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

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Date:	Tue, 13 Feb 2007 17:36:23 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Dan Hecht <dhecht@...are.com>
CC:	Andi Kleen <ak@....de>, Andrew Morton <akpm@...l.org>,
	virtualization@...ts.osdl.org, xen-devel@...ts.xensource.com,
	Chris Wright <chrisw@...s-sol.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 05/21] Xen-paravirt: paravirt_ops: allocate a fixmap slot

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.

    J
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