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RE: [PATCH 1/2] x86/mem_sharing: copy cpuid during vm forking
- To: "Cooper, Andrew" <andrew.cooper3@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: "Lengyel, Tamas" <tamas.lengyel@xxxxxxxxx>
- Date: Tue, 5 Jan 2021 15:50:39 +0000
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- Cc: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
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- Thread-topic: [PATCH 1/2] x86/mem_sharing: copy cpuid during vm forking
> -----Original Message-----
> From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Sent: Tuesday, January 5, 2021 6:05 AM
> To: Lengyel, Tamas <tamas.lengyel@xxxxxxxxx>; xen-
> devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>; Jan Beulich
> <jbeulich@xxxxxxxx>; George Dunlap <george.dunlap@xxxxxxxxxx>; Roger
> Pau Monné <roger.pau@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>
> Subject: Re: [PATCH 1/2] x86/mem_sharing: copy cpuid during vm forking
>
> On 04/01/2021 17:41, Tamas K Lengyel wrote:
> > Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
> > ---
> > xen/arch/x86/mm/mem_sharing.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/xen/arch/x86/mm/mem_sharing.c
> > b/xen/arch/x86/mm/mem_sharing.c index c428fd16ce..4a02c7d6f2
> 100644
> > --- a/xen/arch/x86/mm/mem_sharing.c
> > +++ b/xen/arch/x86/mm/mem_sharing.c
> > @@ -1764,6 +1764,7 @@ static int fork(struct domain *cd, struct domain
> > *d)
> >
> > domain_pause(d);
> > cd->max_pages = d->max_pages;
> > + memcpy(cd->arch.cpuid, d->arch.cpuid,
> > + sizeof(*d->arch.cpuid));
> > cd->parent = d;
> > }
> >
>
> You need to extend this to d->arch.msr and v->arch.msrs or someone is
> going to have a very subtle bug to debug in the future.
I need more information why v->arch.msrs would need to be copied manually. If
it's saved/reloaded by hvm_save/hvm_load then we are already covered. If not,
then why would we need to do that for forks but not for domain save/restore?
Tamas
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