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Re: [Xen-devel] Re: Xen's use of PAT and PV guests

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: Xen's use of PAT and PV guests
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 30 Mar 2010 11:25:32 -0700
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Dave McCracken <dave.mccracken@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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On 03/30/2010 10:59 AM, Keir Fraser wrote:
As it happens I think we do only support CPUs that have PAT. But you can
always check CPUID, just like running natively.

Yeah, I wasn't going to remove any of the tests, but I was wondering if the guest can always assume that it can set the pat flags in the pte. I guess that since Xen uses the same settings for the default pat (=no pat at all), then so long as the guest doesn't try to set _PAGE_PAT, then it doesn't matter.

Unfortunately hugetlbfs adds a wart, since it appears to end up going down to the make_pte/pte_val path, but we can't tell whether its a page with _PAGE_PSE or _PAGE_PAT set...


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