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OvmfPkg/QemuFwCfgLib: Use BusMasterCommonBuffer to map FW_CFG_DMA_ACCESS

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Commit 09719a01b1 (OvmfPkg/QemuFwCfgLib: Implement SEV internal function
for Dxe phase) uses IOMMU protocol to allocate and free FW_CFG_DMA_ACCESS
buffer when SEV is active. During initial commits we made assumption that
IOMMU.AllocateBuffer() will provide PlainTextAddress (i.e C-bit cleared).
This assumption was wrong, the AllocateBuffer() protocol member is not
expected to produce a buffer that is immediatly usable, and client is
required to call Map() uncondtionally with BusMasterCommonBuffer[64] to
get a mapping which is accessable by both host and device.

The patch refactors code a bit and add the support to Map()
FW_CFG_DMA_ACCESS buffer using BusMasterCommonBuffer operation after
allocation and Unamp() before free.

The complete discussion about this and recommendation from Laszlo can be
found here [1]

[1] https://lists.01.org/pipermail/edk2-devel/2017-July/012652.html

Suggested-by: Laszlo Ersek <lersek@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
[lersek@redhat.com: convert pointers to UINTN before converting to UINT64]
[lersek@redhat.com: fix argument indentation in multi-line function call]
[lersek@redhat.com: explicitly compare pointers to NULL]
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
This commit is contained in:
Brijesh Singh
2017-08-02 18:12:48 -04:00
committed by Laszlo Ersek
parent d0c9afea42
commit f6c909ae5d
5 changed files with 373 additions and 298 deletions
Download Patch File Download Diff File Expand all files Collapse all files

130
OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c
View File

@@ -45,136 +45,6 @@ QemuFwCfgSelectItem (
IoWrite16 (FW_CFG_IO_SELECTOR, (UINT16)(UINTN) QemuFwCfgItem);
}
/**
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 LocalAccess;
volatile FW_CFG_DMA_ACCESS *Access;
UINT32 AccessHigh, AccessLow;
UINT32 Status;
UINT32 NumPages;
VOID *DmaBuffer, *BounceBuffer;
ASSERT (Control == FW_CFG_DMA_CTL_WRITE || Control == FW_CFG_DMA_CTL_READ ||
Control == FW_CFG_DMA_CTL_SKIP);
if (Size == 0) {
return;
}
//
// set NumPages to suppress incorrect compiler/analyzer warnings
//
NumPages = 0;
//
// When SEV is enabled then allocate DMA bounce buffer
//
if (InternalQemuFwCfgSevIsEnabled ()) {
UINTN TotalSize;
TotalSize = sizeof (*Access);
//
// Skip operation does not need buffer
//
if (Control != FW_CFG_DMA_CTL_SKIP) {
TotalSize += Size;
}
//
// Allocate SEV DMA buffer
//
NumPages = (UINT32)EFI_SIZE_TO_PAGES (TotalSize);
InternalQemuFwCfgSevDmaAllocateBuffer (&BounceBuffer, NumPages);
Access = BounceBuffer;
DmaBuffer = (UINT8*)BounceBuffer + sizeof (*Access);
//
// Decrypt data from encrypted guest buffer into DMA buffer
//
if (Control == FW_CFG_DMA_CTL_WRITE) {
CopyMem (DmaBuffer, Buffer, Size);
}
} else {
Access = &LocalAccess;
DmaBuffer = Buffer;
BounceBuffer = NULL;
}
Access->Control = SwapBytes32 (Control);
Access->Length = SwapBytes32 (Size);
Access->Address = SwapBytes64 ((UINTN)DmaBuffer);
//
// 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 ();
//
// If Bounce buffer was allocated then copy the data into guest buffer and
// free the bounce buffer
//
if (BounceBuffer != NULL) {
//
// Encrypt the data from DMA buffer into guest buffer
//
if (Control == FW_CFG_DMA_CTL_READ) {
CopyMem (Buffer, DmaBuffer, Size);
}
InternalQemuFwCfgSevDmaFreeBuffer (BounceBuffer, NumPages);
}
}
/**
Reads firmware configuration bytes into a buffer