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

commit c50f11c6196f45c92ca48b16a5071615d4ae0572 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 2d881f34dd9d54017c7565cc5749d88084ab4235..7b8158ae36ecc6eb0c078ec1d7822ac14118e9df 100644 (file)
--- a/arch/arm64/mm/cache.S
+++ b/arch/arm64/mm/cache.S
@@ -228,8 +228,6 @@ SYM_FUNC_END_PI(__dma_flush_area)
  *     - dir   - DMA direction
  */
 SYM_FUNC_START_PI(__dma_map_area)
-       cmp     w2, #DMA_FROM_DEVICE
-       b.eq    __dma_inv_area
        b       __dma_clean_area
 SYM_FUNC_END_PI(__dma_map_area)