system76-edk2/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPei.c

/** @file

  Stateful and implicitly initialized fw_cfg library implementation.

  Copyright (C) 2013, Red Hat, Inc.
  Copyright (c) 2011 - 2013, Intel Corporation. All rights reserved.<BR>
  Copyright (c) 2017, Advanced Micro Devices. All rights reserved.<BR>

  SPDX-License-Identifier: BSD-2-Clause-Patent
**/

#include <PiPei.h>
#include <Library/BaseLib.h>
#include <Library/DebugLib.h>
#include <Library/HobLib.h>
#include <Library/IoLib.h>
#include <Library/PlatformInitLib.h>
#include <Library/QemuFwCfgLib.h>
#include <WorkArea.h>

#include "QemuFwCfgLibInternal.h"

/**
  Check if it is Tdx guest

  @retval    TRUE   It is Tdx guest
  @retval    FALSE  It is not Tdx guest
**/
STATIC
BOOLEAN
QemuFwCfgIsCcGuest (
  VOID
  )
{
  CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER  *CcWorkAreaHeader;

  CcWorkAreaHeader = (CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER *)FixedPcdGet32 (PcdOvmfWorkAreaBase);
  return (CcWorkAreaHeader != NULL && CcWorkAreaHeader->GuestType != CcGuestTypeNonEncrypted);
}

/**
  Returns a boolean indicating if the firmware configuration interface
  is available or not.

  This function may change fw_cfg state.

  @retval    TRUE   The interface is available
  @retval    FALSE  The interface is not available

**/
BOOLEAN
EFIAPI
QemuFwCfgIsAvailable (
  VOID
  )
{
  return InternalQemuFwCfgIsAvailable ();
}

STATIC
VOID
QemuFwCfgProbe (
  BOOLEAN  *Supported,
  BOOLEAN  *DmaSupported
  )
{
  UINT32   Signature;
  UINT32   Revision;
  BOOLEAN  CcGuest;

  // Use direct Io* calls for probing to avoid recursion.
  IoWrite16 (FW_CFG_IO_SELECTOR, (UINT16)QemuFwCfgItemSignature);
  IoReadFifo8 (FW_CFG_IO_DATA, sizeof Signature, &Signature);
  IoWrite16 (FW_CFG_IO_SELECTOR, (UINT16)QemuFwCfgItemInterfaceVersion);
  IoReadFifo8 (FW_CFG_IO_DATA, sizeof Revision, &Revision);
  CcGuest = QemuFwCfgIsCcGuest ();

  *Supported    = FALSE;
  *DmaSupported = FALSE;
  if ((Signature == SIGNATURE_32 ('Q', 'E', 'M', 'U')) && (Revision >= 1)) {
    *Supported = TRUE;
    if ((Revision & FW_CFG_F_DMA) && !CcGuest) {
      *DmaSupported = TRUE;
    }
  }

  DEBUG ((
    DEBUG_INFO,
    "%a: Supported %d, DMA %d\n",
    __func__,
    *Supported,
    *DmaSupported
    ));
}

STATIC
EFI_HOB_PLATFORM_INFO *
QemuFwCfgGetPlatformInfo (
  VOID
  )
{
  EFI_HOB_PLATFORM_INFO  *PlatformInfoHob;
  EFI_HOB_GUID_TYPE      *GuidHob;

  GuidHob = GetFirstGuidHob (&gUefiOvmfPkgPlatformInfoGuid);
  if (GuidHob == NULL) {
    return NULL;
  }

  PlatformInfoHob = (EFI_HOB_PLATFORM_INFO *)GET_GUID_HOB_DATA (GuidHob);

  if (!PlatformInfoHob->QemuFwCfgChecked) {
    QemuFwCfgProbe (
      &PlatformInfoHob->QemuFwCfgSupported,
      &PlatformInfoHob->QemuFwCfgDmaSupported
      );
    PlatformInfoHob->QemuFwCfgChecked = TRUE;
  }

  return PlatformInfoHob;
}

RETURN_STATUS
EFIAPI
QemuFwCfgInitialize (
  VOID
  )
{
  return RETURN_SUCCESS;
}

/**
  Returns a boolean indicating if the firmware configuration interface is
  available for library-internal purposes.

