source: vbox/trunk/src/VBox/Devices/EFI/FirmwareNew/OvmfPkg/PlatformPei/MemDetect.c@ 80721

/**@file
  Memory Detection for Virtual Machines.

  Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
  SPDX-License-Identifier: BSD-2-Clause-Patent

Module Name:

  MemDetect.c

**/

//
// The package level header files this module uses
//
#include <IndustryStandard/E820.h>
#include <IndustryStandard/I440FxPiix4.h>
#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 <Library/MtrrLib.h>
#include <Library/QemuFwCfgLib.h>

#include "Platform.h"
#include "Cmos.h"

UINT8 mPhysMemAddressWidth;

STATIC UINT32 mS3AcpiReservedMemoryBase;
STATIC UINT32 mS3AcpiReservedMemorySize;

STATIC UINT16 mQ35TsegMbytes;

UINT32 mQemuUc32Base;

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;
}


VOID
QemuUc32BaseInitialization (
  VOID
  )
{
  UINT32 LowerMemorySize;
  UINT32 Uc32Size;

  if (mXen) {
    return;
  }

  if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
    //
    // On q35, the 32-bit area that we'll mark as UC, through variable MTRRs,
    // starts at PcdPciExpressBaseAddress. The platform DSC is responsible for
    // setting PcdPciExpressBaseAddress such that describing the
    // [PcdPciExpressBaseAddress, 4GB) range require a very small number of
    // variable MTRRs (preferably 1 or 2).
    //
#ifndef VBOX
    ASSERT (FixedPcdGet64 (PcdPciExpressBaseAddress) <= MAX_UINT32);
    mQemuUc32Base = (UINT32)FixedPcdGet64 (PcdPciExpressBaseAddress);
#else
    ASSERT (PcdGet64 (PcdPciExpressBaseAddress) <= MAX_UINT32);
    mQemuUc32Base = (UINT32)PcdGet64 (PcdPciExpressBaseAddress);
#endif
    return;
  }

  ASSERT (mHostBridgeDevId == INTEL_82441_DEVICE_ID);
  //
  // On i440fx, start with the [LowerMemorySize, 4GB) range. Make sure one
  // variable MTRR suffices by truncating the size to a whole power of two,
  // while keeping the end affixed to 4GB. This will round the base up.
  //
  LowerMemorySize = GetSystemMemorySizeBelow4gb ();
  Uc32Size = GetPowerOfTwo32 ((UINT32)(SIZE_4GB - LowerMemorySize));
  mQemuUc32Base = (UINT32)(SIZE_4GB - Uc32Size);
  //
  // Assuming that LowerMemorySize is at least 1 byte, Uc32Size is at most 2GB.
  // Therefore mQemuUc32Base is at least 2GB.
  //
  ASSERT (mQemuUc32Base >= BASE_2GB);

  if (mQemuUc32Base != LowerMemorySize) {
    DEBUG ((DEBUG_VERBOSE, "%a: rounded UC32 base from 0x%x up to 0x%x, for "
      "an UC32 size of 0x%x\n", __FUNCTION__, LowerMemorySize, mQemuUc32Base,
      Uc32Size));
  }
}


/**
  Iterate over the RAM entries in QEMU's fw_cfg E820 RAM map that start outside
  of the 32-bit address range.

  Find the highest exclusive >=4GB RAM address, or produce memory resource
  descriptor HOBs for RAM entries that start at or above 4GB.

  @param[out] MaxAddress  If MaxAddress is NULL, then ScanOrAdd64BitE820Ram()
                          produces memory resource descriptor HOBs for RAM
                          entries that start at or above 4GB.

                          Otherwise, MaxAddress holds the highest exclusive
                          >=4GB RAM address on output. If QEMU's fw_cfg E820
                          RAM map contains no RAM entry that starts outside of
                          the 32-bit address range, then MaxAddress is exactly
                          4GB on output.

  @retval EFI_SUCCESS         The fw_cfg E820 RAM map was found and processed.

  @retval EFI_PROTOCOL_ERROR  The RAM map was found, but its size wasn't a
                              whole multiple of sizeof(EFI_E820_ENTRY64). No
                              RAM entry was processed.

