Hello again,
On Tue, Apr 10, 2018 at 09:57:52AM +0200, jacopo mondi wrote:
> Hi Christoph,
>
> On Mon, Apr 09, 2018 at 10:52:51AM -0700, Christoph Hellwig wrote:
> > 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.
>
> I see.. this patch thus just postpones the problem...
>
> >
> > > #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?
>
> Sure, it's better... Should I send a v2 or considering your above
> comment this patch is just a mitigation and should be ditched in
> favour of a proper solution (which requires a much more considerable amount
> of work though)?
Don't want to be insistent, but I didn't get from your reply if a v2
is welcome or not :)
Thanks
j
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