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Re: [Xen-devel] [PATCH] Allow PV superpages to work with live migration

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Allow PV superpages to work with live migration
From: Dave McCracken <dcm@xxxxxxxx>
Date: Tue, 18 May 2010 09:20:18 -0500
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen Developers List <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
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On Tuesday, May 18, 2010, Tim Deegan wrote:
> > PV superpages currently do not work with live migration.  They fall over
> > dead  when the shadow page table is enabled for dirty tracking.  The HVM
> > support for superpages in this code has been tested and found to work
> > just fine for PV superpages.  This patch modifies the test macro to
> > allow the code to work with PV superpages.
> It rather overshoots. :)  This enables PSE even for HVM guests which
> have explicitly disabled it.   I think you want
>     return (is_hvm_vcpu(v) ? (GUEST_PAGING_LEVELS != 2
>                               || !hvm_paging_enabled(v)
>                               || (v->arch.hvm_vcpu.guest_cr[4] &
> X86_CR4_PSE)) : opt_allow_hugepage);

I'm confused.  As far as I know, opt_allow_hugeage only affects PV guests.  All 
I did in the macro was add a test for it.  I didn't touch any of the HVM 
logic.  Are you saying the HVM logic is wrong or that opt_allow_hugepage 
affects HVM guests in some fashion?

Dave McCracken
Oracle Corp.

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