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

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 19 October 2020 08:30
> To: paul@xxxxxxx
> Cc: 'Julien Grall' <julien@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx; '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>; 'Stefano Stabellini' <sstabellini@xxxxxxxxxx>
> Subject: Re: [PATCH 2/5] iommu / domctl: introduce XEN_DOMCTL_iommu_ctl
> 
> On 19.10.2020 09:23, Paul Durrant wrote:
> >> From: Julien Grall <julien@xxxxxxx>
> >> Sent: 16 October 2020 16:47
> >>
> >> 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.
> 
> But does this then need a #define? Starting valid command from 1
> ought to be sufficient?
> 

Seems harmless enough, and it also seemed the best way since to reserve 0 since 
this patch doesn't actually introduce any ops. As it has caused so much 
controversy though, I'll remove it.

  Paul

> Jan