[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
On 9/9/08 15:56, "Avi Kivity" <avi@xxxxxxxxxxxx> wrote: >> I'm not sure; I still don't really understand how _PAGE_SPECIAL gets >> used, other than being user-mode mapping only. But in principle, >> _PAGE_IOMAP could be set on both kernel and user mappings (if you direct >> map a device into a process address space), so I think they would >> conflict then? > > It's a "don't refcount me" flag, which is not sematically the same as > I/O, but may be close enough. 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. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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