Signature[14]; // XenHVMOVMF\0
+  UINT8 Length;        // Length of this structure
+  UINT8 Checksum;      // Set such that the sum over bytes 0..length == 0
+  //
+  // Physical address of an array of TablesCount elements.
+  //
+  // Each element contains the physical address of a BIOS table.
+  //
+  EFI_PHYSICAL_ADDRESS Tables;
+  UINT32 TablesCount;
+  //
+  // Physical address of the E820 table, contains E820EntriesCount entries.
+  //
+  EFI_PHYSICAL_ADDRESS E820;
+  UINT32 E820EntriesCount;
+} EFI_XEN_OVMF_INFO;
+#pragma pack()
+
+#endif /* __XEN_H__ */
diff --git a/OvmfPkg/XenPlatformPei/AmdSev.c b/OvmfPkg/XenPlatformPei/AmdSev.c
new file mode 100644
index 0000000000..7ebbb5cc1f
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/AmdSev.c
@@ -0,0 +1,64 @@
+/**@file
+  Initialize Secure Encrypted Virtualization (SEV) support
+
+  Copyright (c) 2017, Advanced Micro Devices. All rights reserved.<BR>
+  Copyright (c) 2019, Citrix Systems, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+//
+// The package level header files this module uses
+//
+#include <Library/DebugLib.h>
+#include <Library/MemEncryptSevLib.h>
+#include <Library/PcdLib.h>
+#include <PiPei.h>
+#include <Register/Amd/Cpuid.h>
+#include <Register/Cpuid.h>
+
+#include "Platform.h"
+
+/**
+
+  Function checks if SEV support is available, if present then it sets
+  the dynamic PcdPteMemoryEncryptionAddressOrMask with memory encryption mask.
+
+  **/
+VOID
+AmdSevInitialize (
+  VOID
+  )
+{
+  CPUID_MEMORY_ENCRYPTION_INFO_EBX  Ebx;
+  UINT64                            EncryptionMask;
+  RETURN_STATUS                     PcdStatus;
+
+  //
+  // Check if SEV is enabled
+  //
+  if (!MemEncryptSevIsEnabled ()) {
+    return;
+  }
+
+  //
+  // CPUID Fn8000_001F[EBX] Bit 0:5 (memory encryption bit position)
+  //
+  AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, NULL, &Ebx.Uint32, NULL, NULL);
+  EncryptionMask = LShiftU64 (1, Ebx.Bits.PtePosBits);
+
+  //
+  // Set Memory Encryption Mask PCD
+  //
+  PcdStatus = PcdSet64S (PcdPteMemoryEncryptionAddressOrMask, EncryptionMask);
+  ASSERT_RETURN_ERROR (PcdStatus);
+
+  DEBUG ((DEBUG_INFO, "SEV is enabled (mask 0x%lx)\n", EncryptionMask));
+
+  //
+  // Set Pcd to Deny the execution of option ROM when security
+  // violation.
+  //
+  PcdStatus = PcdSet32S (PcdOptionRomImageVerificationPolicy, 0x4);
+  ASSERT_RETURN_ERROR (PcdStatus);
+}
diff --git a/OvmfPkg/XenPlatformPei/ClearCache.c b/OvmfPkg/XenPlatformPei/ClearCache.c
new file mode 100644
index 0000000000..fab53633a9
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/ClearCache.c
@@ -0,0 +1,112 @@
+/**@file
+  Install a callback to clear cache on all processors.
+  This is for conformance with the TCG "Platform Reset Attack Mitigation
+  Specification". Because clearing the CPU caches at boot doesn't impact
+  performance significantly, do it unconditionally, for simplicity's
+  sake.
+
+  Copyright (C) 2018, Red Hat, Inc.
+  Copyright (c) 2019, Citrix Systems, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#include <Library/CacheMaintenanceLib.h>
+#include <Library/DebugLib.h>
+#include <Library/PeiServicesLib.h>
+#include <Ppi/MpServices.h>
+
+#include "Platform.h"
+
+/**
+  Invalidate data & instruction caches.
+  All APs execute this function in parallel. The BSP executes the function
+  separately.
+
+  @param[in,out] WorkSpace  Pointer to the input/output argument workspace
+                            shared by all processors.
+**/
+STATIC
+VOID
+EFIAPI
+ClearCache (
+  IN OUT VOID *WorkSpace
+  )
+{
+  WriteBackInvalidateDataCache ();
+  InvalidateInstructionCache ();
+}
+
+/**
+  Notification function called when EFI_PEI_MP_SERVICES_PPI becomes available.
+
+  @param[in] PeiServices      Indirect reference to the PEI Services Table.
+  @param[in] NotifyDescriptor Address of the notification descriptor data
+                              structure.
+  @param[in] Ppi              Address of the PPI that was installed.
+
+  @return  Status of the notification. The status code returned from this
+           function is ignored.
+**/
+STATIC
+EFI_STATUS
+EFIAPI
+ClearCacheOnMpServicesAvailable (
+  IN EFI_PEI_SERVICES           **PeiServices,
+  IN EFI_PEI_NOTIFY_DESCRIPTOR  *NotifyDescriptor,
+  IN VOID                       *Ppi
+  )
+{
+  EFI_PEI_MP_SERVICES_PPI *MpServices;
+  EFI_STATUS              Status;
+
+  DEBUG ((DEBUG_INFO, "%a: %a\n", gEfiCallerBaseName, __FUNCTION__));
+
+  //
+  // Clear cache on all the APs in parallel.
+  //
+  MpServices = Ppi;
+  Status = MpServices->StartupAllAPs (
+                         (CONST EFI_PEI_SERVICES **)PeiServices,
+                         MpServices,
+                         ClearCache,          // Procedure
+                         FALSE,               // SingleThread
+                         0,                   // TimeoutInMicroSeconds: inf.
+                         NULL                 // ProcedureArgument
+                         );
+  if (EFI_ERROR (Status) && Status != EFI_NOT_STARTED) {
+    DEBUG ((DEBUG_ERROR, "%a: StartupAllAps(): %r\n", __FUNCTION__, Status));
+    return Status;
+  }
+
+  //
+  // Now clear cache on the BSP too.
+  //
+  ClearCache (NULL);
+  return EFI_SUCCESS;
+}
+
+//
+// Notification object for registering the callback, for when
+// EFI_PEI_MP_SERVICES_PPI becomes available.
