Re: [Xen-devel] [PATCH v7 1/6] x86/domain: remove the 'oos_off' flag

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 02 September 2019 15:12
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap 
> <George.Dunlap@xxxxxxxxxx>; Roger Pau
> Monne <roger.pau@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx; Tim (Xen.org) 
> <tim@xxxxxxx>; WeiLiu
> <wl@xxxxxxx>
> Subject: Re: [PATCH v7 1/6] x86/domain: remove the 'oos_off' flag
> 
> On 02.09.2019 15:59, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Jan Beulich <jbeulich@xxxxxxxx>
> >> Sent: 02 September 2019 14:46
> >> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> >> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap 
> >> <George.Dunlap@xxxxxxxxxx>; Roger Pau
> >> Monne <roger.pau@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx; Tim 
> >> (Xen.org) <tim@xxxxxxx>; WeiLiu
> >> <wl@xxxxxxx>
> >> Subject: Re: [PATCH v7 1/6] x86/domain: remove the 'oos_off' flag
> >>
> >> On 02.09.2019 15:06, Paul Durrant wrote:
> >>>> From: Jan Beulich <jbeulich@xxxxxxxx>
> >>>> Sent: 02 September 2019 13:34
> >>>>
> >>>> On 30.08.2019 10:29, Paul Durrant wrote:
> >>>>> --- a/xen/common/domain.c
> >>>>> +++ b/xen/common/domain.c
> >>>>> @@ -313,11 +313,19 @@ static int sanitise_domain_config(struct 
> >>>>> xen_domctl_createdomain *config)
> >>>>>          return -EINVAL;
> >>>>>      }
> >>>>>
> >>>>> -    if ( !(config->flags & XEN_DOMCTL_CDF_hvm_guest) &&
> >>>>> -         (config->flags & XEN_DOMCTL_CDF_hap) )
> >>>>> +    if ( !(config->flags & XEN_DOMCTL_CDF_hvm_guest) )
> >>>>>      {
> >>>>> -        dprintk(XENLOG_INFO, "HAP requested for non-HVM guest\n");
> >>>>> -        return -EINVAL;
> >>>>> +        if ( config->flags & XEN_DOMCTL_CDF_hap )
> >>>>> +        {
> >>>>> +            dprintk(XENLOG_INFO, "HAP requested for non-HVM guest\n");
> >>>>> +            return -EINVAL;
> >>>>> +        }
> >>>>> +
> >>>>> +        /*
> >>>>> +         * It is only meaningful for XEN_DOMCTL_CDF_oos_off to be clear
> >>>>> +         * for HVM guests.
> >>>>> +         */
> >>>>> +        config->flags |= XEN_DOMCTL_CDF_oos_off;
> >>>>
> >>>> ... I wonder whether this last part wouldn't better belong into
> >>>> x86's arch_sanitise_domain_config(). Arm, to the contrary, should
> >>>> force/require the bit to be uniformly off.
> >>>>
> >>>
> >>> I'm sure I had a reason for doing it like this but it's sufficiently long
> >>> ago now that I've forgotten what it was*. Would it be ok to take the code
> >>> as-is and I'll investigate whether this can be tidied up?
> >>
> >> Well, with this pending question I'm less inclined to stop waiting for
> >> the outstanding acks.
> >>
> >>> [ * I suspect it was concern over breaking existing tool-stacks by
> >>> requiring them to set a flag that previously they did not need to, but
> >>> I'm not sure that was the only reason ]
> >>
> >> Seems rather unlikely to me, as there wouldn't be any difference (from
> >> tool stack perspective) if the adjustment was done by per-arch code.
> >
> > Ok, if you feel strongly about it I'll move the hunk.
> 
> Well, wait - not the hunk. The HAP part should remain in common code
> imo. The OOS part wants doing differently in x86 and Arm code.
> 

Yes, the hap part stays put. The 'oos_off' part moves to x86 and arm can be 
left alone because it already rejects flags != (hvm | hap).

  Paul

> Jan
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