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

[Juergen Gross <jgross@suse.com>]

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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 ...


Juergen

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