  This function never changes fw_cfg state.

  @retval    TRUE   The interface is available internally.
  @retval    FALSE  The interface is not available internally.
**/
BOOLEAN
InternalQemuFwCfgIsAvailable (
  VOID
  )
{
  EFI_HOB_PLATFORM_INFO  *PlatformInfoHob = QemuFwCfgGetPlatformInfo ();

  return PlatformInfoHob->QemuFwCfgSupported;
}

/**
  Returns a boolean indicating whether QEMU provides the DMA-like access method
  for fw_cfg.

  @retval    TRUE   The DMA-like access method is available.
  @retval    FALSE  The DMA-like access method is unavailable.
**/
BOOLEAN
InternalQemuFwCfgDmaIsAvailable (
  VOID
  )
{
  EFI_HOB_PLATFORM_INFO  *PlatformInfoHob = QemuFwCfgGetPlatformInfo ();

  return PlatformInfoHob->QemuFwCfgDmaSupported;
}

/**
  Transfer an array of bytes, or skip a number of bytes, using the DMA
  interface.

  @param[in]     Size     Size in bytes to transfer or skip.

  @param[in,out] Buffer   Buffer to read data into or write data from. Ignored,
                          and may be NULL, if Size is zero, or Control is
                          FW_CFG_DMA_CTL_SKIP.

  @param[in]     Control  One of the following:
                          FW_CFG_DMA_CTL_WRITE - write to fw_cfg from Buffer.
                          FW_CFG_DMA_CTL_READ  - read from fw_cfg into Buffer.
                          FW_CFG_DMA_CTL_SKIP  - skip bytes in fw_cfg.
**/
VOID
InternalQemuFwCfgDmaBytes (
  IN     UINT32  Size,
  IN OUT VOID    *Buffer OPTIONAL,
  IN     UINT32  Control
  )
{
  volatile FW_CFG_DMA_ACCESS  Access;
  UINT32                      AccessHigh, AccessLow;
  UINT32                      Status;

  ASSERT (
    Control == FW_CFG_DMA_CTL_WRITE || Control == FW_CFG_DMA_CTL_READ ||
    Control == FW_CFG_DMA_CTL_SKIP
    );

  if (Size == 0) {
    return;
  }

  //
  // TDX does not support DMA operations in PEI stage, we should
  // not have reached here.
  //
  ASSERT (!QemuFwCfgIsCcGuest ());

  Access.Control = SwapBytes32 (Control);
  Access.Length  = SwapBytes32 (Size);
  Access.Address = SwapBytes64 ((UINTN)Buffer);

  //
  // Delimit the transfer from (a) modifications to Access, (b) in case of a
  // write, from writes to Buffer by the caller.
  //
  MemoryFence ();

  //
  // Start the transfer.
  //
  AccessHigh = (UINT32)RShiftU64 ((UINTN)&Access, 32);
  AccessLow  = (UINT32)(UINTN)&Access;
  IoWrite32 (FW_CFG_IO_DMA_ADDRESS, SwapBytes32 (AccessHigh));
  IoWrite32 (FW_CFG_IO_DMA_ADDRESS + 4, SwapBytes32 (AccessLow));

  //
  // Don't look at Access.Control before starting the transfer.
  //
  MemoryFence ();

  //
  // Wait for the transfer to complete.
  //
  do {
    Status = SwapBytes32 (Access.Control);
    ASSERT ((Status & FW_CFG_DMA_CTL_ERROR) == 0);
  } while (Status != 0);

  //
  // After a read, the caller will want to use Buffer.
  //
  MemoryFence ();
}