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

Keir Fraser
2008-09-09T16:05:22Z

On 9/9/08 16:48, "Jeremy Fitzhardinge" <jeremy@goop.org> wrote:

> 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.

Oh, yes, our _PAGE_IO has the same meaning.

-- Keir