  @return                     Error codes from QemuFwCfgFindFile(). No RAM
                              entry was processed.
**/
STATIC
EFI_STATUS
ScanOrAdd64BitE820Ram (
  OUT UINT64 *MaxAddress OPTIONAL
  )
{
  EFI_STATUS           Status;
  FIRMWARE_CONFIG_ITEM FwCfgItem;
  UINTN                FwCfgSize;
  EFI_E820_ENTRY64     E820Entry;
  UINTN                Processed;

  Status = QemuFwCfgFindFile ("etc/e820", &FwCfgItem, &FwCfgSize);
  if (EFI_ERROR (Status)) {
    return Status;
  }
  if (FwCfgSize % sizeof E820Entry != 0) {
    return EFI_PROTOCOL_ERROR;
  }

  if (MaxAddress != NULL) {
    *MaxAddress = BASE_4GB;
  }

  QemuFwCfgSelectItem (FwCfgItem);
  for (Processed = 0; Processed < FwCfgSize; Processed += sizeof E820Entry) {
    QemuFwCfgReadBytes (sizeof E820Entry, &E820Entry);
    DEBUG ((
      DEBUG_VERBOSE,
      "%a: Base=0x%Lx Length=0x%Lx Type=%u\n",
      __FUNCTION__,
      E820Entry.BaseAddr,
      E820Entry.Length,
      E820Entry.Type
      ));
    if (E820Entry.Type == EfiAcpiAddressRangeMemory &&
        E820Entry.BaseAddr >= BASE_4GB) {
      if (MaxAddress == NULL) {
        UINT64 Base;
        UINT64 End;

        //
        // Round up the start address, and round down the end address.
        //
        Base = ALIGN_VALUE (E820Entry.BaseAddr, (UINT64)EFI_PAGE_SIZE);
        End = (E820Entry.BaseAddr + E820Entry.Length) &
              ~(UINT64)EFI_PAGE_MASK;
        if (Base < End) {
          AddMemoryRangeHob (Base, End);
          DEBUG ((
            DEBUG_VERBOSE,
            "%a: AddMemoryRangeHob [0x%Lx, 0x%Lx)\n",
            __FUNCTION__,
            Base,
            End
            ));
        }
      } else {
        UINT64 Candidate;

        Candidate = E820Entry.BaseAddr + E820Entry.Length;
        if (Candidate > *MaxAddress) {
          *MaxAddress = Candidate;
          DEBUG ((
            DEBUG_VERBOSE,
            "%a: MaxAddress=0x%Lx\n",
            __FUNCTION__,
            *MaxAddress
            ));
        }
      }
    }
  }
  return EFI_SUCCESS;
}


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;
  CHAR8                MbString[7 + 1];
  EFI_STATUS           Status;
  FIRMWARE_CONFIG_ITEM FwCfgItem;
  UINTN                FwCfgSize;
  UINT64               HotPlugMemoryEnd;
  RETURN_STATUS        PcdStatus;

  //
  // set FirstNonAddress to suppress incorrect compiler/analyzer warnings
  //
  FirstNonAddress = 0;

  //
  // If QEMU presents an E820 map, then get the highest exclusive >=4GB RAM
  // address from it. This can express an address >= 4GB+1TB.
  //
  // Otherwise, get the flat size of the memory above 4GB from the CMOS (which
  // can only express a size smaller than 1TB), and add it to 4GB.
  //
  Status = ScanOrAdd64BitE820Ram (&FirstNonAddress);
  if (EFI_ERROR (Status)) {
    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);

  //
  // See if the user specified the number of megabytes for the 64-bit PCI host
  // aperture. The number of non-NUL characters in MbString allows for
  // 9,999,999 MB, which is approximately 10 TB.
  //
  // As signaled by the "X-" prefix, this knob is experimental, and might go
  // away at any time.
  //
  Status = QemuFwCfgFindFile ("opt/ovmf/X-PciMmio64Mb", &FwCfgItem,
             &FwCfgSize);
  if (!EFI_ERROR (Status)) {
    if (FwCfgSize >= sizeof MbString) {
      DEBUG ((EFI_D_WARN,
        "%a: ignoring malformed 64-bit PCI host aperture size from fw_cfg\n",
        __FUNCTION__));
    } else {
      QemuFwCfgSelectItem (FwCfgItem);
      QemuFwCfgReadBytes (FwCfgSize, MbString);
      MbString[FwCfgSize] = '\0';
      Pci64Size = LShiftU64 (AsciiStrDecimalToUint64 (MbString), 20);
    }
  }

  if (Pci64Size == 0) {
    if (mBootMode != BOOT_ON_S3_RESUME) {
      DEBUG ((EFI_D_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;
  }