+//
+STATIC CONST EFI_PEI_NOTIFY_DESCRIPTOR mMpServicesNotify = {
+  EFI_PEI_PPI_DESCRIPTOR_NOTIFY_CALLBACK | // Flags
+  EFI_PEI_PPI_DESCRIPTOR_TERMINATE_LIST,
+  &gEfiPeiMpServicesPpiGuid,               // Guid
+  ClearCacheOnMpServicesAvailable          // Notify
+};
+
+VOID
+InstallClearCacheCallback (
+  VOID
+  )
+{
+  EFI_STATUS           Status;
+
+  Status = PeiServicesNotifyPpi (&mMpServicesNotify);
+  if (EFI_ERROR (Status)) {
+    DEBUG ((DEBUG_ERROR, "%a: failed to set up MP Services callback: %r\n",
+      __FUNCTION__, Status));
+  }
+}
diff --git a/OvmfPkg/XenPlatformPei/Cmos.c b/OvmfPkg/XenPlatformPei/Cmos.c
new file mode 100644
index 0000000000..5d9ee67cd8
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/Cmos.c
@@ -0,0 +1,60 @@
+/** @file
+  PC/AT CMOS access routines
+
+  Copyright (c) 2006 - 2009, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2019, Citrix Systems, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+
+#include "Cmos.h"
+#include "Library/IoLib.h"
+
+/**
+  Reads 8-bits of CMOS data.
+
+  Reads the 8-bits of CMOS data at the location specified by Index.
+  The 8-bit read value is returned.
+
+  @param  Index  The CMOS location to read.
+
+  @return The value read.
+
+**/
+UINT8
+EFIAPI
+CmosRead8 (
+  IN      UINTN                     Index
+  )
+{
+  IoWrite8 (0x70, (UINT8) Index);
+  return IoRead8 (0x71);
+}
+
+
+/**
+  Writes 8-bits of CMOS data.
+
+  Writes 8-bits of CMOS data to the location specified by Index
+  with the value specified by Value and returns Value.
+
+  @param  Index  The CMOS location to write.
+  @param  Value  The value to write to CMOS.
+
+  @return The value written to CMOS.
+
+**/
+UINT8
+EFIAPI
+CmosWrite8 (
+  IN      UINTN                     Index,
+  IN      UINT8                     Value
+  )
+{
+  IoWrite8 (0x70, (UINT8) Index);
+  IoWrite8 (0x71, Value);
+  return Value;
+}
+
diff --git a/OvmfPkg/XenPlatformPei/Fv.c b/OvmfPkg/XenPlatformPei/Fv.c
new file mode 100644
index 0000000000..70e9b52700
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/Fv.c
@@ -0,0 +1,76 @@
+/** @file
+  Build FV related hobs for platform.
+
+  Copyright (c) 2006 - 2013, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2019, Citrix Systems, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include "PiPei.h"
+#include "Platform.h"
+#include <Library/DebugLib.h>
+#include <Library/HobLib.h>
+#include <Library/PeiServicesLib.h>
+#include <Library/PcdLib.h>
+
+
+/**
+  Publish PEI & DXE (Decompressed) Memory based FVs to let PEI
+  and DXE know about them.
+
+  @retval EFI_SUCCESS   Platform PEI FVs were initialized successfully.
+
+**/
+EFI_STATUS
+PeiFvInitialization (
+  VOID
+  )
+{
+  DEBUG ((DEBUG_INFO, "Platform PEI Firmware Volume Initialization\n"));
+
+  //
+  // Create a memory allocation HOB for the PEI FV.
+  //
+  // Allocate as ACPI NVS is S3 is supported
+  //
+  BuildMemoryAllocationHob (
+    PcdGet32 (PcdOvmfPeiMemFvBase),
+    PcdGet32 (PcdOvmfPeiMemFvSize),
+    EfiBootServicesData
+    );
+
+  //
+  // Let DXE know about the DXE FV
+  //
+  BuildFvHob (PcdGet32 (PcdOvmfDxeMemFvBase), PcdGet32 (PcdOvmfDxeMemFvSize));
+
+  //
+  // Create a memory allocation HOB for the DXE FV.
+  //
+  // If "secure" S3 is needed, then SEC will decompress both PEI and DXE
+  // firmware volumes at S3 resume too, hence we need to keep away the OS from
+  // DXEFV as well. Otherwise we only need to keep away DXE itself from the
+  // DXEFV area.
+  //
+  BuildMemoryAllocationHob (
+    PcdGet32 (PcdOvmfDxeMemFvBase),
+    PcdGet32 (PcdOvmfDxeMemFvSize),
+    EfiBootServicesData
+    );
+
+  //
+  // Let PEI know about the DXE FV so it can find the DXE Core
+  //
+  PeiServicesInstallFvInfoPpi (
+    NULL,
+    (VOID *)(UINTN) PcdGet32 (PcdOvmfDxeMemFvBase),
+    PcdGet32 (PcdOvmfDxeMemFvSize),
+    NULL,
+    NULL
+    );
+
+  return EFI_SUCCESS;
+}
+
diff --git a/OvmfPkg/XenPlatformPei/MemDetect.c b/OvmfPkg/XenPlatformPei/MemDetect.c
new file mode 100644
index 0000000000..cf95f9c474
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/MemDetect.c
@@ -0,0 +1,421 @@
+/**@file
+  Memory Detection for Virtual Machines.
+
+  Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2019, Citrix Systems, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+Module Name:
+
+  MemDetect.c
+
+**/
+
+//
+// The package level header files this module uses
+//
+#include <IndustryStandard/Q35MchIch9.h>
+#include <PiPei.h>
+
+//
+// The Library classes this module consumes
+//
+#include <Library/BaseLib.h>
+#include <Library/BaseMemoryLib.h>
+#include <Library/DebugLib.h>
+#include <Library/HobLib.h>
+#include <Library/IoLib.h>
+#include <Library/PcdLib.h>
+#include <Library/PciLib.h>
+#include <Library/PeimEntryPoint.h>
+#include <Library/ResourcePublicationLib.h>
+
+#include "Platform.h"
+#include "Cmos.h"
+
+UINT8 mPhysMemAddressWidth;
+
+STATIC UINT32 mS3AcpiReservedMemoryBase;
+STATIC UINT32 mS3AcpiReservedMemorySize;
+
+STATIC UINT16 mQ35TsegMbytes;
+
+VOID
+Q35TsegMbytesInitialization (
+  VOID
+  )
+{
+  UINT16        ExtendedTsegMbytes;
+  RETURN_STATUS PcdStatus;
+
+  if (mHostBridgeDevId != INTEL_Q35_MCH_DEVICE_ID) {
+    DEBUG ((
+      DEBUG_ERROR,
+      "%a: no TSEG (SMRAM) on host bridge DID=0x%04x; "
+      "only DID=0x%04x (Q35) is supported\n",
+      __FUNCTION__,
+      mHostBridgeDevId,
+      INTEL_Q35_MCH_DEVICE_ID
+      ));
+    ASSERT (FALSE);
+    CpuDeadLoop ();
+  }
+
+  //
+  // Check if QEMU offers an extended TSEG.
