arm64: mm: Don't invalidate FROM_DEVICE buffers at start of DMA transfer

commit 6ada6b38bf6113418b1ee1857e9c21bba96a38db upstream.

Invalidating the buffer memory in arch_sync_dma_for_device() for
FROM_DEVICE transfers

When using the streaming DMA API to map a buffer prior to inbound
non-coherent DMA (i.e. DMA_FROM_DEVICE), we invalidate any dirty CPU
cachelines so that they will not be written back during the transfer and
corrupt the buffer contents written by the DMA. This, however, poses two
potential problems:

  (1) If the DMA transfer does not write to every byte in the buffer,
      then the unwritten bytes will contain stale data once the transfer
      has completed.

  (2) If the buffer has a virtual alias in userspace, then stale data
      may be visible via this alias during the period between performing
      the cache invalidation and the DMA writes landing in memory.

Address both of these issues by cleaning (aka writing-back) the dirty
lines in arch_sync_dma_for_device(DMA_FROM_DEVICE) instead of discarding
them using invalidation.

Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220606152150.GA31568@willie-the-truck
Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220610151228.4562-2-will@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
index db767b072601e36fddb8ee7991d801d6f1f2f6d6..7b054c67acd816da32f400787c6fc71ddb887b62 100644 (file)
--- a/arch/arm64/mm/cache.S
+++ b/arch/arm64/mm/cache.S
@@ -228,8 +228,6 @@ ENDPIPROC(__dma_flush_area)
  *     - dir   - DMA direction
  */
 ENTRY(__dma_map_area)
-       cmp     w2, #DMA_FROM_DEVICE
-       b.eq    __dma_inv_area
        b       __dma_clean_area
 ENDPIPROC(__dma_map_area)