The ArmPkg implementation of DmaLib uses double buffering to ensure that any attempt to perform non-coherent DMA on unaligned buffers cannot corrupt adjacent unrelated data which happens to share cachelines with the data we are exchanging with the device.
Such corruption can only occur on bus master read, in which case we have to invalidate the caches to ensure the CPU will see the data written to memory by the device. In the bus master write case, we can simply clean and invalidate at the same time, which may purge unrelated adjacent data from the caches, but will not corrupt its contents. Also, this double buffer does not necessarily have to be allocated from uncached memory: by the same reasoning, we can perform cache invalidation on an ordinary pool allocation as long as we take the same alignment constraints into account. So update our code accordingly: remove double buffering from the bus master read path, and switch to a pool allocation for the double buffer. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Ard Biesheuvel <[email protected]> --- ArmPkg/Library/ArmDmaLib/ArmDmaLib.c | 47 ++++++++++++-------- 1 file changed, 28 insertions(+), 19 deletions(-) diff --git a/ArmPkg/Library/ArmDmaLib/ArmDmaLib.c b/ArmPkg/Library/ArmDmaLib/ArmDmaLib.c index f4ee9e4c5ea2..61d70614bff0 100644 --- a/ArmPkg/Library/ArmDmaLib/ArmDmaLib.c +++ b/ArmPkg/Library/ArmDmaLib/ArmDmaLib.c @@ -80,6 +80,7 @@ DmaMap ( MAP_INFO_INSTANCE *Map; VOID *Buffer; EFI_GCD_MEMORY_SPACE_DESCRIPTOR GcdDescriptor; + UINTN AllocSize; if (HostAddress == NULL || NumberOfBytes == NULL || DeviceAddress == NULL || Mapping == NULL ) { return EFI_INVALID_PARAMETER; @@ -104,8 +105,9 @@ DmaMap ( return EFI_OUT_OF_RESOURCES; } - if ((((UINTN)HostAddress & (mCpu->DmaBufferAlignment - 1)) != 0) || - ((*NumberOfBytes & (mCpu->DmaBufferAlignment - 1)) != 0)) { + if (Operation != MapOperationBusMasterRead && + ((((UINTN)HostAddress & (mCpu->DmaBufferAlignment - 1)) != 0) || + ((*NumberOfBytes & (mCpu->DmaBufferAlignment - 1)) != 0))) { // Get the cacheability of the region Status = gDS->GetMemorySpaceDescriptor ((UINTN)HostAddress, &GcdDescriptor); @@ -129,21 +131,24 @@ DmaMap ( } // - // If the buffer does not fill entire cache lines we must double buffer into - // uncached memory. Device (PCI) address becomes uncached page. + // If the buffer does not fill entire cache lines we must double buffer + // into a suitably aligned allocation that allows us to invalidate the + // cache without running the risk of corrupting adjacent unrelated data. + // Note that pool allocations are guaranteed to be 8 byte aligned, so + // we only have to add (alignment - 8) worth of padding. // - Map->DoubleBuffer = TRUE; - Status = DmaAllocateBuffer (EfiBootServicesData, EFI_SIZE_TO_PAGES (*NumberOfBytes), &Buffer); - if (EFI_ERROR (Status)) { + Map->DoubleBuffer = TRUE; + AllocSize = ALIGN_VALUE (*NumberOfBytes, mCpu->DmaBufferAlignment) + + (mCpu->DmaBufferAlignment - 8); + Map->BufferAddress = AllocatePool (AllocSize); + if (Map->BufferAddress == NULL) { + Status = EFI_OUT_OF_RESOURCES; goto FreeMapInfo; } - if (Operation == MapOperationBusMasterRead) { - CopyMem (Buffer, HostAddress, *NumberOfBytes); - } - + Buffer = ALIGN_POINTER (Map->BufferAddress, mCpu->DmaBufferAlignment); *DeviceAddress = HostToDeviceAddress (ConvertToPhysicalAddress (Buffer)); - Map->BufferAddress = Buffer; + } else { Map->DoubleBuffer = FALSE; } @@ -207,6 +212,7 @@ DmaUnmap ( { MAP_INFO_INSTANCE *Map; EFI_STATUS Status; + VOID *Buffer; if (Mapping == NULL) { ASSERT (FALSE); @@ -217,17 +223,20 @@ DmaUnmap ( Status = EFI_SUCCESS; if (Map->DoubleBuffer) { - ASSERT (Map->Operation != MapOperationBusMasterCommonBuffer); + ASSERT (Map->Operation == MapOperationBusMasterWrite); - if (Map->Operation == MapOperationBusMasterCommonBuffer) { + if (Map->Operation != MapOperationBusMasterWrite) { Status = EFI_INVALID_PARAMETER; - } else if (Map->Operation == MapOperationBusMasterWrite) { - CopyMem ((VOID *)(UINTN)Map->HostAddress, Map->BufferAddress, - Map->NumberOfBytes); - } + } else { + Buffer = ALIGN_POINTER (Map->BufferAddress, mCpu->DmaBufferAlignment); + + mCpu->FlushDataCache (mCpu, (UINTN)Buffer, Map->NumberOfBytes, + EfiCpuFlushTypeInvalidate); - DmaFreeBuffer (EFI_SIZE_TO_PAGES (Map->NumberOfBytes), Map->BufferAddress); + CopyMem ((VOID *)(UINTN)Map->HostAddress, Buffer, Map->NumberOfBytes); + FreePool (Map->BufferAddress); + } } else { if (Map->Operation == MapOperationBusMasterWrite) { // -- 2.11.0 _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
