[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Re: [PATCH 1 of 7] x86: add _PAGE_IOMAP pte flag for IO mappings
Keir Fraser wrote: > That's basically what our _PAGE_IO flag (in our old Linux patchset) means. > We use it to cause pte_pfn() to return an invalid pfn and hence avoid > reference counting that way. Since kernel mappings are never reference > counted (I think?) perhaps we could use _PAGE_SPECIAL even if it is > restricted to use on user mappings. Well, _PAGE_IOMAP's most important semantic from Xen's perspective is that the frame number is considered to already be an MFN and so isn't converted. It may be that _PAGE_SPECIAL is also useful for its "no refcount" properties, but we could set both in that case. At present we can't set _PAGE_SPECIAL on kernel mappings because we assume its usermode only, and its shared with _PAGE_CPA_TEST which is kernel-only. Most _PAGE_IOMAP mappings are in kernel space, but I wouldn't discount user mappings if we end up allowing direct access to passthrough devices. J _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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