Re: [PATCH for-4.14 2/2] x86/passthrough: introduce a flag for GSIs not requiring an EOI or unmask

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Jun 10, 2020 at 01:37:15PM +0100, Andrew Cooper wrote:
> On 10/06/2020 12:51, Roger Pau Monne wrote:
> > @@ -920,6 +927,11 @@ static void hvm_dirq_assist(struct domain *d, struct 
> > hvm_pirq_dpci *pirq_dpci)
> >          if ( pirq_dpci->flags & HVM_IRQ_DPCI_IDENTITY_GSI )
> >          {
> >              hvm_gsi_assert(d, pirq->pirq);
> > +            if ( pirq_dpci->flags & HVM_IRQ_DPCI_NO_EOI )
> > +            {
> > +                spin_unlock(&d->event_lock);
> > +                return;
> > +            }
> 
> Urgh.  Could I possibly talk you into fixing hvm_dirq_assist() to have a
> "goto out;" and a single unlock path ?  (How far are you expecting this
> to be backported?)

I was very tempted to go that way but didn't want to introduce more
churn. Since you agree I will do so.

> I'm also totally unconvinced that the atomic test_and_clear() needs to
> be done with the event lock held (it should either be non-atomic, or the
> locking should be inside the if() condition), but that is probably not a
> can of worms wanting opening right now...

There's some reasoning about all this in 104072fc1c7e6ed. I also think
naming it masked is confusing, since the underlying interrupt might
not be masked. Anyway, this seems like something I don't really want
to get into now, as it seems quite fragile.

Thanks, Roger.