Re: [Xen-devel] [PATCH v7 1/7] x86/p2m: Allow p2m_get_page_from_gfn to return shared entries

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Mon, Feb 3, 2020 at 9:24 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 03.02.2020 17:12, Tamas K Lengyel wrote:
> > The owner domain of shared pages is dom_cow, use that for get_page
> > otherwise the function fails to return the correct page under some
> > situations. The check if dom_cow should be used was only performed in
> > a subset of use-cases. Fixing the error and simplifying the existing check
> > since we can't have any shared entries with dom_cow being NULL.
>
> Better, thanks.
>
> > Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
> > ---
> > v7: update commit message
> > ---
> >  xen/arch/x86/mm/p2m.c | 14 ++++++++------
> >  1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> > index def13f657b..007fef720d 100644
> > --- a/xen/arch/x86/mm/p2m.c
> > +++ b/xen/arch/x86/mm/p2m.c
> > @@ -575,11 +575,12 @@ struct page_info *p2m_get_page_from_gfn(
> >                  if ( fdom == NULL )
> >                      page = NULL;
> >              }
> > -            else if ( !get_page(page, p2m->domain) &&
> > -                      /* Page could be shared */
> > -                      (!dom_cow || !p2m_is_shared(*t) ||
> > -                       !get_page(page, dom_cow)) )
> > -                page = NULL;
> > +            else
> > +            {
> > +                struct domain *d = !p2m_is_shared(*t) ? p2m->domain : 
> > dom_cow;
> > +                if ( !get_page(page, d) )
>
> There's still a blank line missing between these two lines and ...
>
> > +                    page = NULL;
> > +            }
> >          }
> >          p2m_read_unlock(p2m);
> >
> > @@ -595,8 +596,9 @@ struct page_info *p2m_get_page_from_gfn(
> >      mfn = get_gfn_type_access(p2m, gfn_x(gfn), t, a, q, NULL);
> >      if ( p2m_is_ram(*t) && mfn_valid(mfn) )
> >      {
> > +        struct domain *d = !p2m_is_shared(*t) ? p2m->domain : dom_cow;
> >          page = mfn_to_page(mfn);
>
> ... similarly between these two. As indicated before, with them
> added
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> despite me still thinking that the title suggests more of a
> problem than there really was. (Of course adding the missing
> blank lines ought to be easy enough while committing.)

Thanks, I did forgot to add those extra lines. To me this looks fine
as-is so it just doesn't come to mind naturally.

Tamas

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