+  //
+  // This can be seen from writing MCH_EXT_TSEG_MB_QUERY to the MCH_EXT_TSEG_MB
+  // register, and reading back the register.
+  //
+  // On a QEMU machine type that does not offer an extended TSEG, the initial
+  // write overwrites whatever value a malicious guest OS may have placed in
+  // the (unimplemented) register, before entering S3 or rebooting.
+  // Subsequently, the read returns MCH_EXT_TSEG_MB_QUERY unchanged.
+  //
+  // On a QEMU machine type that offers an extended TSEG, the initial write
+  // triggers an update to the register. Subsequently, the value read back
+  // (which is guaranteed to differ from MCH_EXT_TSEG_MB_QUERY) tells us the
+  // number of megabytes.
+  //
+  PciWrite16 (DRAMC_REGISTER_Q35 (MCH_EXT_TSEG_MB), MCH_EXT_TSEG_MB_QUERY);
+  ExtendedTsegMbytes = PciRead16 (DRAMC_REGISTER_Q35 (MCH_EXT_TSEG_MB));
+  if (ExtendedTsegMbytes == MCH_EXT_TSEG_MB_QUERY) {
+    mQ35TsegMbytes = PcdGet16 (PcdQ35TsegMbytes);
+    return;
+  }
+
+  DEBUG ((
+    DEBUG_INFO,
+    "%a: QEMU offers an extended TSEG (%d MB)\n",
+    __FUNCTION__,
+    ExtendedTsegMbytes
+    ));
+  PcdStatus = PcdSet16S (PcdQ35TsegMbytes, ExtendedTsegMbytes);
+  ASSERT_RETURN_ERROR (PcdStatus);
+  mQ35TsegMbytes = ExtendedTsegMbytes;
+}
+
+
+UINT32
+GetSystemMemorySizeBelow4gb (
+  VOID
+  )
+{
+  UINT8 Cmos0x34;
+  UINT8 Cmos0x35;
+
+  //
+  // CMOS 0x34/0x35 specifies the system memory above 16 MB.
+  // * CMOS(0x35) is the high byte
+  // * CMOS(0x34) is the low byte
+  // * The size is specified in 64kb chunks
+  // * Since this is memory above 16MB, the 16MB must be added
+  //   into the calculation to get the total memory size.
+  //
+
+  Cmos0x34 = (UINT8) CmosRead8 (0x34);
+  Cmos0x35 = (UINT8) CmosRead8 (0x35);
+
+  return (UINT32) (((UINTN)((Cmos0x35 << 8) + Cmos0x34) << 16) + SIZE_16MB);
+}
+
+
+STATIC
+UINT64
+GetSystemMemorySizeAbove4gb (
+  )
+{
+  UINT32 Size;
+  UINTN  CmosIndex;
+
+  //
+  // CMOS 0x5b-0x5d specifies the system memory above 4GB MB.
+  // * CMOS(0x5d) is the most significant size byte
+  // * CMOS(0x5c) is the middle size byte
+  // * CMOS(0x5b) is the least significant size byte
+  // * The size is specified in 64kb chunks
+  //
+
+  Size = 0;
+  for (CmosIndex = 0x5d; CmosIndex >= 0x5b; CmosIndex--) {
+    Size = (UINT32) (Size << 8) + (UINT32) CmosRead8 (CmosIndex);
+  }
+
+  return LShiftU64 (Size, 16);
+}
+
+
+/**
+  Return the highest address that DXE could possibly use, plus one.
+**/
+STATIC
+UINT64
+GetFirstNonAddress (
+  VOID
+  )
+{
+  UINT64               FirstNonAddress;
+  UINT64               Pci64Base, Pci64Size;
+  RETURN_STATUS        PcdStatus;
+
+  FirstNonAddress = BASE_4GB + GetSystemMemorySizeAbove4gb ();
+
+  //
+  // If DXE is 32-bit, then we're done; PciBusDxe will degrade 64-bit MMIO
+  // resources to 32-bit anyway. See DegradeResource() in
+  // "PciResourceSupport.c".
+  //
+#ifdef MDE_CPU_IA32
+  if (!FeaturePcdGet (PcdDxeIplSwitchToLongMode)) {
+    return FirstNonAddress;
+  }
+#endif
+
+  //
+  // Otherwise, in order to calculate the highest address plus one, we must
+  // consider the 64-bit PCI host aperture too. Fetch the default size.
+  //
+  Pci64Size = PcdGet64 (PcdPciMmio64Size);
+
+  if (Pci64Size == 0) {
+    if (mBootMode != BOOT_ON_S3_RESUME) {
+      DEBUG ((DEBUG_INFO, "%a: disabling 64-bit PCI host aperture\n",
+        __FUNCTION__));
+      PcdStatus = PcdSet64S (PcdPciMmio64Size, 0);
+      ASSERT_RETURN_ERROR (PcdStatus);
+    }
+
+    //
+    // There's nothing more to do; the amount of memory above 4GB fully
+    // determines the highest address plus one. The memory hotplug area (see
+    // below) plays no role for the firmware in this case.
+    //
+    return FirstNonAddress;
+  }
+
+  //
+  // SeaBIOS aligns both boundaries of the 64-bit PCI host aperture to 1GB, so
+  // that the host can map it with 1GB hugepages. Follow suit.
+  //
+  Pci64Base = ALIGN_VALUE (FirstNonAddress, (UINT64)SIZE_1GB);
+  Pci64Size = ALIGN_VALUE (Pci64Size, (UINT64)SIZE_1GB);
+
+  //
+  // The 64-bit PCI host aperture should also be "naturally" aligned. The
+  // alignment is determined by rounding the size of the aperture down to the
+  // next smaller or equal power of two. That is, align the aperture by the
+  // largest BAR size that can fit into it.
