Re: [Xen-devel] Re: [PATCH 1 of 7] x86: add _PAGE_IOMAP pte flag for IO mappings

Avi Kivity
2008-09-10T09:55:36Z

Avi Kivity 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.

Actually it's more of a "no struct page" flag, which implies no
refcounting. And not having a struct page should correspond well to a
pte not requiring pfn->mfn conversion and being an I/O page.

--
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