audk/OvmfPkg/PlatformPei/Platform.c

/**@file
  Platform PEI driver

  Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
  Copyright (c) 2011, Andrei Warkentin <andreiw@motorola.com>

  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/QemuFwCfgLib.h>
#include <Library/QemuFwCfgS3Lib.h>
#include <Library/QemuFwCfgSimpleParserLib.h>
#include <Library/ResourcePublicationLib.h>
#include <Ppi/MasterBootMode.h>
#include <IndustryStandard/I440FxPiix4.h>
#include <IndustryStandard/Microvm.h>
#include <IndustryStandard/Pci22.h>
#include <IndustryStandard/Q35MchIch9.h>
#include <IndustryStandard/QemuCpuHotplug.h>
#include <OvmfPlatforms.h>

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

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;

BOOLEAN mS3Supported = FALSE;

UINT32 mMaxCpuCount;

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;
  UINT32        TopOfLowRam;
  UINT64        PciExBarBase;
  UINT32        PciBase;
  UINT32        PciSize;

  PciIoBase = 0xC000;
  PciIoSize = 0x4000;

  //
  // Video memory + Legacy BIOS region
  //
  AddIoMemoryRangeHob (0x0A0000, BASE_1MB);

  if (mHostBridgeDevId == 0xffff /* microvm */) {
    AddIoMemoryBaseSizeHob (MICROVM_GED_MMIO_BASE, SIZE_4KB);
    AddIoMemoryBaseSizeHob (0xFEC00000, SIZE_4KB); /* ioapic #1 */
    AddIoMemoryBaseSizeHob (0xFEC10000, SIZE_4KB); /* ioapic #2 */
    return;
  }

  TopOfLowRam = GetSystemMemorySizeBelow4gb ();
  PciExBarBase = 0;
  if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
    //
    // The MMCONFIG area is expected to fall between the top of low RAM and
    // the base of the 32-bit PCI host aperture.
    //
    PciExBarBase = FixedPcdGet64 (PcdPciExpressBaseAddress);
    ASSERT (TopOfLowRam <= PciExBarBase);
    ASSERT (PciExBarBase <= MAX_UINT32 - SIZE_256MB);
    PciBase = (UINT32)(PciExBarBase + SIZE_256MB);
  } else {
    ASSERT (TopOfLowRam <= mQemuUc32Base);
    PciBase = mQemuUc32Base;
  }

  //
  // address       purpose   size
  // ------------  --------  -------------------------
  // max(top, 2g)  PCI MMIO  0xFC000000 - max(top, 2g)
  // 0xFC000000    gap                           44 MB
  // 0xFEC00000    IO-APIC                        4 KB
  // 0xFEC01000    gap                         1020 KB
  // 0xFED00000    HPET                           1 KB
  // 0xFED00400    gap                          111 KB
  // 0xFED1C000    gap (PIIX4) / RCRB (ICH9)     16 KB
  // 0xFED20000    gap                          896 KB
  // 0xFEE00000    LAPIC                          1 MB
  //
  PciSize = 0xFC000000 - PciBase;
  AddIoMemoryBaseSizeHob (PciBase, PciSize);
  PcdStatus = PcdSet64S (PcdPciMmio32Base, PciBase);
  ASSERT_RETURN_ERROR (PcdStatus);
  PcdStatus = PcdSet64S (PcdPciMmio32Size, PciSize);
  ASSERT_RETURN_ERROR (PcdStatus);