+  //
+  Pci64Base = ALIGN_VALUE (Pci64Base, GetPowerOfTwo64 (Pci64Size));
+
+  if (mBootMode != BOOT_ON_S3_RESUME) {
+    //
+    // The core PciHostBridgeDxe driver will automatically add this range to
+    // the GCD memory space map through our PciHostBridgeLib instance; here we
+    // only need to set the PCDs.
+    //
+    PcdStatus = PcdSet64S (PcdPciMmio64Base, Pci64Base);
+    ASSERT_RETURN_ERROR (PcdStatus);
+    PcdStatus = PcdSet64S (PcdPciMmio64Size, Pci64Size);
+    ASSERT_RETURN_ERROR (PcdStatus);
+
+    DEBUG ((DEBUG_INFO, "%a: Pci64Base=0x%Lx Pci64Size=0x%Lx\n",
+      __FUNCTION__, Pci64Base, Pci64Size));
+  }
+
+  //
+  // The useful address space ends with the 64-bit PCI host aperture.
+  //
+  FirstNonAddress = Pci64Base + Pci64Size;
+  return FirstNonAddress;
+}
+
+
+/**
+  Initialize the mPhysMemAddressWidth variable, based on guest RAM size.
+**/
+VOID
+AddressWidthInitialization (
+  VOID
+  )
+{
+  UINT64 FirstNonAddress;
+
+  //
+  // As guest-physical memory size grows, the permanent PEI RAM requirements
+  // are dominated by the identity-mapping page tables built by the DXE IPL.
+  // The DXL IPL keys off of the physical address bits advertized in the CPU
+  // HOB. To conserve memory, we calculate the minimum address width here.
+  //
+  FirstNonAddress      = GetFirstNonAddress ();
+  mPhysMemAddressWidth = (UINT8)HighBitSet64 (FirstNonAddress);
+
+  //
+  // If FirstNonAddress is not an integral power of two, then we need an
+  // additional bit.
+  //
+  if ((FirstNonAddress & (FirstNonAddress - 1)) != 0) {
+    ++mPhysMemAddressWidth;
+  }
+
+  //
+  // The minimum address width is 36 (covers up to and excluding 64 GB, which
+  // is the maximum for Ia32 + PAE). The theoretical architecture maximum for
+  // X64 long mode is 52 bits, but the DXE IPL clamps that down to 48 bits. We
+  // can simply assert that here, since 48 bits are good enough for 256 TB.
+  //
+  if (mPhysMemAddressWidth <= 36) {
+    mPhysMemAddressWidth = 36;
+  }
+  ASSERT (mPhysMemAddressWidth <= 48);
+}
+
+
+/**
+  Calculate the cap for the permanent PEI memory.
+**/
+STATIC
+UINT32
+GetPeiMemoryCap (
+  VOID
+  )
+{
+  BOOLEAN Page1GSupport;
+  UINT32  RegEax;
+  UINT32  RegEdx;
+  UINT32  Pml4Entries;
+  UINT32  PdpEntries;
+  UINTN   TotalPages;
+
+  //
+  // If DXE is 32-bit, then just return the traditional 64 MB cap.
+  //
+#ifdef MDE_CPU_IA32
+  if (!FeaturePcdGet (PcdDxeIplSwitchToLongMode)) {
+    return SIZE_64MB;
+  }
+#endif
+
+  //
+  // Dependent on physical address width, PEI memory allocations can be
+  // dominated by the page tables built for 64-bit DXE. So we key the cap off
+  // of those. The code below is based on CreateIdentityMappingPageTables() in
+  // "MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c".
+  //
+  Page1GSupport = FALSE;
+  if (PcdGetBool (PcdUse1GPageTable)) {
+    AsmCpuid (0x80000000, &RegEax, NULL, NULL, NULL);
+    if (RegEax >= 0x80000001) {
+      AsmCpuid (0x80000001, NULL, NULL, NULL, &RegEdx);
+      if ((RegEdx & BIT26) != 0) {
+        Page1GSupport = TRUE;
+      }
+    }
+  }
+
+  if (mPhysMemAddressWidth <= 39) {
+    Pml4Entries = 1;
+    PdpEntries = 1 << (mPhysMemAddressWidth - 30);
+    ASSERT (PdpEntries <= 0x200);
+  } else {
+    Pml4Entries = 1 << (mPhysMemAddressWidth - 39);
+    ASSERT (Pml4Entries <= 0x200);
+    PdpEntries = 512;
+  }
+
+  TotalPages = Page1GSupport ? Pml4Entries + 1 :
+                               (PdpEntries + 1) * Pml4Entries + 1;
+  ASSERT (TotalPages <= 0x40201);
+
+  //
+  // Add 64 MB for miscellaneous allocations. Note that for
+  // mPhysMemAddressWidth values close to 36, the cap will actually be
+  // dominated by this increment.
+  //
+  return (UINT32)(EFI_PAGES_TO_SIZE (TotalPages) + SIZE_64MB);
+}
+
+
+/**
+  Publish PEI core memory
+
+  @return EFI_SUCCESS     The PEIM initialized successfully.
+
+**/
+EFI_STATUS
+PublishPeiMemory (
+  VOID
+  )
+{
+  EFI_STATUS                  Status;
+  EFI_PHYSICAL_ADDRESS        MemoryBase;
+  UINT64                      MemorySize;
+  UINT32                      LowerMemorySize;
+  UINT32                      PeiMemoryCap;
+
+  LowerMemorySize = GetSystemMemorySizeBelow4gb ();
+
+  if (mBootMode == BOOT_ON_S3_RESUME) {
+    MemoryBase = mS3AcpiReservedMemoryBase;
+    MemorySize = mS3AcpiReservedMemorySize;
+  } else {
+    PeiMemoryCap = GetPeiMemoryCap ();
+    DEBUG ((DEBUG_INFO, "%a: mPhysMemAddressWidth=%d PeiMemoryCap=%u KB\n",
+      __FUNCTION__, mPhysMemAddressWidth, PeiMemoryCap >> 10));
+
+    //
+    // Determine the range of memory to use during PEI
+    //
+    MemoryBase =
+      PcdGet32 (PcdOvmfDxeMemFvBase) + PcdGet32 (PcdOvmfDxeMemFvSize);
+    MemorySize = LowerMemorySize - MemoryBase;
+    if (MemorySize > PeiMemoryCap) {
+      MemoryBase = LowerMemorySize - PeiMemoryCap;
+      MemorySize = PeiMemoryCap;
+    }
+  }
+
+  //
+  // Publish this memory to the PEI Core
+  //
+  Status = PublishSystemMemory(MemoryBase, MemorySize);
+  ASSERT_EFI_ERROR (Status);
+
+  return Status;
+}
+
+
+/**
+  Publish system RAM and reserve memory regions
+
+**/
+VOID
+InitializeRamRegions (
+  VOID
+  )
+{
+  XenPublishRamRegions ();
+
+  if (mBootMode != BOOT_ON_S3_RESUME) {
+    //
+    // Reserve the lock box storage area
+    //
+    // Since this memory range will be used on S3 resume, it must be
+    // reserved as ACPI NVS.
