On Thu, 2023-04-06 at 16:48 +0100, Peter Maydell wrote:
> On Thu, 2 Mar 2023 at 12:37, Paolo Bonzini <pbonz...@redhat.com> wrote:
> >
> > From: David Woodhouse <d...@amazon.co.uk>
> >
> > The way that Xen handles MSI PIRQs is kind of awful.
>
> > Now that this is working we can finally enable XENFEAT_hvm_pirqs and
> > let the guest use it all.
> >
>
> Hi; Coverity points out a logic error in this code (CID 1507603):
>
> > @@ -1638,6 +1877,7 @@ int xen_physdev_unmap_pirq(struct physdev_unmap_pirq
> > *unmap)
> >
> > /* We can only unmap GSI PIRQs */
> > if (gsi < 0) {
> > + qemu_mutex_unlock(&s->port_lock);
> > return -EINVAL;
> > }
>
> One of the things xen_physdev_unmap_pirq() does early is return
> if gsi is a negative value...
>
> > @@ -1646,6 +1886,12 @@ int xen_physdev_unmap_pirq(struct physdev_unmap_pirq
> > *unmap)
> > pirq_inuse_word(s, pirq) &= ~pirq_inuse_bit(pirq);
> >
> > trace_kvm_xen_unmap_pirq(pirq, gsi);
> > + qemu_mutex_unlock(&s->port_lock);
> > +
> > + if (gsi == IRQ_MSI_EMU) {
>
> ...but then later we try to test to see if it is IRQ_MSI_EMU.
> IRQ_MSI_EMU is -3, so this condition can never be true.
>
> > + kvm_update_msi_routes_all(NULL, true, 0, 0);
> > + }
>
> What was the intention here ?Hrm.... the way that Xen automatically maps the MSI to a PIRQ by snooping on the (masked) writes to the MSI target is awful, as noted. I don't think Linux guests ever do unmap the MSI PIRQ but it might be possible; I'll have to do some experiments in Xen to see what happens. Thanks.
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