linux-kernel - Re: [PATCH] xen: core dom0 support

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Date:	Sun, 01 Mar 2009 16:46:48 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen: core dom0 support

Jeremy Fitzhardinge wrote:
>>
>> What do you define as "full PAT"?  If what you mean is that Xen lays
>> claims to the PAT MSR and only allows a certain mapping that's hardly
>> a problem... other than that it's not an exhaustible resource so I
>> guess I really don't understand what you're trying to say here.
> 
> It does not allow guests to set their own PAT MSRs.  It can't easily be
> multiplexed either, as all CPUs must have the same settings for their
> PAT MSRs.  I guess it could be handled by allowing domains to set their
> own virtual PAT MSRs, and then rewriting the ptes to convert from the
> guest PAT settings to Xen's, but I don't know if this is possible in
> general (and it poses some problems because the pte modifications would
> be guest-visible).
> 

It would make a lot more sense to simply specify a particular set of
mappings.  Since the only one anyone cares about that isn't in the
default set is WC anyway, it's easy to do.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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