Okay, I'm about to merge the following patch for -rc, since refusing
to create a scattertable for non-page backed memory is the only valid
solution for that case. I'm intending to queue this for -rc this
evening.
8<====
ARM: dma-mapping: disallow dma_get_sgtable() for non-kernel managed memory
dma_get_sgtable() tries to create a scatterlist table containing valid
struct page pointers for the coherent memory allocation passed in to it.
However, memory can be declared via dma_declare_coherent_memory(), or
via other reservation schemes which means that coherent memory is not
guaranteed to be backed by struct pages. This means it is not possible
to create a valid scatterlist via this mechanism.
This patch adds detection of such memory, and refuses to create a
scatterlist table for such memory.
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
---
arch/arm/mm/dma-mapping.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 63eabb06f9f1..475811f5383a 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -935,13 +935,31 @@ static void arm_coherent_dma_free(struct device *dev, size_t size, void *cpu_add
__arm_dma_free(dev, size, cpu_addr, handle, attrs, true);
}
+/*
+ * The whole dma_get_sgtable() idea is fundamentally unsafe - it seems
+ * that the intention is to allow exporting memory allocated via the
+ * coherent DMA APIs through the dma_buf API, which only accepts a
+ * scattertable. This presents a couple of problems:
+ * 1. Not all memory allocated via the coherent DMA APIs is backed by
+ * a struct page
+ * 2. Passing coherent DMA memory into the streaming APIs is not allowed
+ * as we will try to flush the memory through a different alias to that
+ * actually being used (and the flushes are redundant.)
+ */
int arm_dma_get_sgtable(struct device *dev, struct sg_table *sgt,
void *cpu_addr, dma_addr_t handle, size_t size,
unsigned long attrs)
{
- struct page *page = pfn_to_page(dma_to_pfn(dev, handle));
+ unsigned long pfn = dma_to_pfn(dev, handle);
+ struct page *page;
int ret;
+ /* If the PFN is not valid, we do not have a struct page */
+ if (!pfn_valid(pfn))
+ return -ENXIO;
+
+ page = pfn_to_page(pfn);
+
ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
if (unlikely(ret))
return ret;
--
2.7.4
--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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