+    //
+    // If S3 is unsupported, then various drivers might still write to the
+    // LockBox area. We ought to prevent DXE from serving allocation requests
+    // such that they would overlap the LockBox storage.
+    //
+    ZeroMem (
+      (VOID*)(UINTN) PcdGet32 (PcdOvmfLockBoxStorageBase),
+      (UINTN) PcdGet32 (PcdOvmfLockBoxStorageSize)
+      );
+    BuildMemoryAllocationHob (
+      (EFI_PHYSICAL_ADDRESS)(UINTN) PcdGet32 (PcdOvmfLockBoxStorageBase),
+      (UINT64)(UINTN) PcdGet32 (PcdOvmfLockBoxStorageSize),
+      EfiBootServicesData
+      );
+  }
+}
diff --git a/OvmfPkg/XenPlatformPei/Platform.c b/OvmfPkg/XenPlatformPei/Platform.c
new file mode 100644
index 0000000000..5809eadb0b
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/Platform.c
@@ -0,0 +1,444 @@
+/**@file
+  Platform PEI driver
+
+  Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2011, Andrei Warkentin <andreiw@motorola.com>
+  Copyright (c) 2019, Citrix Systems, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+//
+// The package level header files this module uses
+//
+#include <PiPei.h>
+
+//
+// The Library classes this module consumes
+//
+#include <Library/BaseLib.h>
+#include <Library/DebugLib.h>
+#include <Library/HobLib.h>
+#include <Library/IoLib.h>
+#include <Library/MemoryAllocationLib.h>
+#include <Library/PcdLib.h>
+#include <Library/PciLib.h>
+#include <Library/PeimEntryPoint.h>
+#include <Library/PeiServicesLib.h>
+#include <Library/ResourcePublicationLib.h>
+#include <Guid/MemoryTypeInformation.h>
+#include <Ppi/MasterBootMode.h>
+#include <IndustryStandard/Pci22.h>
+#include <OvmfPlatforms.h>
+
+#include "Platform.h"
+#include "Cmos.h"
+
+EFI_MEMORY_TYPE_INFORMATION mDefaultMemoryTypeInformation[] = {
+  { EfiACPIMemoryNVS,       0x004 },
+  { EfiACPIReclaimMemory,   0x008 },
+  { EfiReservedMemoryType,  0x004 },
+  { EfiRuntimeServicesData, 0x024 },
+  { EfiRuntimeServicesCode, 0x030 },
+  { EfiBootServicesCode,    0x180 },
+  { EfiBootServicesData,    0xF00 },
+  { EfiMaxMemoryType,       0x000 }
+};
+
+
+EFI_PEI_PPI_DESCRIPTOR   mPpiBootMode[] = {
+  {
+    EFI_PEI_PPI_DESCRIPTOR_PPI | EFI_PEI_PPI_DESCRIPTOR_TERMINATE_LIST,
+    &gEfiPeiMasterBootModePpiGuid,
+    NULL
+  }
+};
+
+
+UINT16 mHostBridgeDevId;
+
+EFI_BOOT_MODE mBootMode = BOOT_WITH_FULL_CONFIGURATION;
+
+
+VOID
+AddIoMemoryBaseSizeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  UINT64                      MemorySize
+  )
+{
+  BuildResourceDescriptorHob (
+    EFI_RESOURCE_MEMORY_MAPPED_IO,
+      EFI_RESOURCE_ATTRIBUTE_PRESENT     |
+      EFI_RESOURCE_ATTRIBUTE_INITIALIZED |
+      EFI_RESOURCE_ATTRIBUTE_UNCACHEABLE |
+      EFI_RESOURCE_ATTRIBUTE_TESTED,
+    MemoryBase,
+    MemorySize
+    );
+}
+
+VOID
+AddReservedMemoryBaseSizeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  UINT64                      MemorySize,
+  BOOLEAN                     Cacheable
+  )
+{
+  BuildResourceDescriptorHob (
+    EFI_RESOURCE_MEMORY_RESERVED,
+      EFI_RESOURCE_ATTRIBUTE_PRESENT     |
+      EFI_RESOURCE_ATTRIBUTE_INITIALIZED |
+      EFI_RESOURCE_ATTRIBUTE_UNCACHEABLE |
+      (Cacheable ?
+       EFI_RESOURCE_ATTRIBUTE_WRITE_COMBINEABLE |
+       EFI_RESOURCE_ATTRIBUTE_WRITE_THROUGH_CACHEABLE |
+       EFI_RESOURCE_ATTRIBUTE_WRITE_BACK_CACHEABLE :
+       0
+       ) |
+      EFI_RESOURCE_ATTRIBUTE_TESTED,
+    MemoryBase,
+    MemorySize
+    );
+}
+
+VOID
+AddIoMemoryRangeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  EFI_PHYSICAL_ADDRESS        MemoryLimit
+  )
+{
+  AddIoMemoryBaseSizeHob (MemoryBase, (UINT64)(MemoryLimit - MemoryBase));
+}
+
+
+VOID
+AddMemoryBaseSizeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  UINT64                      MemorySize
+  )
+{
+  BuildResourceDescriptorHob (
+    EFI_RESOURCE_SYSTEM_MEMORY,
+      EFI_RESOURCE_ATTRIBUTE_PRESENT |
+      EFI_RESOURCE_ATTRIBUTE_INITIALIZED |
+      EFI_RESOURCE_ATTRIBUTE_UNCACHEABLE |
+      EFI_RESOURCE_ATTRIBUTE_WRITE_COMBINEABLE |
+      EFI_RESOURCE_ATTRIBUTE_WRITE_THROUGH_CACHEABLE |
+      EFI_RESOURCE_ATTRIBUTE_WRITE_BACK_CACHEABLE |
+      EFI_RESOURCE_ATTRIBUTE_TESTED,
+    MemoryBase,
+    MemorySize
+    );
+}
+
+
+VOID
+AddMemoryRangeHob (
+  EFI_PHYSICAL_ADDRESS        MemoryBase,
+  EFI_PHYSICAL_ADDRESS        MemoryLimit
+  )
+{
+  AddMemoryBaseSizeHob (MemoryBase, (UINT64)(MemoryLimit - MemoryBase));
+}
+
+
+VOID
+MemMapInitialization (
+  VOID
+  )
+{
+  UINT64        PciIoBase;
+  UINT64        PciIoSize;
+  RETURN_STATUS PcdStatus;
+
+  PciIoBase = 0xC000;
+  PciIoSize = 0x4000;
+
+  //
+  // Create Memory Type Information HOB
+  //
+  BuildGuidDataHob (
+    &gEfiMemoryTypeInformationGuid,
+    mDefaultMemoryTypeInformation,
+    sizeof(mDefaultMemoryTypeInformation)
+    );
+
+  //
+  // Video memory + Legacy BIOS region
+  //
+  AddIoMemoryRangeHob (0x0A0000, BASE_1MB);
+
+  //
+  // Add PCI IO Port space available for PCI resource allocations.
