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Subject[PATCH 3.12 051/122] ARM: DMA: ensure that old section mappings are flushed from the TLB
From: Russell King <>

3.12-stable review patch. If anyone has any objections, please let me know.


commit 6b076991dca9817e75c37e2f0db6d52611ea42fa upstream.

When setting up the CMA region, we must ensure that the old section
mappings are flushed from the TLB before replacing them with page
tables, otherwise we can suffer from mismatched aliases if the CPU
speculatively prefetches from these mappings at an inopportune time.

A mismatched alias can occur when the TLB contains a section mapping,
but a subsequent prefetch causes it to load a page table mapping,
resulting in the possibility of the TLB containing two matching
mappings for the same virtual address region.

Acked-by: Will Deacon <>
Signed-off-by: Russell King <>
Cc: Hou Pengyang <>
Signed-off-by: Jiri Slaby <>
arch/arm/mm/dma-mapping.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index a2d0f91c5bd7..79cff8fdbaf3 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -429,12 +429,21 @@ void __init dma_contiguous_remap(void)

- * Clear previous low-memory mapping
+ * Clear previous low-memory mapping to ensure that the
+ * TLB does not see any conflicting entries, then flush
+ * the TLB of the old entries before creating new mappings.
+ *
+ * This ensures that any speculatively loaded TLB entries
+ * (even though they may be rare) can not cause any problems,
+ * and ensures that this code is architecturally compliant.
for (addr = __phys_to_virt(start); addr < __phys_to_virt(end);
addr += PMD_SIZE)

+ flush_tlb_kernel_range(__phys_to_virt(start),
+ __phys_to_virt(end));
iotable_init(&map, 1);

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