| Message ID | 1454938450-26282-1-git-send-email-ian.campbell@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@citrix.com> > Cc: xen-devel@lists.xenproject.org > Cc: linux-arm-kernel@lists.infradead.org > Cc: stable@vger.kernel.org # 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 >
On Mon, 2016-02-08 at 15:46 +0000, Stefano Stabellini wrote: > 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. Damn, I added that para after I'd already run checkpatch. > [...] > > To take care of 64k pages, this needs to be: > {...] > Since you are at it, it might be worth adding brackets. Will do on both counts. v2 on its way. Ian.
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); + bool local = page_pfn <= dev_pfn && dev_pfn - page_pfn < compound_pages; + /* - * 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);
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. NB arch/arm64/.../xen/page-coherent.h also includes this file. Signed-off-by: Ian Campbell <ian.campbell@citrix.com> Cc: xen-devel@lists.xenproject.org Cc: linux-arm-kernel@lists.infradead.org Cc: stable@vger.kernel.org # v3.19+ --- arch/arm/include/asm/xen/page-coherent.h | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-)