Messages in this thread | | | Date | Thu, 06 Jan 2011 20:17:38 +0000 | Subject | Re: [PATCH 6/8] xen/debug: WARN_ON when 1-1 but no _PAGE_IOMAP flag set. | From | Keir Fraser <> |
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On 06/01/2011 19:50, "Stefano Stabellini" <stefano.stabellini@eu.citrix.com> wrote:
>> Perhaps this ties in with the m2p overlay which Stefano+Jeremy have been >> working on to deal with granted foreign pages? I/O pages are a bit like >> foreign memory (if you squint enough)... > > In theory the m2p overlay could be used for this purpose but in practice > the current m2p overlay API needs a struct page, also it might end up > stressing the hashtable too much. > > Besides I think Konrad's solution might be simpler: if the m2p returns > one of the two special values we just return mfn from pte_mfn_to_pfn. > > Keir, could you confirm that the m2p entries of DOM_IO pages are always > 0xffffff or 0x55555?
Always 0x55...55 (for m2p entries that exist), else page fault on access to the non-existent m2p entry (m2p entries only guaranteed to exist for ram). Perhaps the 0xff...ff values come from Linux's own fixup code handling a faulting read access of the m2p array? If so you could return 0x55...55 instead and avoid checking for 0xff...ff. I really don't know how you could get 0xff...ff for non-RAM pages from Xen itself.
-- Keir
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