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

From: Keir Fraser
Date: Tue Sep 09 2008 - 12:05:22 EST

On 9/9/08 16:48, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> 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

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