Re: [RFC PATCH] net/mlx4: Get rid of page operation after dma_alloc_coherent

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On Tue, Dec 18, 2018 at 11:43:08AM -0700, Jason Gunthorpe wrote:
> So the problem here is that on some arches
> 
>  sg_set_buf(sg, dma_coherent_buf, size)
>  p = sg_virt(sg);
>  assert(p == dma_coherent_buf);

dma allocations purely return a virtual address, you must never
call virt_to_page or virt_to_phys on them, which sg_set_buf
will do.  On many architectures this will give your the wrong
result as the coherent DMA address is a vmap or ioremap address.



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