Messages in this thread | | | Date | Mon, 9 Apr 2018 10:52:51 -0700 | From | Christoph Hellwig <> | Subject | Re: [PATCH] base: dma-mapping: Postpone cpu addr translation on mmap() |
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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?
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