On Fri, Mar 31, 2017 at 01:02:51PM +0200, Andrzej Hajda wrote:
> In case of DMA_ATTR_FORCE_CONTIGUOUS allocations vm_area->pages
> is invalid. __iommu_mmap_attrs and __iommu_get_sgtable should not
> use it and take advantage of contiguous nature of the allocation.
As I replied to your original patch, I think
dma_common_contiguous_remap() should be fixed not to leave a dangling
area->pages pointer.
> arch/arm64/mm/dma-mapping.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index f7b5401..41c7c36 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -703,6 +703,10 @@ static int __iommu_mmap_attrs(struct device *dev, struct
> vm_area_struct *vma,
> if (dma_mmap_from_coherent(dev, vma, cpu_addr, size, &ret))
> return ret;
>
> + if (attrs & DMA_ATTR_FORCE_CONTIGUOUS)
> + return vm_iomap_memory(vma,
> + page_to_phys(vmalloc_to_page(cpu_addr)), size);
I replied to Geert's patch on whether we actually need to call
dma_common_contiguous_remap() in __iommu_alloc_attrs() if the device is
coherent. We don't do this for the swiotlb allocation. If we are going
to change this, cpu_addr may or may not be in the vmalloc range and
vmalloc_to_page() would fail (I guess we could add an is_vmalloc_addr()
check).
Alternatively, just open-code dma_common_contiguous_remap() in
__iommu_alloc_attrs() to keep a valid area->pages around (I think Geert
already suggested this). AFAICT, arch/arm does this already in its own
__iommu_alloc_buffer().
Yet another option would be for iommu_dma_alloc() to understand
DMA_ATTR_FORCE_CONTIGUOUS and remove the arm64-specific handling.
> @@ -715,8 +719,19 @@ static int __iommu_get_sgtable(struct device *dev,
> struct sg_table *sgt,
> size_t size, unsigned long attrs)
> {
> unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> - struct vm_struct *area = find_vm_area(cpu_addr);
> + struct vm_struct *area;
> +
> + if (attrs & DMA_ATTR_FORCE_CONTIGUOUS) {
> + int ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
> +
> + if (!ret)
> + sg_set_page(sgt->sgl, vmalloc_to_page(cpu_addr),
> + PAGE_ALIGN(size), 0);
>
> + return ret;
> + }
> +
> + area = find_vm_area(cpu_addr);
As Russell already stated, this function needs a "fix" regardless of the
DMA_ATTR_FORCE_CONTIGUOUS as we may not have page structures
(*_from_coherent allocations). But I agree with you that
dma_get_sgtable() issues should be addressed separately (and I'm happy
to disable such API on arm64 until sorted).
--
Catalin
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