Re: [PATCH v4] x86/xen: Add support for HVMOP_set_evtchn_upcall_vector

[Juergen Gross <jgross@xxxxxxxx>]

On 11.11.22 10:01, Juergen Gross wrote:
> On 08.11.22 17:26, Jan Beulich wrote:
> > On 03.11.2022 16:41, Jan Beulich wrote:
> > > On 03.11.2022 14:38, Jan Beulich wrote:
> > > > On 29.07.2022 09:04, Jane Malalane wrote:
> > > > > @@ -125,6 +130,9 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_xen_hvm_callback)
> > > > >   {
> > > > >       struct pt_regs *old_regs = set_irq_regs(regs);
> > > > > +    if (xen_percpu_upcall)
> > > > > +        ack_APIC_irq();
> > > > > +
> > > > >       inc_irq_stat(irq_hv_callback_count);
> > > > >       xen_hvm_evtchn_do_upcall();
> > > > > @@ -168,6 +176,15 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
> > > > >       if (!xen_have_vector_callback)
> > > > >           return 0;
> > > > > +    if (xen_percpu_upcall) {
> > > > > +        rc = xen_set_upcall_vector(cpu);
> > > >  From all I can tell at least for APs this happens before setup_local_apic().
> > > > With there being APIC interaction in this operation mode, as seen e.g. in
> > > > the earlier hunk above, I think this is logically wrong. And it leads to
> > > > apic_pending_intr_clear() issuing its warning: The vector registration, as
> > > > an intentional side effect, marks the vector as pending. Unless IRQs were
> > > > enabled at any point between the registration and the check, there's
> > > > simply no way for the corresponding IRR bit to be dealt with (by
> > > > propagating to ISR when the interrupt is delivered, and then being cleared
> > > > from ISR by EOI).
> > > With Roger's help I now have a pointer to osstest also exposing the issue:
> > >
> > > http://logs.test-lab.xenproject.org/osstest/logs/174592/test-amd64-amd64-xl-pvhv2-intel/huxelrebe0---var-log-xen-console-guest-debian.guest.osstest.log.gz
> > I've noticed only now that my mail to Jane bounced, and I'm now told
> > she's no longer in her role at Citrix. Since I don't expect to have time
> > to investigate an appropriate solution here, may I ask whether one of
> > the two of you could look into this, being the maintainers of this code?
> I think the correct way to handle this would be:
>
> - rename CPUHP_AP_ARM_XEN_STARTING to CPUHP_AP_XEN_STARTING
> - move the xen_set_upcall_vector() call to a new hotplug callback
>    registered for CPUHP_AP_XEN_STARTING (this can be done even
>    conditionally only if xen_percpu_upcall is set)
>
> Writing a patch now ...
For the APs this is working as expected.

The boot processor seems to be harder to fix. The related message is being
issued even with interrupts being on when setup_local_APIC() is called.

I've tried to register the callback only after the setup_local_APIC() call,
but this results in a system hang when the APs are started.

Any ideas?


Juergen

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