linux-kernel - Re: [Xen-devel] Re: [patch 05/21] Xen-paravirt: paravirt

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Date:	Wed, 14 Feb 2007 10:15:04 +0100
From:	Andi Kleen <ak@....de>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	virtualization@...ts.osdl.org, xen-devel@...ts.xensource.com,
	Andrew Morton <akpm@...l.org>,
	Chris Wright <chrisw@...s-sol.org>,
	linux-kernel@...r.kernel.org, Dan Hecht <dhecht@...are.com>
Subject: Re: [Xen-devel] Re: [patch 05/21] Xen-paravirt: paravirt_ops: allocate a fixmap slot

On Wed, Feb 14, 2007 at 08:37:26AM +0000, Jan Beulich wrote:
> >>> Jeremy Fitzhardinge <jeremy@...p.org> 14.02.07 02:36 >>>
> >Dan Hecht wrote:
> >> Why doesn't Xen allocate the shared_info page from the pseudo-physical
> >> space?  Doesn't it already have to steal pages from the
> >> pseudo-physical space for e.g. initial page tables, console, etc?  Why
> >> not do the same for shared_info, and then you don't need a reserve the
> >> fixmap slot.
> >
> >Unlike the pagetable pages or the console page, the shared info page
> >doesn't have a pseudo-physical address, so in order to map it we need to
> >directly construct a pte containing the mfn for that page.  Inserting
> >this mapping into the fixmap space seems like the easiest way to do
> >this.  It's not like a fixmap slot costs anything.
> 
> Otoh there are many fixmap slots not used under Xen, perhaps it would
> be possible to use one of those... One slot certainly doesn't cost a lot,

I don't have a problem with reserving one page for this.

-Andi
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