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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Will Deacon <will@kernel.org>
Date: Fri, 10 Jun 2022 16:12:27 +0100
Subject: [PATCH] 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>
---
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 0ea6cc25dc66356de86d262cc3d48bb993ec3cd0..21c907987080f60d4b25ef70f438332a6c1c24cc 100644
--- a/arch/arm64/mm/cache.S
+++ b/arch/arm64/mm/cache.S
@@ -218,8 +218,6 @@ SYM_FUNC_ALIAS(__dma_flush_area, __pi___dma_flush_area)
*/
SYM_FUNC_START(__pi___dma_map_area)
add x1, x0, x1
- cmp w2, #DMA_FROM_DEVICE
- b.eq __pi_dcache_inval_poc
b __pi_dcache_clean_poc
SYM_FUNC_END(__pi___dma_map_area)
SYM_FUNC_ALIAS(__dma_map_area, __pi___dma_map_area)
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