Re: [Xen-devel] [PATCH v6 2/7] VMX: Properly handle pi when all the assigned devices are removed

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Thursday, November 3, 2016 5:08 PM
> To: Wu, Feng <feng.wu@xxxxxxxxx>
> Cc: andrew.cooper3@xxxxxxxxxx; dario.faggioli@xxxxxxxxxx;
> george.dunlap@xxxxxxxxxxxxx; Tian, Kevin <kevin.tian@xxxxxxxxx>; xen-
> devel@xxxxxxxxxxxxx
> Subject: RE: [PATCH v6 2/7] VMX: Properly handle pi when all the assigned
> devices are removed
> 
> >>> On 03.11.16 at 08:45, <feng.wu@xxxxxxxxx> wrote:
> 
> >
> >> -----Original Message-----
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: Friday, October 28, 2016 9:19 PM
> >> To: Wu, Feng <feng.wu@xxxxxxxxx>
> >> Cc: andrew.cooper3@xxxxxxxxxx; dario.faggioli@xxxxxxxxxx;
> >> george.dunlap@xxxxxxxxxxxxx; Tian, Kevin <kevin.tian@xxxxxxxxx>; xen-
> >> devel@xxxxxxxxxxxxx
> >> Subject: Re: [PATCH v6 2/7] VMX: Properly handle pi when all the assigned
> >> devices are removed
> >>
> >> >>> On 28.10.16 at 04:37, <feng.wu@xxxxxxxxx> wrote:
> >> > @@ -215,11 +220,21 @@ void vmx_pi_hooks_assign(struct domain *d)
> >> >  /* This function is called when pcidevs_lock is held */
> >> >  void vmx_pi_hooks_deassign(struct domain *d)
> >> >  {
> >> > +    struct vcpu *v;
> >> > +
> >> >      if ( !iommu_intpost || !has_hvm_container_domain(d) )
> >> >          return;
> >> >
> >> >      ASSERT(d->arch.hvm_domain.vmx.vcpu_block);
> >> >
> >> > +    /*
> >> > +     * Pausing the domain can make sure the vCPU is not
> >> > +     * running and hence not calling the hooks simultaneously
> >> > +     * when deassigning the PI hooks and removing the vCPU
> >> > +     * from the blocking list.
> >> > +     */
> >> > +    domain_pause(d);
> >>
> >> 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.
> >
> > Thanks for the comments! Could you share in which case can a domain
> > attach/detach a device for itself? Thanks!
> 
> That's not the question. The code path needs to be safe, just like
> all others (which we also expect Dom0 - or any other eligible domain
> - to not use with itself as the target domain).

Sure, got it!

Thanks,
Feng

> 
> Jan


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