linux-kernel - Re: [Xen-devel] Re: [PATCH 1 of 7] x86: add _PAGE

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Message-ID: <48C7F80C.6000807@goop.org>
Date:	Wed, 10 Sep 2008 09:38:36 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Avi Kivity <avi@...ranet.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Xen-devel] Re: [PATCH 1 of 7] x86: add _PAGE_IOMAP pte flag
 for IO	mappings

Avi Kivity wrote:
> Actually it's more of a "no struct page" flag, which implies no
> refcounting.

Hm, is that actually true enough to define it?  Could we rename it
something like _PAGE_NOSTRUCTPAGE or something a bit more specific than
"special"?

>   And not having a struct page should correspond well to a pte not
> requiring pfn->mfn conversion and being an I/O page.

But _PAGE_SPECIAL is only set in a few places.  It's not set in ioremap
mappings and so on.  Should it be?

There's also the hiccup that it gets set in a pte with pte_mkspecial() -
but at that point its too late because you've already constructed the
pte and done the pfn->mfn conversion.  _PAGE_IOMAP can only be set when
you initially construct the pte out of a frame number and a pgprot.

    J
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