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Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry

From Radim Krčmář <rkrcmar@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry
Date 2016-11-03 19:10 +0100
Message-ID <szuCB-7nG-13@gated-at.bofh.it> (permalink)
References (1 earlier) <ssfp1-4T2-55@gated-at.bofh.it> <swCwF-8id-3@gated-at.bofh.it> <szqpj-4t0-21@gated-at.bofh.it> <szrOq-5vm-21@gated-at.bofh.it> <szsKu-664-45@gated-at.bofh.it>
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2016-11-03 17:00+0100, Paolo Bonzini:
> On 03/11/2016 16:03, Radim Krčmář wrote:
>> 2016-11-03 14:30+0100, Paolo Bonzini:
>>> On 26/10/2016 21:59, Radim Krčmář wrote:
>>>> 2016-10-14 20:21+0200, Paolo Bonzini:
>>>>> Calling apic_find_highest_irr results in IRR being scanned twice,
>>>>> once in vmx_sync_pir_from_irr and once in apic_search_irr.  Change
>>>>> sync_pir_from_irr to do the RVI write and kvm_apic_update_irr to
>>>>> compute the new RVI on the fly.
>>>>>
>>>>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>>>> ---
>>>>
>>>> Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
>>>
>>> Nope, this breaks nested VMX exit on external interrupt.  For now I'm
>>> testing only patch 1 and will push that one only to kvm/next.

Which hypervisor is being nested?

>> Hm, does it also happen with this change?
> 
> Probably not but I wanted to understand why. :)

Yeah, I'm also looking forward to knowing the funny coincidence.

I think a bug is likely for hypervisors that don't enable
PIN_BASED_EXT_INTR_MASK.  The bug would trigger when
kvm_cpu_has_interrupt() in vmx_check_nested_events() in
kvm_arch_vcpu_runnable() queues the interrupt ...
but I didn't see how this would have caused a problem. :)

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Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-03 14:40 +0100
  Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-11-03 15:00 +0100
    Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-03 17:10 +0100
  Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-11-03 16:10 +0100
    Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-03 17:10 +0100
      Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-11-03 19:10 +0100
        Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-03 19:20 +0100
          Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-11-03 19:30 +0100
            Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-11-03 21:20 +0100
              Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-04 10:40 +0100

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