+  //
+  BuildResourceDescriptorHob (
+    EFI_RESOURCE_IO,
+    EFI_RESOURCE_ATTRIBUTE_PRESENT     |
+    EFI_RESOURCE_ATTRIBUTE_INITIALIZED,
+    PciIoBase,
+    PciIoSize
+    );
+  PcdStatus = PcdSet64S (PcdPciIoBase, PciIoBase);
+  ASSERT_RETURN_ERROR (PcdStatus);
+  PcdStatus = PcdSet64S (PcdPciIoSize, PciIoSize);
+  ASSERT_RETURN_ERROR (PcdStatus);
+}
+
+VOID
+PciExBarInitialization (
+  VOID
+  )
+{
+  union {
+    UINT64 Uint64;
+    UINT32 Uint32[2];
+  } PciExBarBase;
+
+  //
+  // We only support the 256MB size for the MMCONFIG area:
+  // 256 buses * 32 devices * 8 functions * 4096 bytes config space.
+  //
+  // The masks used below enforce the Q35 requirements that the MMCONFIG area
+  // be (a) correctly aligned -- here at 256 MB --, (b) located under 64 GB.
+  //
+  // Note that (b) also ensures that the minimum address width we have
+  // determined in AddressWidthInitialization(), i.e., 36 bits, will suffice
+  // for DXE's page tables to cover the MMCONFIG area.
+  //
+  PciExBarBase.Uint64 = FixedPcdGet64 (PcdPciExpressBaseAddress);
+  ASSERT ((PciExBarBase.Uint32[1] & MCH_PCIEXBAR_HIGHMASK) == 0);
+  ASSERT ((PciExBarBase.Uint32[0] & MCH_PCIEXBAR_LOWMASK) == 0);
+
+  //
+  // Clear the PCIEXBAREN bit first, before programming the high register.
+  //
+  PciWrite32 (DRAMC_REGISTER_Q35 (MCH_PCIEXBAR_LOW), 0);
+
+  //
+  // Program the high register. Then program the low register, setting the
+  // MMCONFIG area size and enabling decoding at once.
+  //
+  PciWrite32 (DRAMC_REGISTER_Q35 (MCH_PCIEXBAR_HIGH), PciExBarBase.Uint32[1]);
+  PciWrite32 (
+    DRAMC_REGISTER_Q35 (MCH_PCIEXBAR_LOW),
+    PciExBarBase.Uint32[0] | MCH_PCIEXBAR_BUS_FF | MCH_PCIEXBAR_EN
+    );
+}
+
+VOID
+MiscInitialization (
+  VOID
+  )
+{
+  UINTN         PmCmd;
+  UINTN         Pmba;
+  UINT32        PmbaAndVal;
+  UINT32        PmbaOrVal;
+  UINTN         AcpiCtlReg;
+  UINT8         AcpiEnBit;
+  RETURN_STATUS PcdStatus;
+
+  //
+  // Disable A20 Mask
+  //
+  IoOr8 (0x92, BIT1);
+
+  //
+  // Build the CPU HOB with guest RAM size dependent address width and 16-bits
+  // of IO space. (Side note: unlike other HOBs, the CPU HOB is needed during
+  // S3 resume as well, so we build it unconditionally.)
+  //
+  BuildCpuHob (mPhysMemAddressWidth, 16);
+
+  //
+  // Determine platform type and save Host Bridge DID to PCD
+  //
+  switch (mHostBridgeDevId) {
+    case INTEL_82441_DEVICE_ID:
+      PmCmd      = POWER_MGMT_REGISTER_PIIX4 (PCI_COMMAND_OFFSET);
+      Pmba       = POWER_MGMT_REGISTER_PIIX4 (PIIX4_PMBA);
+      PmbaAndVal = ~(UINT32)PIIX4_PMBA_MASK;
+      PmbaOrVal  = PIIX4_PMBA_VALUE;
+      AcpiCtlReg = POWER_MGMT_REGISTER_PIIX4 (PIIX4_PMREGMISC);
+      AcpiEnBit  = PIIX4_PMREGMISC_PMIOSE;
+      break;
+    case INTEL_Q35_MCH_DEVICE_ID:
+      PmCmd      = POWER_MGMT_REGISTER_Q35 (PCI_COMMAND_OFFSET);
+      Pmba       = POWER_MGMT_REGISTER_Q35 (ICH9_PMBASE);
+      PmbaAndVal = ~(UINT32)ICH9_PMBASE_MASK;
+      PmbaOrVal  = ICH9_PMBASE_VALUE;
+      AcpiCtlReg = POWER_MGMT_REGISTER_Q35 (ICH9_ACPI_CNTL);
+      AcpiEnBit  = ICH9_ACPI_CNTL_ACPI_EN;
+      break;
+    default:
+      DEBUG ((DEBUG_ERROR, "%a: Unknown Host Bridge Device ID: 0x%04x\n",
+        __FUNCTION__, mHostBridgeDevId));
+      ASSERT (FALSE);
+      return;
+  }
+  PcdStatus = PcdSet16S (PcdOvmfHostBridgePciDevId, mHostBridgeDevId);
+  ASSERT_RETURN_ERROR (PcdStatus);
+
+  //
+  // If the appropriate IOspace enable bit is set, assume the ACPI PMBA
+  // has been configured (e.g., by Xen) and skip the setup here.