  //
  // The "etc/reserved-memory-end" fw_cfg file, when present, contains an
  // absolute, exclusive end address for the memory hotplug area. This area
  // starts right at the end of the memory above 4GB. The 64-bit PCI host
  // aperture must be placed above it.
  //
  Status = QemuFwCfgFindFile ("etc/reserved-memory-end", &FwCfgItem,
             &FwCfgSize);
  if (!EFI_ERROR (Status) && FwCfgSize == sizeof HotPlugMemoryEnd) {
    QemuFwCfgSelectItem (FwCfgItem);
    QemuFwCfgReadBytes (FwCfgSize, &HotPlugMemoryEnd);
    DEBUG ((DEBUG_VERBOSE, "%a: HotPlugMemoryEnd=0x%Lx\n", __FUNCTION__,
      HotPlugMemoryEnd));

    ASSERT (HotPlugMemoryEnd >= FirstNonAddress);
    FirstNonAddress = HotPlugMemoryEnd;
  }

  //
  // 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 ((EFI_D_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 (FeaturePcdGet (PcdSmmSmramRequire)) {
    //
    // TSEG is chipped from the end of low RAM
    //
    LowerMemorySize -= mQ35TsegMbytes * SIZE_1MB;
  }

  //
  // If S3 is supported, then the S3 permanent PEI memory is placed next,
  // downwards. Its size is primarily dictated by CpuMpPei. The formula below
  // is an approximation.
  //
  if (mS3Supported) {
    mS3AcpiReservedMemorySize = SIZE_512KB +
      mMaxCpuCount *
      PcdGet32 (PcdCpuApStackSize);
    mS3AcpiReservedMemoryBase = LowerMemorySize - mS3AcpiReservedMemorySize;
    LowerMemorySize = mS3AcpiReservedMemoryBase;
  }

  if (mBootMode == BOOT_ON_S3_RESUME) {
    MemoryBase = mS3AcpiReservedMemoryBase;
    MemorySize = mS3AcpiReservedMemorySize;
  } else {
    PeiMemoryCap = GetPeiMemoryCap ();
    DEBUG ((EFI_D_INFO, "%a: mPhysMemAddressWidth=%d PeiMemoryCap=%u KB\n",
      __FUNCTION__, mPhysMemAddressWidth, PeiMemoryCap >> 10));

    //
    // Determine the range of memory to use during PEI
    //
    // Technically we could lay the permanent PEI RAM over SEC's temporary
    // decompression and scratch buffer even if "secure S3" is needed, since
    // their lifetimes don't overlap. However, PeiFvInitialization() will cover
    // RAM up to PcdOvmfDecompressionScratchEnd with an EfiACPIMemoryNVS memory
    // allocation HOB, and other allocations served from the permanent PEI RAM
    // shouldn't overlap with that HOB.
    //
    MemoryBase = mS3Supported && FeaturePcdGet (PcdSmmSmramRequire) ?
      PcdGet32 (PcdOvmfDecompressionScratchEnd) :
      PcdGet32 (PcdOvmfDxeMemFvBase) + PcdGet32 (PcdOvmfDxeMemFvSize);
    MemorySize = LowerMemorySize - MemoryBase;
    if (MemorySize > PeiMemoryCap) {
      MemoryBase = LowerMemorySize - PeiMemoryCap;
      MemorySize = PeiMemoryCap;
    }
  }
#ifdef VBOX
  MemorySize -= BASE_64KB; /* Reserves 64KB for ACPI tables. */
#endif

  //
  // Publish this memory to the PEI Core
  //
  Status = PublishSystemMemory(MemoryBase, MemorySize);
  ASSERT_EFI_ERROR (Status);

  return Status;
}


#ifndef VBOX
/**
  Peform Memory Detection for QEMU / KVM

**/
STATIC
VOID
QemuInitializeRam (
  VOID
  )
{
  UINT64                      LowerMemorySize;
  UINT64                      UpperMemorySize;
  MTRR_SETTINGS               MtrrSettings;
  EFI_STATUS                  Status;

  DEBUG ((EFI_D_INFO, "%a called\n", __FUNCTION__));

  //
  // Determine total memory size available
  //
  LowerMemorySize = GetSystemMemorySizeBelow4gb ();
  UpperMemorySize = GetSystemMemorySizeAbove4gb ();

