linux-kernel - Re: [PATCH] x86: fix PSE pagetable construction

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Message-ID: <m1odl9gfz9.fsf@ebiederm.dsl.xmission.com>
Date:	Sat, 28 Apr 2007 00:39:22 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andi Kleen <ak@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86: fix PSE pagetable construction

Jeremy Fitzhardinge <jeremy@...p.org> writes:

> I don't have any particularly bright ideas, but there is the other idea
> I mentioned.  I could pre-initialize the pagetable with the Xen
> template, but use unconditional calls to set_pte in pagetable_init. 
> However, the init-time xen_set_pte simply refuse to set _PAGE_WRITE on a
> pte which isn't already writable, thereby protecting the RO state of the
> pagetable pages.  Once pagetable construction has finished, it would
> switch to the real xen_set_pte, which operates as normal.
>
> This has the downside of making init-time xen_set_pte a little strange,
> but it does have the advantage of making the Xen constraints solely the
> responsibility of the Xen code, and it is mitigated by the fact that it
> is only in effect during pagetable_init.
>
> Would that work for everyone?

For a short term solution it sounds reasonable.

Eric
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