Re: [Xen-devel] [PATCH v2 07/16] x86: put XEN_DOMCTL_{set, get}_address_size under CONFIG_PV

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Oct 31, 2018 at 03:47:25AM -0600, Jan Beulich wrote:
> >>> On 31.10.18 at 10:33, <wei.liu2@xxxxxxxxxx> wrote:
> > On Wed, Oct 31, 2018 at 03:00:17AM -0600, Jan Beulich wrote:
> >> >>> On 30.10.18 at 21:50, <wei.liu2@xxxxxxxxxx> wrote:
> >> > On Mon, Oct 29, 2018 at 08:28:07AM -0600, Jan Beulich wrote:
> >> >> >>> On 19.10.18 at 16:28, <wei.liu2@xxxxxxxxxx> wrote:
> >> >> > --- a/xen/arch/x86/domctl.c
> >> >> > +++ b/xen/arch/x86/domctl.c
> >> >> > @@ -608,6 +608,7 @@ long arch_do_domctl(
> >> >> >              copyback = true;
> >> >> >          break;
> >> >> >  
> >> >> > +#ifdef CONFIG_PV
> >> >> >      case XEN_DOMCTL_set_address_size:
> >> >> >          if ( ((domctl->u.address_size.size == 64) && 
> >> >> > !d->arch.is_32bit_pv) ||
> >> >> >               ((domctl->u.address_size.size == 32) && 
> >> >> > d->arch.is_32bit_pv) )
> >> >> > @@ -623,6 +624,7 @@ long arch_do_domctl(
> >> >> >                                                                
> >> >> > BITS_PER_LONG;
> >> >> >          copyback = true;
> >> >> >          break;
> >> >> > +#endif
> >> >> 
> >> >> ... add such a check so that similar behavior will result with PV
> >> >> enabled and disabled (error codes may differ, but success vs
> >> >> error ought to match).
> >> > 
> >> > I don't follow. Do you mean adding is_pv_domain check somewhere?
> >> 
> >> Yes. Otherwise behavior differs between a PV and a !PV hypervisor.
> > 
> > I'm still at a loss to figure out what "similar behavior" you want. When
> > you say behaviour differs, do you mean the lack of copyback in my patch?
> > Why would that be relevant to a ENOSYS hypercall?
> 
> With !PV you'd get -ENOSYS (which is wrong in its own right, but
> that a different topic). With PV you'd not get any error under at
> least some conditions even for a HVM domain (if you don't make it
> into switch_compat()), afaict.

Right, so you actually wanted me to fix two issues.

One is to change it to not return -ENOSYS. I think you would want
-EOPNOTSUPP instead?

The other is to tighten the hypercalls to be PV only. I think for HVM
guests they should return -EINVAL.

So instead of putting the pair under CONFIG_PV, I should be adding some
checks to them individually to do what we agree on later. Does this make
sense?

Wei.

> 
> Jan
> 
> 

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