+  // This matches the logic in AcpiTimerLibConstructor ().
+  //
+  if ((PciRead8 (AcpiCtlReg) & AcpiEnBit) == 0) {
+    //
+    // The PEI phase should be exited with fully accessibe ACPI PM IO space:
+    // 1. set PMBA
+    //
+    PciAndThenOr32 (Pmba, PmbaAndVal, PmbaOrVal);
+
+    //
+    // 2. set PCICMD/IOSE
+    //
+    PciOr8 (PmCmd, EFI_PCI_COMMAND_IO_SPACE);
+
+    //
+    // 3. set ACPI PM IO enable bit (PMREGMISC:PMIOSE or ACPI_CNTL:ACPI_EN)
+    //
+    PciOr8 (AcpiCtlReg, AcpiEnBit);
+  }
+
+  if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
+    //
+    // Set Root Complex Register Block BAR
+    //
+    PciWrite32 (
+      POWER_MGMT_REGISTER_Q35 (ICH9_RCBA),
+      ICH9_ROOT_COMPLEX_BASE | ICH9_RCBA_EN
+      );
+
+    //
+    // Set PCI Express Register Range Base Address
+    //
+    PciExBarInitialization ();
+  }
+}
+
+
+VOID
+BootModeInitialization (
+  VOID
+  )
+{
+  EFI_STATUS    Status;
+
+  if (CmosRead8 (0xF) == 0xFE) {
+    mBootMode = BOOT_ON_S3_RESUME;
+  }
+  CmosWrite8 (0xF, 0x00);
+
+  Status = PeiServicesSetBootMode (mBootMode);
+  ASSERT_EFI_ERROR (Status);
+
+  Status = PeiServicesInstallPpi (mPpiBootMode);
+  ASSERT_EFI_ERROR (Status);
+}
+
+
+VOID
+ReserveEmuVariableNvStore (
+  )
+{
+  EFI_PHYSICAL_ADDRESS VariableStore;
+  RETURN_STATUS        PcdStatus;
+
+  //
+  // Allocate storage for NV variables early on so it will be
+  // at a consistent address.  Since VM memory is preserved
+  // across reboots, this allows the NV variable storage to survive
+  // a VM reboot.
+  //
+  VariableStore =
+    (EFI_PHYSICAL_ADDRESS)(UINTN)
+      AllocateRuntimePages (
+        EFI_SIZE_TO_PAGES (2 * PcdGet32 (PcdFlashNvStorageFtwSpareSize))
+        );
+  DEBUG ((DEBUG_INFO,
+          "Reserved variable store memory: 0x%lX; size: %dkb\n",
+          VariableStore,
+          (2 * PcdGet32 (PcdFlashNvStorageFtwSpareSize)) / 1024
+        ));
+  PcdStatus = PcdSet64S (PcdEmuVariableNvStoreReserved, VariableStore);
+  ASSERT_RETURN_ERROR (PcdStatus);
+}
+
+
+VOID
+DebugDumpCmos (
+  VOID
+  )
+{
+  UINT32 Loop;
+
+  DEBUG ((DEBUG_INFO, "CMOS:\n"));
+
+  for (Loop = 0; Loop < 0x80; Loop++) {
+    if ((Loop % 0x10) == 0) {
+      DEBUG ((DEBUG_INFO, "%02x:", Loop));
+    }
+    DEBUG ((DEBUG_INFO, " %02x", CmosRead8 (Loop)));
+    if ((Loop % 0x10) == 0xf) {
+      DEBUG ((DEBUG_INFO, "\n"));
+    }
+  }
+}
+
+
+
+/**
+  Perform Platform PEI initialization.
+
+  @param  FileHandle      Handle of the file being invoked.
+  @param  PeiServices     Describes the list of possible PEI Services.
+
+  @return EFI_SUCCESS     The PEIM initialized successfully.
+
+**/
+EFI_STATUS
+EFIAPI
+InitializeXenPlatform (
+  IN       EFI_PEI_FILE_HANDLE  FileHandle,
+  IN CONST EFI_PEI_SERVICES     **PeiServices
+  )
+{
+  DEBUG ((DEBUG_INFO, "Platform PEIM Loaded\n"));
+
+  DebugDumpCmos ();
+
+  if (!XenDetect ()) {
+    DEBUG ((DEBUG_ERROR, "ERROR: Xen isn't detected\n"));
+    ASSERT (FALSE);
+    CpuDeadLoop ();
+  }
+
+  BootModeInitialization ();
+  AddressWidthInitialization ();
+
+  //
+  // Query Host Bridge DID
+  //
+  mHostBridgeDevId = PciRead16 (OVMF_HOSTBRIDGE_DID);
+
+  PublishPeiMemory ();
+
+  InitializeRamRegions ();
+
+  InitializeXen ();
+
+  if (mBootMode != BOOT_ON_S3_RESUME) {
+    ReserveEmuVariableNvStore ();
+    PeiFvInitialization ();
+    MemMapInitialization ();
+  }
+
+  InstallClearCacheCallback ();
+  AmdSevInitialize ();
+  MiscInitialization ();
+
+  return EFI_SUCCESS;
+}
diff --git a/OvmfPkg/XenPlatformPei/Xen.c b/OvmfPkg/XenPlatformPei/Xen.c
new file mode 100644
index 0000000000..f4d0d1c73b
--- /dev/null
+++ b/OvmfPkg/XenPlatformPei/Xen.c
@@ -0,0 +1,219 @@
+/**@file
+  Xen Platform PEI support
+
+  Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2011, Andrei Warkentin <andreiw@motorola.com>
+  Copyright (c) 2019, Citrix Systems, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+//
+// The package level header files this module uses
+//
+#include <PiPei.h>
+
+//
+// The Library classes this module consumes
+//
+#include <Library/DebugLib.h>
+#include <Library/HobLib.h>
+#include <Library/MemoryAllocationLib.h>
+#include <Library/PcdLib.h>
+#include <Guid/XenInfo.h>
+#include <IndustryStandard/E820.h>
+#include <Library/ResourcePublicationLib.h>
+#include <Library/MtrrLib.h>
+
+#include "Platform.h"
+#include "Xen.h"
+
+STATIC UINT32 mXenLeaf = 0;
+
+EFI_XEN_INFO mXenInfo;
+
+/**
+  Returns E820 map provided by Xen
+
+  @param Entries      Pointer to E820 map
+  @param Count        Number of entries
+
+  @return EFI_STATUS
+**/
+EFI_STATUS
+XenGetE820Map (
+  EFI_E820_ENTRY64 **Entries,
+  UINT32 *Count
+  )
+{
+  EFI_XEN_OVMF_INFO *Info =
+    (EFI_XEN_OVMF_INFO *)(UINTN) OVMF_INFO_PHYSICAL_ADDRESS;
+
+  if (AsciiStrCmp ((CHAR8 *) Info->Signature, "XenHVMOVMF")) {
+    return EFI_NOT_FOUND;
+  }
+
+  ASSERT (Info->E820 < MAX_ADDRESS);
+  *Entries = (EFI_E820_ENTRY64 *)(UINTN) Info->E820;
+  *Count = Info->E820EntriesCount;
+
+  return EFI_SUCCESS;
+}
+
+/**
+  Connects to the Hypervisor.
