[PATCH stable-5.15] arm64: mm: Don't invalidate FROM_DEVICE buffers at start of DMA transfer

[PATCH stable-5.15] arm64: mm: Don't invalidate FROM_DEVICE buffers at start of DMA transfer

[Catalin Marinas]

From: Will Deacon <will@kernel.org>

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>
---
 arch/arm64/mm/cache.S | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
index 5051b3c1a4f1..79164e439036 100644
--- a/arch/arm64/mm/cache.S
+++ b/arch/arm64/mm/cache.S
@@ -231,8 +231,6 @@ SYM_FUNC_END_PI(__dma_flush_area)
  */
 SYM_FUNC_START_PI(__dma_map_area)
 	add	x1, x0, x1
-	cmp	w2, #DMA_FROM_DEVICE
-	b.eq	__dma_inv_area
 	b	__dma_clean_area
 SYM_FUNC_END_PI(__dma_map_area)
 

Re: [PATCH stable-5.15] arm64: mm: Don't invalidate FROM_DEVICE buffers at start of DMA transfer

[Greg Kroah-Hartman]

On Thu, Jun 23, 2022 at 04:44:12PM +0100, Catalin Marinas wrote:
> From: Will Deacon <will@kernel.org>
> 
> 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>
> ---
>  arch/arm64/mm/cache.S | 2 --
>  1 file changed, 2 deletions(-)

All now queued up, thanks.

greg k-h