Re: [Xen-devel] [PATCH v8 2/7] VMX: Properly handle pi when all the assigned devices are removed

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Wu, Feng
> Sent: Friday, November 18, 2016 12:27 PM
> > > diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
> > > index 8bce213..e71732f 100644
> > > --- a/xen/drivers/passthrough/pci.c
> > > +++ b/xen/drivers/passthrough/pci.c
> > > @@ -1602,6 +1602,13 @@ int iommu_do_pci_domctl(
> > >          break;
> > >
> > >      case XEN_DOMCTL_assign_device:
> > > +        /* no domain_pause() */
> > > +        if ( d == current->domain )
> > > +        {
> > > +            ret = -EINVAL;
> > > +            break;
> > > +        }
> > > +
> >
> > don't understand why adding above check, and why "no domain_pause"
> > matters in this change.
> 
> In fact, this change is according Jan's following comments on v6:
> 
> " There's one additional caveat here which no-one of us so far thought
> of: Currently there's nothing preventing the domctl-s under which
> this sits from being issued by the control domain for itself. Various
> other domctl-s, however, guard against this case when intending
> to pause the target domain. The same needs to be done for the
> ones leading here."
> 
> We need to prevent the domain from pausing itself.
> 

XEN_DOMCTL_assign_device doesn't imply a domain_pause operation,
at least not obvious in this level. If we don't have PI enabled underneath,
is above guard still necessary? If the answer is yes, the comment should
be elaborated for easy understanding... :-)

Thanks
Kevin

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