linux-kernel - Re: [PATCH v4] x86/xen: Add support for HVMOP_set_evtchn_upcall

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Date:   Tue, 8 Nov 2022 17:26:48 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Maximilian Heyne <mheyne@...zon.de>,
        xen-devel@...ts.xenproject.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] x86/xen: Add support for
 HVMOP_set_evtchn_upcall_vector

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?

Thanks, Jan