[PATCH/RFC 6/7] dma-direct: do not skip cache maintenance for highmem pages in no-mapping allocations

[Marek Szyprowski <m.szyprowski@samsung.com>]

dma_direct_alloc_no_mapping() calls arch_dma_prep_coherent() only for
lowmem pages. The check was added when the DMA_ATTR_NO_KERNEL_MAPPING
handling was moved to dma-direct, because some implementations of the
hook used page_address() and could not handle highmem pages.

As a result, a buffer backed by a highmem CMA page is handed to the
device without removing the dirty cache lines covering it, which may
still be present from the previous user of the page. These lines can be
evicted later and corrupt data written by a non-coherent device.

All implementations of arch_dma_prep_coherent() now handle highmem
pages, and the hook is documented to do so; dma_direct_alloc() already
calls it on highmem pages in its remap path. Drop the check so that
highmem pages get the same cache maintenance as lowmem pages.

Fixes: d98849aff879 ("dma-direct: handle DMA_ATTR_NO_KERNEL_MAPPING in common code")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
 kernel/dma/direct.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 25e9a86835fd..fea0dd36dd25 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -207,8 +207,7 @@ static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size,
 		return NULL;
 
 	/* remove any dirty cache lines on the kernel alias */
-	if (!PageHighMem(page))
-		arch_dma_prep_coherent(page, size);
+	arch_dma_prep_coherent(page, size);
 	/*
 	 * return the page pointer as the opaque cookie.
 	 * Never used for unencrypted allocation
-- 
2.43.0