On Mon, 8 Feb 2016, Ian Campbell wrote:
> Currently xen_dma_map_page concludes that DMA to anything other than
> the head page of a compound page must be foreign, since the PFN of the
> page is that of the head.
>
> Fix the check to instead consider the whole of a compound page to be
> local if the PFN of the head passes the 1:1 check.
>
> We can never see a compound page which is a mixture of foreign and
> local sub-pages.
>
> The comment already correctly described the intention, but fixup the
> spelling and some grammar.
>
> This fixes the various SSH protocol errors which we have been seeing
> on the cubietrucks in our automated test infrastructure.
>
> This has been broken since "xen/arm: use hypercall to flush caches in
> map_page" (3567258d281b), which was in v3.19-rc1.
checkpatch.pl reports a small style issue with this statement.
> NB arch/arm64/.../xen/page-coherent.h also includes this file.
>
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx # v3.19+
> ---
> arch/arm/include/asm/xen/page-coherent.h | 19 ++++++++++++-------
> 1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm/include/asm/xen/page-coherent.h b/arch/arm/include/asm/xen/page-coherent.h
> index 0375c8c..5653739 100644
> --- a/arch/arm/include/asm/xen/page-coherent.h
> +++ b/arch/arm/include/asm/xen/page-coherent.h
> @@ -35,14 +35,19 @@ static inline void xen_dma_map_page(struct device *hwdev, struct page *page,
> dma_addr_t dev_addr, unsigned long offset, size_t size,
> enum dma_data_direction dir, struct dma_attrs *attrs)
> {
> - bool local = XEN_PFN_DOWN(dev_addr) == page_to_xen_pfn(page);
> + unsigned long page_pfn = page_to_xen_pfn(page);
> + unsigned long dev_pfn = XEN_PFN_DOWN(dev_addr);
> + unsigned long compound_pages = 1<<compound_order(page);
To take care of 64k pages, this needs to be:
unsigned long compound_pages = (1<<compound_order(page)) * XEN_PFN_PER_PAGE;
> + bool local = page_pfn <= dev_pfn && dev_pfn - page_pfn < compound_pages;
Since you are at it, it might be worth adding brackets.
> /*
> - * Dom0 is mapped 1:1, while the Linux page can be spanned accross
> - * multiple Xen page, it's not possible to have a mix of local and
> - * foreign Xen page. So if the first xen_pfn == mfn the page is local
> - * otherwise it's a foreign page grant-mapped in dom0. If the page is
> - * local we can safely call the native dma_ops function, otherwise we
> - * call the xen specific function.
> + * Dom0 is mapped 1:1, while the Linux page can span across
> + * multiple Xen pages, it's not possible for it to contain a
> + * mix of local and foreign Xen pages. So if the first xen_pfn
> + * == mfn the page is local otherwise it's a foreign page
> + * grant-mapped in dom0. If the page is local we can safely
> + * call the native dma_ops function, otherwise we call the xen
> + * specific function.
> */
> if (local)
> __generic_dma_ops(hwdev)->map_page(hwdev, page, offset, size, dir, attrs);
> --
> 2.1.4
>
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