  if (mBootMode == BOOT_ON_S3_RESUME) {
    //
    // Create the following memory HOB as an exception on the S3 boot path.
    //
    // Normally we'd create memory HOBs only on the normal boot path. However,
    // CpuMpPei specifically needs such a low-memory HOB on the S3 path as
    // well, for "borrowing" a subset of it temporarily, for the AP startup
    // vector.
    //
    // CpuMpPei saves the original contents of the borrowed area in permanent
    // PEI RAM, in a backup buffer allocated with the normal PEI services.
    // CpuMpPei restores the original contents ("returns" the borrowed area) at
    // End-of-PEI. End-of-PEI in turn is emitted by S3Resume2Pei before
    // transferring control to the OS's wakeup vector in the FACS.
    //
    // We expect any other PEIMs that "borrow" memory similarly to CpuMpPei to
    // restore the original contents. Furthermore, we expect all such PEIMs
    // (CpuMpPei included) to claim the borrowed areas by producing memory
    // allocation HOBs, and to honor preexistent memory allocation HOBs when
    // looking for an area to borrow.
    //
    AddMemoryRangeHob (0, BASE_512KB + BASE_128KB);
  } else {
    //
    // Create memory HOBs
    //
    AddMemoryRangeHob (0, BASE_512KB + BASE_128KB);

    if (FeaturePcdGet (PcdSmmSmramRequire)) {
      UINT32 TsegSize;

      TsegSize = mQ35TsegMbytes * SIZE_1MB;
      AddMemoryRangeHob (BASE_1MB, LowerMemorySize - TsegSize);
      AddReservedMemoryBaseSizeHob (LowerMemorySize - TsegSize, TsegSize,
        TRUE);
    } else {
      AddMemoryRangeHob (BASE_1MB, LowerMemorySize);
    }

    //
    // If QEMU presents an E820 map, then create memory HOBs for the >=4GB RAM
    // entries. Otherwise, create a single memory HOB with the flat >=4GB
    // memory size read from the CMOS.
    //
    Status = ScanOrAdd64BitE820Ram (NULL);
    if (EFI_ERROR (Status) && UpperMemorySize != 0) {
      AddMemoryBaseSizeHob (BASE_4GB, UpperMemorySize);
    }
  }

  //
  // We'd like to keep the following ranges uncached:
  // - [640 KB, 1 MB)
  // - [LowerMemorySize, 4 GB)
  //
  // Everything else should be WB. Unfortunately, programming the inverse (ie.
  // keeping the default UC, and configuring the complement set of the above as
  // WB) is not reliable in general, because the end of the upper RAM can have
  // practically any alignment, and we may not have enough variable MTRRs to
  // cover it exactly.
  //
  if (IsMtrrSupported ()) {
    MtrrGetAllMtrrs (&MtrrSettings);

    //
    // MTRRs disabled, fixed MTRRs disabled, default type is uncached
    //
    ASSERT ((MtrrSettings.MtrrDefType & BIT11) == 0);
    ASSERT ((MtrrSettings.MtrrDefType & BIT10) == 0);
    ASSERT ((MtrrSettings.MtrrDefType & 0xFF) == 0);

    //
    // flip default type to writeback
    //
    SetMem (&MtrrSettings.Fixed, sizeof MtrrSettings.Fixed, 0x06);
    ZeroMem (&MtrrSettings.Variables, sizeof MtrrSettings.Variables);
    MtrrSettings.MtrrDefType |= BIT11 | BIT10 | 6;
    MtrrSetAllMtrrs (&MtrrSettings);

    //
    // Set memory range from 640KB to 1MB to uncacheable
    //
    Status = MtrrSetMemoryAttribute (BASE_512KB + BASE_128KB,
               BASE_1MB - (BASE_512KB + BASE_128KB), CacheUncacheable);
    ASSERT_EFI_ERROR (Status);

    //
    // Set the memory range from the start of the 32-bit MMIO area (32-bit PCI
    // MMIO aperture on i440fx, PCIEXBAR on q35) to 4GB as uncacheable.
    //
    Status = MtrrSetMemoryAttribute (mQemuUc32Base, SIZE_4GB - mQemuUc32Base,
               CacheUncacheable);
    ASSERT_EFI_ERROR (Status);
  }
}
#else
VOID
VBoxInitializeRam (
  VOID
  )
{
  UINT64                      LowerMemorySize;
  UINT64                      UpperMemorySize;
  EFI_PHYSICAL_ADDRESS        MemoryBase;
  UINT64                      MemorySize;

  DEBUG ((EFI_D_INFO, "%a called\n", __FUNCTION__));

