Re: [V8 PATCH 7/8] pvh dom0: add check for pvh in vioapic_range

[Mukesh Rathor <mukesh.rathor@oracle.com>]

On Mon, 7 Apr 2014 10:28:50 +0100
George Dunlap <george.dunlap@eu.citrix.com> wrote:

> On 04/07/2014 07:59 AM, Jan Beulich wrote:
> >>>> On 05.04.14 at 03:00, <mukesh.rathor@oracle.com> wrote:
> >> On Tue, 01 Apr 2014 16:09:15 +0100
> >> "Jan Beulich" <JBeulich@suse.com> wrote:
> >>
> >>>>>> On 01.04.14 at 16:40, <george.dunlap@eu.citrix.com> wrote:
> >>>> On 03/24/2014 09:34 AM, Jan Beulich wrote:
> >>>>>>>> On 22.03.14 at 02:39, <mukesh.rathor@oracle.com> wrote:
> >>>>>> --- a/xen/arch/x86/hvm/vioapic.c
> >>>>>> +++ b/xen/arch/x86/hvm/vioapic.c
> >>>>>> @@ -238,8 +238,13 @@ static int vioapic_write(
> >>>>>>
> >>>>>>    static int vioapic_range(struct vcpu *v, unsigned long addr)
> >>>>>>    {
> >>>>>> -    struct hvm_hw_vioapic *vioapic =
> >>>>>> domain_vioapic(v->domain);
> >>>>>> +    struct hvm_hw_vioapic *vioapic;
> >>>>>> +
> >>>>>> +    /* pvh uses event channel callback */
> >>>>>> +    if ( is_pvh_vcpu(v) )
> >>>>>> +        return 0;
> >>>>>>
> >>>>>> +    vioapic = domain_vioapic(v->domain);
> >>>>> I can see why the extra check is needed, but I can't see why you
> >>>>> convert the initializer to an assignment: Afaict
> >>>>> domain_vioapic() is safe even if d->arch.hvm_domain.vioapic ==
> >>>>> NULL.
> >>>> Or better yet, just make it something like:
> >>>>
> >>>> return vioapic && ((addr >= [...original range check]))
> >>>>
> >>>> That way we don't have to have a PVH-specific hook at all.  If a
> >>>> domain doesn't have a vioapic for any reason, return 0.
> >>> No, vioapic isn't going to be NULL for PVH:
> >>>
> >>> #define domain_vioapic(d)
> >>> (&(d)->arch.hvm_domain.vioapic->hvm_hw_vioapic)
> >> No, viopaic is NULL for PVH, hence the patch. So, can prob just
> >> check for the ptr like George suggests and remove the pvh check.
> > Sorry, no - I agree that d->arch.hvm_domain.vioapic is NULL for
> > PVH, but that doesn't mean the result of domain_vioapic(d) is too
> > (see the quoted #define above).
> 
> I interpreted Mukesh saying "check for the ptr" as, "check 
> d->arch_hvm.domain.vioapic", not "check domain_vioapic(d)".

Correct. Since, vioapic is NULL for PVH, domain_vioapic(d) will
result in NULL ptr exception for PVH, so we can't call that macro
for PVH.

thanks
Mukesh