On Mon, Apr 09, 2018 at 06:59:08PM +0200, Jacopo Mondi wrote:
> I'm still a bit puzzled on what happens if dma_mmap_from_dev_coherent() fails.
> Does a dma_mmap_from_dev_coherent() failure guarantee anyhow that the
> successive virt_to_page() isn't problematic as it is today?
> Or is it the
> if (off < count && user_count <= (count - off))
> check that makes the translation safe?
It doesn't. I think one major issue is that we should not simply fall
to dma_common_mmap if no method is required, but need every instance of
dma_map_ops to explicitly opt into an mmap method that is known to work.
> #ifndef CONFIG_ARCH_NO_COHERENT_DMA_MMAP
> unsigned long user_count = vma_pages(vma);
> unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> - unsigned long pfn = page_to_pfn(virt_to_page(cpu_addr));
> unsigned long off = vma->vm_pgoff;
> + unsigned long pfn;
>
> vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>
> @@ -235,6 +235,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
> return ret;
>
> if (off < count && user_count <= (count - off)) {
> + pfn = page_to_pfn(virt_to_page(cpu_addr));
> ret = remap_pfn_range(vma, vma->vm_start,
> pfn + off,
> user_count << PAGE_SHIFT,
Why not:
ret = remap_pfn_range(vma, vma->vm_start,
page_to_pfn(virt_to_page(cpu_addr)) + off,
and save the temp variable?
