Re: [PATCH 2/5] iommu / domctl: introduce XEN_DOMCTL_iommu_ctl

[Julien Grall <julien@xxxxxxx>]

Hi Paul,

On 19/10/2020 08:23, Paul Durrant wrote:
> > -----Original Message-----
> > From: Julien Grall <julien@xxxxxxx>
> > Sent: 16 October 2020 16:47
> > To: Paul Durrant <paul@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: Paul Durrant <pdurrant@xxxxxxxxxx>; Daniel De Graaf 
> > <dgdegra@xxxxxxxxxxxxx>; Ian Jackson
> > <iwj@xxxxxxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Andrew Cooper 
> > <andrew.cooper3@xxxxxxxxxx>; George Dunlap
> > <george.dunlap@xxxxxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Stefano Stabellini
> > <sstabellini@xxxxxxxxxx>
> > Subject: Re: [PATCH 2/5] iommu / domctl: introduce XEN_DOMCTL_iommu_ctl
> >
> > Hi Paul,
> >
> > On 05/10/2020 10:49, Paul Durrant wrote:
> > > diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
> > > index 791f0a2592..75e855625a 100644
> > > --- a/xen/include/public/domctl.h
> > > +++ b/xen/include/public/domctl.h
> > > @@ -1130,6 +1130,18 @@ struct xen_domctl_vuart_op {
> > >                                     */
> > >    };
> > >
> > > +/*
> > > + * XEN_DOMCTL_iommu_ctl
> > > + *
> > > + * Control of VM IOMMU settings
> > > + */
> > > +
> > > +#define XEN_DOMCTL_IOMMU_INVALID 0
> > I can't find any user of XEN_DOMCTL_IOMMU_INVALID. What's the purpose
> > for it?
> It's just a placeholder. I think it's generally safer that a zero opcode value 
> is invalid.
Thanks for the explanation. I first thought the goal would to somehow 
invalidate the IOMMU :).
Anyway, it might be worth adding /* Reserved - should never be used */ 
on top.
Cheers,

--
Julien Grall