linux-kernel - Re: [PATCH v3] KVM: LAPIC: Fix lapic timer injection delay

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Date:   Thu, 29 Jun 2017 16:44:16 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v3] KVM: LAPIC: Fix lapic timer injection delay

2017-06-29 16:17 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
> 2017-06-29 15:55 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>>> +
>>> +            /* In case the sw timer triggered in the window */
>>> +            if (atomic_read(&apic->lapic_timer.pending) &&
>>> +                !apic_lvtt_period(apic))
>>> +                need_cancel = true;
>>> +            else if (r && (apic_lvtt_oneshot(apic) ||
>>> apic_lvtt_tscdeadline(apic)))
>>> +                apic_timer_expired(apic);
>>> +        }
>>> +    }
>
> [...]
>
>>
>> You still need to enable the preemption timer even if you return 1, so
>> in lapic.c it becomes
>>
>>         if (!apic_lvtt_period(apic)) {
>>                 if (r)
>>                         apic_timer_expired(apic);
>>                 if (atomic_read(&apic->lapic_timer.pending))
>>                         need_cancel = true;
>>         }
>
> I think the codes are more clear but the same as above. We didn't
> program preemption timer vmcs field if delta == 0, so how to
> understand "need to enable the preemption timer even if return 1"?

I guess you mean start_hv_timer() should return true, right?

Regards,
Wanpeng Li