+
+  @param  XenLeaf     CPUID index used to connect.
+
+  @return EFI_STATUS
+
+**/
+EFI_STATUS
+XenConnect (
+  UINT32 XenLeaf
+  )
+{
+  UINT32 Index;
+  UINT32 TransferReg;
+  UINT32 TransferPages;
+  UINT32 XenVersion;
+
+  AsmCpuid (XenLeaf + 2, &TransferPages, &TransferReg, NULL, NULL);
+  mXenInfo.HyperPages = AllocatePages (TransferPages);
+  if (!mXenInfo.HyperPages) {
+    return EFI_OUT_OF_RESOURCES;
+  }
+
+  for (Index = 0; Index < TransferPages; Index++) {
+    AsmWriteMsr64 (TransferReg,
+                   (UINTN) mXenInfo.HyperPages +
+                   (Index << EFI_PAGE_SHIFT) + Index);
+  }
+
+  AsmCpuid (XenLeaf + 1, &XenVersion, NULL, NULL, NULL);
+  DEBUG ((DEBUG_ERROR, "Detected Xen version %d.%d\n",
+          XenVersion >> 16, XenVersion & 0xFFFF));
+  mXenInfo.VersionMajor = (UINT16)(XenVersion >> 16);
+  mXenInfo.VersionMinor = (UINT16)(XenVersion & 0xFFFF);
+
+  /* TBD: Locate hvm_info and reserve it away. */
+  mXenInfo.HvmInfo = NULL;
+
+  BuildGuidDataHob (
+    &gEfiXenInfoGuid,
+    &mXenInfo,
+    sizeof(mXenInfo)
+    );
+
+  return EFI_SUCCESS;
+}
+
+/**
+  Figures out if we are running inside Xen HVM.
+
+  @retval TRUE   Xen was detected
+  @retval FALSE  Xen was not detected
+
+**/
+BOOLEAN
+XenDetect (
+  VOID
+  )
+{
+  UINT8 Signature[13];
+
+  if (mXenLeaf != 0) {
+    return TRUE;
+  }
+
+  Signature[12] = '\0';
+  for (mXenLeaf = 0x40000000; mXenLeaf < 0x40010000; mXenLeaf += 0x100) {
+    AsmCpuid (mXenLeaf,
+              NULL,
+              (UINT32 *) &Signature[0],
+              (UINT32 *) &Signature[4],
+              (UINT32 *) &Signature[8]);
+
+    if (!AsciiStrCmp ((CHAR8 *) Signature, "XenVMMXenVMM")) {
+      return TRUE;
+    }
+  }
+
+  mXenLeaf = 0;
+  return FALSE;
+}
+
+
+VOID
+XenPublishRamRegions (
+  VOID
+  )
+{
+  EFI_E820_ENTRY64  *E820Map;
+  UINT32            E820EntriesCount;
+  EFI_STATUS        Status;
+
+  DEBUG ((DEBUG_INFO, "Using memory map provided by Xen\n"));
+
+  //
+  // Parse RAM in E820 map
+  //
+  E820EntriesCount = 0;
+  Status = XenGetE820Map (&E820Map, &E820EntriesCount);
+
+  ASSERT_EFI_ERROR (Status);
+
+  if (E820EntriesCount > 0) {
+    EFI_E820_ENTRY64 *Entry;
+    UINT32 Loop;
+
+    for (Loop = 0; Loop < E820EntriesCount; Loop++) {
+      Entry = E820Map + Loop;
+
+      //
+      // Only care about RAM
+      //
+      if (Entry->Type != EfiAcpiAddressRangeMemory) {
+        continue;
+      }
+
+      AddMemoryBaseSizeHob (Entry->BaseAddr, Entry->Length);
+
+      MtrrSetMemoryAttribute (Entry->BaseAddr, Entry->Length, CacheWriteBack);
+    }
+  }
+}
+
+
+/**
+  Perform Xen PEI initialization.
+
+  @return EFI_SUCCESS     Xen initialized successfully
+  @return EFI_NOT_FOUND   Not running under Xen
+
+**/
+EFI_STATUS
+InitializeXen (
+  VOID
+  )
+{
+  RETURN_STATUS PcdStatus;
+
+  if (mXenLeaf == 0) {
+    return EFI_NOT_FOUND;
+  }
+
+  XenConnect (mXenLeaf);
+
+  //
+  // Reserve away HVMLOADER reserved memory [0xFC000000,0xFD000000).
+  // This needs to match HVMLOADER RESERVED_MEMBASE/RESERVED_MEMSIZE.
+  //
+  AddReservedMemoryBaseSizeHob (0xFC000000, 0x1000000, FALSE);
+
+  PcdStatus = PcdSetBoolS (PcdPciDisableBusEnumeration, TRUE);
+  ASSERT_RETURN_ERROR (PcdStatus);
+
+  return EFI_SUCCESS;
+}
diff --git a/Maintainers.txt b/Maintainers.txt
index 34bdb275b4..42ec8d54af 100644
--- a/Maintainers.txt
+++ b/Maintainers.txt
@@ -379,6 +379,7 @@ F: OvmfPkg/PlatformPei/Xen.*
 F: OvmfPkg/SmbiosPlatformDxe/*Xen.c
 F: OvmfPkg/XenBusDxe/
 F: OvmfPkg/XenIoPciDxe/
+F: OvmfPkg/XenPlatformPei/
 F: OvmfPkg/XenPvBlkDxe/
 F: OvmfPkg/XenResetVector/
 R: Anthony Perard <anthony.perard@citrix.com>