  AddIoMemoryBaseSizeHob (0xFEC00000, SIZE_4KB);
  AddIoMemoryBaseSizeHob (0xFED00000, SIZE_1KB);
  if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
    AddIoMemoryBaseSizeHob (ICH9_ROOT_COMPLEX_BASE, SIZE_16KB);
    //
    // Note: there should be an
    //
    //   AddIoMemoryBaseSizeHob (PciExBarBase, SIZE_256MB);
    //
    // call below, just like the one above for RCBA. However, Linux insists
    // that the MMCONFIG area be marked in the E820 or UEFI memory map as
    // "reserved memory" -- Linux does not content itself with a simple gap
    // in the memory map wherever the MCFG ACPI table points to.
    //
    // This appears to be a safety measure. The PCI Firmware Specification
    // (rev 3.1) says in 4.1.2. "MCFG Table Description": "The resources can
    // *optionally* be returned in [...] EFIGetMemoryMap as reserved memory
    // [...]". (Emphasis added here.)
    //
    // Normally we add memory resource descriptor HOBs in
    // QemuInitializeRam(), and pre-allocate from those with memory
    // allocation HOBs in InitializeRamRegions(). However, the MMCONFIG area
    // is most definitely not RAM; so, as an exception, cover it with
    // uncacheable reserved memory right here.
    //
    AddReservedMemoryBaseSizeHob (PciExBarBase, SIZE_256MB, FALSE);
    BuildMemoryAllocationHob (PciExBarBase, SIZE_256MB,
      EfiReservedMemoryType);
  }
  AddIoMemoryBaseSizeHob (PcdGet32(PcdCpuLocalApicBaseAddress), SIZE_1MB);

  //
  // On Q35, the IO Port space is available for PCI resource allocations from
  // 0x6000 up.
  //
  if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
    PciIoBase = 0x6000;
    PciIoSize = 0xA000;
    ASSERT ((ICH9_PMBASE_VALUE & 0xF000) < PciIoBase);
  }

  //
  // 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);
}

#define UPDATE_BOOLEAN_PCD_FROM_FW_CFG(TokenName)                   \
          do {                                                      \
            BOOLEAN       Setting;                                  \
            RETURN_STATUS PcdStatus;                                \
                                                                    \
            if (!RETURN_ERROR (QemuFwCfgParseBool (                 \
                              "opt/ovmf/" #TokenName, &Setting))) { \
              PcdStatus = PcdSetBoolS (TokenName, Setting);         \
              ASSERT_RETURN_ERROR (PcdStatus);                      \
            }                                                       \
          } while (0)

VOID
NoexecDxeInitialization (
  VOID
  )
{
  UPDATE_BOOLEAN_PCD_FROM_FW_CFG (PcdSetNxForStack);
}

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;
    case 0xffff: /* microvm */
      DEBUG ((DEBUG_INFO, "%a: microvm\n", __FUNCTION__));
      PcdStatus = PcdSet16S (PcdOvmfHostBridgePciDevId,
                             MICROVM_PSEUDO_DEVICE_ID);
      ASSERT_RETURN_ERROR (PcdStatus);
      return;
    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 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"));
    }
  }
}


VOID
S3Verification (
  VOID
  )
{
#if defined (MDE_CPU_X64)
  if (FeaturePcdGet (PcdSmmSmramRequire) && mS3Supported) {
    DEBUG ((DEBUG_ERROR,
      "%a: S3Resume2Pei doesn't support X64 PEI + SMM yet.\n", __FUNCTION__));
    DEBUG ((DEBUG_ERROR,
      "%a: Please disable S3 on the QEMU command line (see the README),\n",
      __FUNCTION__));
    DEBUG ((DEBUG_ERROR,
      "%a: or build OVMF with \"OvmfPkgIa32X64.dsc\".\n", __FUNCTION__));
    ASSERT (FALSE);
    CpuDeadLoop ();
  }
#endif
}


VOID
Q35BoardVerification (
  VOID
  )
{
  if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
    return;
  }

  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 ();
}


/**
  Fetch the boot CPU count and the possible CPU count from QEMU, and expose
  them to UefiCpuPkg modules. Set the mMaxCpuCount variable.
**/
VOID
MaxCpuCountInitialization (
  VOID
  )
{
  UINT16        BootCpuCount;
  RETURN_STATUS PcdStatus;