  //
  // Determine total memory size available
  //
  LowerMemorySize = GetSystemMemorySizeBelow4gb ();
  UpperMemorySize = GetSystemMemorySizeAbove4gb ();

  if (mBootMode == BOOT_ON_S3_RESUME) {
    //
    // Create the following memory HOB as an exception on the S3 boot path.
    //
    // Normally we'd create memory HOBs only on the normal boot path. However,
    // CpuMpPei specifically needs such a low-memory HOB on the S3 path as
    // well, for "borrowing" a subset of it temporarily, for the AP startup
    // vector.
    //
    // CpuMpPei saves the original contents of the borrowed area in permanent
    // PEI RAM, in a backup buffer allocated with the normal PEI services.
    // CpuMpPei restores the original contents ("returns" the borrowed area) at
    // End-of-PEI. End-of-PEI in turn is emitted by S3Resume2Pei before
    // transferring control to the OS's wakeup vector in the FACS.
    //
    // We expect any other PEIMs that "borrow" memory similarly to CpuMpPei to
    // restore the original contents. Furthermore, we expect all such PEIMs
    // (CpuMpPei included) to claim the borrowed areas by producing memory
    // allocation HOBs, and to honor preexistent memory allocation HOBs when
    // looking for an area to borrow.
    //
    AddMemoryRangeHob (0, BASE_512KB + BASE_128KB);
    MemoryBase = 0;
    MemorySize = BASE_512KB + BASE_128KB;
  } else {
    LowerMemorySize = GetSystemMemorySizeBelow4gb ();
  }
  LowerMemorySize -= BASE_64KB; /* Reserves 64KB for ACPI tables. */

  //
  // Create memory HOBs
  //
  AddMemoryRangeHob (BASE_1MB, LowerMemorySize);
  MtrrSetMemoryAttribute (BASE_1MB, LowerMemorySize - BASE_1MB, CacheWriteBack);
  AddMemoryRangeHob (0, BASE_512KB + BASE_128KB);
  MtrrSetMemoryAttribute (0, BASE_512KB + BASE_128KB, CacheWriteBack);

  if (UpperMemorySize != 0) {
    AddMemoryBaseSizeHob (BASE_4GB, UpperMemorySize);

    MtrrSetMemoryAttribute (BASE_4GB, UpperMemorySize, CacheWriteBack);
  }
}
#endif

/**
  Publish system RAM and reserve memory regions

**/
VOID
InitializeRamRegions (
  VOID
  )
{
#ifndef VBOX
  if (!mXen) {
    QemuInitializeRam ();
  } else {
    XenPublishRamRegions ();
  }
#else
  VBoxInitializeRam();
#endif

  if (mS3Supported && mBootMode != BOOT_ON_S3_RESUME) {
    //
    // This is the memory range that will be used for PEI on S3 resume
    //
    BuildMemoryAllocationHob (
      mS3AcpiReservedMemoryBase,
      mS3AcpiReservedMemorySize,
      EfiACPIMemoryNVS
      );

    //
    // Cover the initial RAM area used as stack and temporary PEI heap.
    //
    // This is reserved as ACPI NVS so it can be used on S3 resume.
    //
    BuildMemoryAllocationHob (
      PcdGet32 (PcdOvmfSecPeiTempRamBase),
      PcdGet32 (PcdOvmfSecPeiTempRamSize),
      EfiACPIMemoryNVS
      );

    //
    // SEC stores its table of GUIDed section handlers here.
    //
    BuildMemoryAllocationHob (
      PcdGet64 (PcdGuidedExtractHandlerTableAddress),
      PcdGet32 (PcdGuidedExtractHandlerTableSize),
      EfiACPIMemoryNVS
      );

#ifdef MDE_CPU_X64
    //
    // Reserve the initial page tables built by the reset vector code.
    //
    // Since this memory range will be used by the Reset Vector on S3
    // resume, it must be reserved as ACPI NVS.
    //
    BuildMemoryAllocationHob (
      (EFI_PHYSICAL_ADDRESS)(UINTN) PcdGet32 (PcdOvmfSecPageTablesBase),
      (UINT64)(UINTN) PcdGet32 (PcdOvmfSecPageTablesSize),
      EfiACPIMemoryNVS
      );
#endif
  }

  if (mBootMode != BOOT_ON_S3_RESUME) {
    if (!FeaturePcdGet (PcdSmmSmramRequire)) {
      //
      // 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),
        mS3Supported ? EfiACPIMemoryNVS : EfiBootServicesData
        );
    }

    if (FeaturePcdGet (PcdSmmSmramRequire)) {
      UINT32 TsegSize;

      //
      // Make sure the TSEG area that we reported as a reserved memory resource
      // cannot be used for reserved memory allocations.
      //
      TsegSize = mQ35TsegMbytes * SIZE_1MB;
      BuildMemoryAllocationHob (
        GetSystemMemorySizeBelow4gb() - TsegSize,
        TsegSize,
        EfiReservedMemoryType
        );
    }
  }
}