[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC PATCH 0/2] xen/arm: fix "xen_add_mach_to_phys_entry: cannot add" problem
On Tue, 8 Jul 2014, David Vrabel wrote: > On 07/07/14 21:24, Stefano Stabellini wrote: > > Hi all, > > Xen support in Linux for ARM and ARM64 suffers from lack of support for > > multiple mfn to pfn mappings: whenever a frontend grants the same page > > multiple times to the backend, the mfn to pfn accounting in > > arch/arm/xen/p2m.c fails. The issue has become critical since v3.15, > > when xen-netfront/xen-netback switched from grant copies to grant > > mappings, therefore causing the issue to happen much more often. > > > > Fixing the mfn to pfn accounting in p2m.c is difficult and expensive, > > therefore we are looking for alternative solutions. One idea is avoiding > > mfn to pfn conversions altogether. The only code path that needs them is > > swiotlb-xen:unmap_page (and single_for_cpu and single_for_device). > > > > To avoid mfn to pfn conversions we rely on a second p2m mapping done by > > Xen, see the attached patch. In Linux we use it to perform the cache > > maintenance operations without mfns conversions. > > This will only work with PIPT caches (or certain types of VIPT that also > have alias detection). Do all the CPUs that Xen runs on have these type > of cache? Given that Xen only runs on v7 or newer I think we should be safe. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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