  //
  // Try to fetch the boot CPU count.
  //
  QemuFwCfgSelectItem (QemuFwCfgItemSmpCpuCount);
  BootCpuCount = QemuFwCfgRead16 ();
  if (BootCpuCount == 0) {
    //
    // QEMU doesn't report the boot CPU count. (BootCpuCount == 0) will let
    // MpInitLib count APs up to (PcdCpuMaxLogicalProcessorNumber - 1), or
    // until PcdCpuApInitTimeOutInMicroSeconds elapses (whichever is reached
    // first).
    //
    DEBUG ((DEBUG_WARN, "%a: boot CPU count unavailable\n", __FUNCTION__));
    mMaxCpuCount = PcdGet32 (PcdCpuMaxLogicalProcessorNumber);
  } else {
    //
    // We will expose BootCpuCount to MpInitLib. MpInitLib will count APs up to
    // (BootCpuCount - 1) precisely, regardless of timeout.
    //
    // Now try to fetch the possible CPU count.
    //
    UINTN CpuHpBase;
    UINT32 CmdData2;

    CpuHpBase = ((mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) ?
                 ICH9_CPU_HOTPLUG_BASE : PIIX4_CPU_HOTPLUG_BASE);

    //
    // If only legacy mode is available in the CPU hotplug register block, or
    // the register block is completely missing, then the writes below are
    // no-ops.
    //
    // 1. Switch the hotplug register block to modern mode.
    //
    IoWrite32 (CpuHpBase + QEMU_CPUHP_W_CPU_SEL, 0);
    //
    // 2. Select a valid CPU for deterministic reading of
    //    QEMU_CPUHP_R_CMD_DATA2.
    //
    //    CPU#0 is always valid; it is the always present and non-removable
    //    BSP.
    //
    IoWrite32 (CpuHpBase + QEMU_CPUHP_W_CPU_SEL, 0);
    //
    // 3. Send a command after which QEMU_CPUHP_R_CMD_DATA2 is specified to
    //    read as zero, and which does not invalidate the selector. (The
    //    selector may change, but it must not become invalid.)
    //
    //    Send QEMU_CPUHP_CMD_GET_PENDING, as it will prove useful later.
    //
    IoWrite8 (CpuHpBase + QEMU_CPUHP_W_CMD, QEMU_CPUHP_CMD_GET_PENDING);
    //
    // 4. Read QEMU_CPUHP_R_CMD_DATA2.
    //
    //    If the register block is entirely missing, then this is an unassigned
    //    IO read, returning all-bits-one.
    //
    //    If only legacy mode is available, then bit#0 stands for CPU#0 in the
    //    "CPU present bitmap". CPU#0 is always present.
    //
    //    Otherwise, QEMU_CPUHP_R_CMD_DATA2 is either still reserved (returning
    //    all-bits-zero), or it is specified to read as zero after the above
    //    steps. Both cases confirm modern mode.
    //
    CmdData2 = IoRead32 (CpuHpBase + QEMU_CPUHP_R_CMD_DATA2);
    DEBUG ((DEBUG_VERBOSE, "%a: CmdData2=0x%x\n", __FUNCTION__, CmdData2));
    if (CmdData2 != 0) {
      //
      // QEMU doesn't support the modern CPU hotplug interface. Assume that the
      // possible CPU count equals the boot CPU count (precluding hotplug).
      //
      DEBUG ((DEBUG_WARN, "%a: modern CPU hotplug interface unavailable\n",
        __FUNCTION__));
      mMaxCpuCount = BootCpuCount;
    } else {
      //
      // Grab the possible CPU count from the modern CPU hotplug interface.
      //
      UINT32 Present, Possible, Selected;

      Present = 0;
      Possible = 0;

      //
      // We've sent QEMU_CPUHP_CMD_GET_PENDING last; this ensures
      // QEMU_CPUHP_RW_CMD_DATA can now be read usefully. However,
      // QEMU_CPUHP_CMD_GET_PENDING may have selected a CPU with actual pending
      // hotplug events; therefore, select CPU#0 forcibly.
      //
      IoWrite32 (CpuHpBase + QEMU_CPUHP_W_CPU_SEL, Possible);

      do {
        UINT8 CpuStatus;

