RE: [PATCH 1/2] x86/mem_sharing: copy cpuid during vm forking

["Lengyel, Tamas" <tamas.lengyel@intel.com>]

> -----Original Message-----
> From: Andrew Cooper <andrew.cooper3@citrix.com>
> Sent: Tuesday, January 5, 2021 6:05 AM
> To: Lengyel, Tamas <tamas.lengyel@intel.com>; xen-
> devel@lists.xenproject.org
> Cc: Tamas K Lengyel <tamas@tklengyel.com>; Jan Beulich
> <jbeulich@suse.com>; George Dunlap <george.dunlap@citrix.com>; Roger
> Pau Monné <roger.pau@citrix.com>; Wei Liu <wl@xen.org>
> 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@intel.com>
> > ---
> >  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