Re: [Xen-devel] [PATCH v2 18/20] xen/mem_access: Use __get_gfn_type_access in set_mem_access

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, Dec 19, 2019 at 12:59 AM Alexandru Stefan ISAILA
<aisaila@xxxxxxxxxxxxxxx> wrote:
>
>
>
> On 18.12.2019 21:40, Tamas K Lengyel wrote:
> > Use __get_gfn_type_access instead of p2m->get_entry to trigger page-forking
> > when the mem_access permission is being set on a page that has not yet been
> > copied over from the parent.
> >
> > Signed-off-by: Tamas K Lengyel <tamas.lengyel@intel.comReviewed-by: 
> > Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
>
> > ---
> >   xen/arch/x86/mm/mem_access.c | 5 ++---
> >   1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
> > index 320b9fe621..9caf08a5b2 100644
> > --- a/xen/arch/x86/mm/mem_access.c
> > +++ b/xen/arch/x86/mm/mem_access.c
> > @@ -303,11 +303,10 @@ static int set_mem_access(struct domain *d, struct 
> > p2m_domain *p2m,
> >       ASSERT(!ap2m);
> >   #endif
> >       {
> > -        mfn_t mfn;
> >           p2m_access_t _a;
> >           p2m_type_t t;
> > -
> > -        mfn = p2m->get_entry(p2m, gfn, &t, &_a, 0, NULL, NULL);
> > +        mfn_t mfn = __get_gfn_type_access(p2m, gfn_x(gfn), &t, &_a,
> > +                                          P2M_ALLOC, NULL, false);
>
> Don't you want p2m_query_t to be 0 as it was in the p2m->get_entry() call ?

No, the entire point of the patch is to have the P2M_ALLOC query flag
set. That triggers the fork's p2m population.

Tamas

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