[Xen-devel] Re: [PATCH 3 of 4] Nested p2m: clarify logic in p2m_get_nestedp2m()

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

At 15:25 +0100 on 24 Jun (1308929140), Christoph Egger wrote:
> > diff -r dcb8ae5e3eaf -r b265371addbb xen/arch/x86/mm/p2m.c
> > --- a/xen/arch/x86/mm/p2m.c Wed Jun 22 17:04:08 2011 +0100
> > +++ b/xen/arch/x86/mm/p2m.c Wed Jun 22 17:04:08 2011 +0100
> > @@ -1131,11 +1131,9 @@ p2m_get_nestedp2m(struct vcpu *v, uint64
> >
> >       d = v->domain;
> >       nestedp2m_lock(d);
> > -    for (i = 0; i<  MAX_NESTEDP2M; i++) {
> > -        p2m = d->arch.nested_p2m[i];
> > -        if ((p2m->cr3 != cr3&&  p2m->cr3 != CR3_EADDR) || (p2m != 
> > nv->nv_p2m))
> > -            continue;
> > -
> > +    p2m = nv->nv_p2m;
> > +    if ( p2m&&  (p2m->cr3 == cr3 || p2m->cr3 == CR3_EADDR) )
> > +    {
> >           nv->nv_flushp2m = 0;
> >           p2m_getlru_nestedp2m(d, p2m);
> >           nv->nv_p2m = p2m;
> >
> 
> 
> Ok, thanks.
> 
> In p2m_get_nestedp2m() replace this code hunk
> 
>      for (i = 0; i < MAX_NESTEDP2M; i++) {
>          p2m = p2m_getlru_nestedp2m(d, NULL);
>          p2m_flush_locked(p2m);
>      }
> 
> with
> 
>      p2m = p2m_getlru_nestedp2m(d, NULL);
>      p2m_flush_locked(p2m);

That seems like an improvement.  I'll put it into my queue.  

More generally, I think that you need to figure out exactly what
behaviour you want from this function.  For example in the current code
there's no way that two vcpus with the same ncr3 value can share a
nested-p2m.  Is that deliberate?

Cheers,

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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