        //
        // Read the status of the currently selected CPU. This will help with a
        // sanity check against "BootCpuCount".
        //
        CpuStatus = IoRead8 (CpuHpBase + QEMU_CPUHP_R_CPU_STAT);
        if ((CpuStatus & QEMU_CPUHP_STAT_ENABLED) != 0) {
          ++Present;
        }
        //
        // Attempt to select the next CPU.
        //
        ++Possible;
        IoWrite32 (CpuHpBase + QEMU_CPUHP_W_CPU_SEL, Possible);
        //
        // If the selection is successful, then the following read will return
        // the selector (which we know is positive at this point). Otherwise,
        // the read will return 0.
        //
        Selected = IoRead32 (CpuHpBase + QEMU_CPUHP_RW_CMD_DATA);
        ASSERT (Selected == Possible || Selected == 0);
      } while (Selected > 0);

      //
      // Sanity check: fw_cfg and the modern CPU hotplug interface should
      // return the same boot CPU count.
      //
      if (BootCpuCount != Present) {
        DEBUG ((DEBUG_WARN, "%a: QEMU v2.7 reset bug: BootCpuCount=%d "
          "Present=%u\n", __FUNCTION__, BootCpuCount, Present));
        //
        // The handling of QemuFwCfgItemSmpCpuCount, across CPU hotplug plus
        // platform reset (including S3), was corrected in QEMU commit
        // e3cadac073a9 ("pc: fix FW_CFG_NB_CPUS to account for -device added
        // CPUs", 2016-11-16), part of release v2.8.0.
        //
        BootCpuCount = (UINT16)Present;
      }

      mMaxCpuCount = Possible;
    }
  }

  DEBUG ((DEBUG_INFO, "%a: BootCpuCount=%d mMaxCpuCount=%u\n", __FUNCTION__,
    BootCpuCount, mMaxCpuCount));
  ASSERT (BootCpuCount <= mMaxCpuCount);

  PcdStatus = PcdSet32S (PcdCpuBootLogicalProcessorNumber, BootCpuCount);
  ASSERT_RETURN_ERROR (PcdStatus);
  PcdStatus = PcdSet32S (PcdCpuMaxLogicalProcessorNumber, mMaxCpuCount);
  ASSERT_RETURN_ERROR (PcdStatus);
}


/**
  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
InitializePlatform (
  IN       EFI_PEI_FILE_HANDLE  FileHandle,
  IN CONST EFI_PEI_SERVICES     **PeiServices
  )
{
  EFI_STATUS    Status;

  DEBUG ((DEBUG_INFO, "Platform PEIM Loaded\n"));

  DebugDumpCmos ();

  if (QemuFwCfgS3Enabled ()) {
    DEBUG ((DEBUG_INFO, "S3 support was detected on QEMU\n"));
    mS3Supported = TRUE;
    Status = PcdSetBoolS (PcdAcpiS3Enable, TRUE);
    ASSERT_EFI_ERROR (Status);
  }

  S3Verification ();
  BootModeInitialization ();
  AddressWidthInitialization ();

  //
  // Query Host Bridge DID
  //
  mHostBridgeDevId = PciRead16 (OVMF_HOSTBRIDGE_DID);

  MaxCpuCountInitialization ();

  if (FeaturePcdGet (PcdSmmSmramRequire)) {
    Q35BoardVerification ();
    Q35TsegMbytesInitialization ();
    Q35SmramAtDefaultSmbaseInitialization ();
  }

  PublishPeiMemory ();

  QemuUc32BaseInitialization ();

  InitializeRamRegions ();

  if (mBootMode != BOOT_ON_S3_RESUME) {
    if (!FeaturePcdGet (PcdSmmSmramRequire)) {
      ReserveEmuVariableNvStore ();
    }
    PeiFvInitialization ();
    MemTypeInfoInitialization ();
    MemMapInitialization ();
    NoexecDxeInitialization ();
  }

  InstallClearCacheCallback ();
  AmdSevInitialize ();
  MiscInitialization ();
  InstallFeatureControlCallback ();

  return EFI_SUCCESS;
}