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

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On 06/22/11 18:10, Tim Deegan wrote:
> # HG changeset patch
> # User Tim Deegan<Tim.Deegan@xxxxxxxxxx>
> # Date 1308758648 -3600
> # Node ID b265371addbbc8a58c95a269fe3cd0fdc866aaa3
> # Parent  dcb8ae5e3eaf6516c889087dfb15efa41a1ac3e9
> Nested p2m: clarify logic in p2m_get_nestedp2m()
>
> This just makes the behaviour of this function a bit more explicit.  It
> may be that it also needs to be changed. :)
>
> Signed-off-by: Tim Deegan<Tim.Deegan@xxxxxxxxxx>
>
> 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);

The 'i'' variable is unused then. This fixes an endless loop of
nested page faults I observe with SMP l2 guests.

The nested page fault loop happens in conjunction with the change
in patch 4 in nestedhap_fix_p2m().

Christoph


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