Re: [Xen-devel] [PATCH v4 12/12] x86/hvm/ioreq: add a new mappable resource type...

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Sep 07, 2017 at 03:59:05PM +0100, Wei Liu wrote:
> On Thu, Sep 07, 2017 at 03:56:16PM +0100, Roger Pau Monné wrote:
> > On Tue, Sep 05, 2017 at 12:37:16PM +0100, Paul Durrant wrote:
[...]
> > > +        /* Make sure the page has not been allocated */
> > > +        if ( gfn_eq(iorp->gfn, INVALID_GFN) )
> > > +            return -EPERM;
> > > +
> > > +        return 0;
> > > +    }
> > > +
> > >      if ( d->is_dying )
> > >          return -EINVAL;
> > >  
> > > @@ -272,6 +281,57 @@ static int hvm_map_ioreq_gfn(struct hvm_ioreq_server 
> > > *s, bool buf)
> > >      return rc;
> > >  }
> > >  
> > > +static int hvm_alloc_ioreq_mfn(struct hvm_ioreq_server *s, bool buf)
> > > +{
> > > +    struct domain *currd = current->domain;
> > > +    struct hvm_ioreq_page *iorp = buf ? &s->bufioreq : &s->ioreq;
> > > +
> > > +    if ( iorp->page )
> > > +    {
> > > +        /* Make sure the page has not been mapped */
> > 
> > Maybe it's just me being slightly lost, but here you imply that
> > iorp->gfn being != INVALID_GFN means the page is mapped, while above
> > you mention allocated for the same check.
> > 
> > Is it because gfn has different usages depending on the context?
> > 
> 
> Haha, I'm not the only one who got confused while reading the patch. ;-)
> 
> That's because the "page" can be obtained via two different methods.
> 
> "Allocated" means getting it from xen heap, "mapped" means mapping guest
> page afaict.

Oh, thanks. I think the comment should be slightly expanded then to
give more context, or else someone else is likely to trip over this
again IMHO.

Roger.

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