Re: [V7 PATCH 3/7] pvh dom0: implement XENMEM_add_to_physmap_range for x86

[Mukesh Rathor <mukesh.rathor@oracle.com>]

On Tue, 17 Dec 2013 13:07:22 +0000
"Jan Beulich" <JBeulich@suse.com> wrote:

> >>> On 17.12.13 at 03:38, Mukesh Rathor <mukesh.rathor@oracle.com>
> >>> wrote:
> > --- a/xen/arch/x86/mm.c
> > +++ b/xen/arch/x86/mm.c
> > @@ -4675,6 +4675,39 @@ static int xenmem_add_to_physmap(struct
> > domain *d, return xenmem_add_to_physmap_once(d, xatp);
> >  }
> >  
> > +static int xenmem_add_to_physmap_range(struct domain *d,
> > +                                       struct
> > xen_add_to_physmap_range *xatpr) +{
> > +    /* Process entries in reverse order to allow continuations */
> > +    while ( xatpr->size > 0 )
> > +    {
> > +        int rc;
> > +        xen_ulong_t idx;
> > +        xen_pfn_t gpfn;
> > +        struct xen_add_to_physmap xatp;
> > +
> > +        if ( copy_from_guest_offset(&idx, xatpr->idxs,
> > xatpr->size-1, 1)  ||
> > +             copy_from_guest_offset(&gpfn, xatpr->gpfns,
> > xatpr->size-1, 1) )
> > +            return -EFAULT;
> > +
> > +        xatp.space = xatpr->space;
> > +        xatp.idx = idx;
> > +        xatp.gpfn = gpfn;
> > +        rc = xenmem_add_to_physmap_once(d, &xatp);
> > +
> > +        if ( copy_to_guest_offset(xatpr->errs, xatpr->size-1, &rc,
> > 1) )
> > +            return -EFAULT;
> > +
> > +        xatpr->size--;
> > +
> > +        /* Check for continuation if it's not the last interation
> > */
> > +        if ( xatpr->size > 0 && hypercall_preempt_check() )
> > +            return -EAGAIN;
> > +    }
> > +
> > +    return 0;
> > +}
> 
> Now that I started looking into creating the compat wrapper for this,
> I realize that processing this request backwards is wrong: The effect
> of the entire hypercall can end up being different between forward
> and reverse processing, if an index or gpfn happens to be twice in
> the set. While that's perhaps not the usual thing to do, you never
> know how a creative user of the interface may find it useful to do so.

IIRC, I had gotten that from the arm guys.... it seems plausible to say
the mappings are unpredictable in case of repeated idx/gpfn, but I'll
see what they are doing to fix, or just change it myself here.

thanks for noticing,
Mukesh