On 17 August 2017 at 13:25, Ard Biesheuvel <[email protected]> wrote: > 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
*write* not read, apologies. > 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
