Re: [Xen-devel] [PATCH] x86/mm: relax the check in get_pg_owner

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Mar 24, 2017 at 02:12:47AM -0600, Jan Beulich wrote:
> >>> On 23.03.17 at 19:08, <wei.liu2@xxxxxxxxxx> wrote:
> > PVH guest is actually an translated guest. It should be able to
> > manipulate page table for other domains when acting as Dom0.
> 
> The same was true for PVHv1, so I'm afraid there's a little more to
> this.
> 
> > --- a/xen/arch/x86/mm.c
> > +++ b/xen/arch/x86/mm.c
> > @@ -3041,12 +3041,6 @@ static struct domain *get_pg_owner(domid_t domid)
> >          goto out;
> >      }
> >  
> > -    if ( unlikely(paging_mode_translate(curr)) )
> > -    {
> > -        MEM_LOG("Cannot mix foreign mappings with translated domains");
> > -        goto out;
> > -    }
> 
> Prior to Roger's recent removal of PVHv1 code this was
> 
>     if ( !is_pvh_domain(curr) && unlikely(paging_mode_translate(curr)) )
> 
> Instead of removing the left side, I think it should have been
> converted to !is_hvm_domain() (or is_pv_domain()).
> 

DYM:

    if ( !is_hvm_domain(curr) && unlikely(paging_mode_translate(curr)) )

?

Here is something I'm not entirely sure of: is autotranslated PV guest
still a thing? I thought Andrew removed it already?

> Protection against this being used on other than PV domains
> as target luckily looks to be there:
> - mmuext and mmu_update already have respective (albeit
>   somewhat inconsistent) checks,
> - do_update_va_mapping_otherdomain() is not wired up for
>   HVM.

Yes. That's right.

Wei.

> 
> Jan
> 

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