[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [Xen-users] ARM: "xen_add_mach_to_phys_entry: cannot add ... already exists and panics"
On Fri, 4 Jul 2014, David Vrabel wrote: > On 04/07/14 15:12, Stefano Stabellini wrote: > > On Fri, 4 Jul 2014, David Vrabel wrote: > >> On 03/07/14 18:47, Stefano Stabellini wrote: > >>> > >>> At the moment I would like a way to disable grant mappings and go back > >>> to grant copies on demand. Maybe we could have a feature flag to change > >>> the behaviour of the network backend? > >> > >> You must fix the ARM code to handle this properly. > >> > >> blkback also uses grant maps and depending on the frontend blkback may > >> grant map the same machine frame multiple time. We have see frontends > >> that send such requests. > > > > Indeed, it must be fixed properly. The workaround of disabling grant > > mappings would be just to buy us some time to come up with the fix. > > It's an expensive workaround though. In terms of performances or in terms of code? If it's the performances you are worried about, we could enable the workaround just for arm and arm64. > >> I can't remember how the ARM code works. Where is the problematic m2p > >> lookup? > > > > arch/arm/xen/p2m.c > > > > > >> Perhaps this could be avoided for foreign frames? > > > > Unfortunately no. The whole point of p2m.c is to be able to translate > > foreign frames for dma operations. > > This is a p2m lookup though, which is fine, yes? Where, specifically is > a mfn_to_pfn() lookup needed for a foreign MFN. drivers/xen/swiotlb-xen.c:xen_unmap_single. xen_bus_to_phys is based on the value returned by mfn_to_pfn. > FWIW, On x86, mfn_to_pfn() on a foreign MFN will return an invalid value > (unless the gntdev device made the mapping and the m2p_override is used). Keep in mind that ARM domains are a bit like PVH without IOMMU. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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