Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC

From	Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Newsgroups	linux.kernel
Subject	Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC
Date	2016-02-19 12:40 +0100
Message-ID	<r3RzI-4rt-3@gated-at.bofh.it> (permalink)
References	(5 earlier) <r2ODV-vy-41@gated-at.bofh.it> <r2R8K-21y-17@gated-at.bofh.it> <r2Seu-2Ye-15@gated-at.bofh.it> <r3xAZ-6Sq-3@gated-at.bofh.it> <r3xAZ-6Sq-1@gated-at.bofh.it>
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Hi,

On 2/18/16 21:18, Radim Krčmář wrote:
> 2016-02-18 09:25+0700, Suravee Suthikulpanit:
>> On 2/17/16 01:06, Radim Krčmář wrote:
>>> 2016-02-16 17:56+0100, Paolo Bonzini:
>>>>> On 16/02/2016 15:13, Radim Krčmář wrote:
>>>>>>> Yeah, I think atomic there means that it won't race with other writes to
>>>>>>> the same byte in IRR.  We're fine as long as AVIC writes IRR before
>>>>>>> checking IsRunning on every destination, which it seems to be.
>>>>>
>>>>> More precisely, if AVIC writes all IRRs (5.1) and ANDs all IsRunning
>>>>> flags before checking the result of the AND (6).
>>>>>
>>>>>>> (It would, but I believe that AVIC designers made it sane and the spec
>>>>>>>   doesn't let me read it in a way that supports your theories.)
>>>>>
>>>>> I hope so as well, and you've probably convinced me.  But I still think
>>>>> the code is wrong in this patch.  Let's look at the spec that you pasted:
>>> The code definitely is wrong.  I'll be more specific when disagreeing,
>>> sorry.
>>>
>>
>> Would you please be a bit more specific on what you think I am not doing
>> correctly to handle the #VMEXIT in the case of target not running below.
>>
>> +    case AVIC_INCMP_IPI_ERR_TARGET_NOT_RUN:
>> +        kvm_lapic_reg_write(apic, APIC_ICR2, icrh);
>> +        kvm_lapic_reg_write(apic, APIC_ICR, icrl);
>>
>> This is actually not just writing to the register. Please note that writing
>> to APIC_ICR register would also be calling apic_send_ipi(), which results in
>> injecting interrupts to the target core:
>
> Exactly.  Injecting the interrupt in AVIC_INCMP_IPI_ERR_TARGET_NOT_RUN
> handler is causing the double-injection bug that Paolo described.
>
>> Am I missing something?
>
> Probably that AVIC already wrote to all IRRs (and sent appropriate
> doorbells) before this VMEXIT, so KVM shouldn't repeat it.

Ah, Ok I got it now. Thanks for the detail description. I am still 
waiting to hear back from the hardware designer to confirm the HW 
behavior. Meanwhile, I have tried NOT setting the IRR, and only 
kick_vcpu(). And things seem to work fine. Therefore, I think your 
analysis is likely to be correct.

Thanks again,
Suravee

Thread

[PART1 RFC 0/9] KVM: x86: Introduce SVM AVIC support Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> - 2016-02-12 15:10 +0100
  [PART1 RFC 4/9] KVM: x86: Detect and Initialize AVIC support Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> - 2016-02-12 15:10 +0100
    Re: [PART1 RFC 4/9] KVM: x86: Detect and Initialize AVIC support Borislav Petkov <bp@alien8.de> - 2016-02-12 15:20 +0100
      Re: [PART1 RFC 4/9] KVM: x86: Detect and Initialize AVIC support Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> - 2016-02-12 16:50 +0100
  [PART1 RFC 9/9] svm: Manage vcpu load/unload when enable AVIC Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> - 2016-02-12 15:10 +0100
    Re: [PART1 RFC 9/9] svm: Manage vcpu load/unload when enable AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-12 16:50 +0100
  [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> - 2016-02-12 15:10 +0100
    Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Borislav Petkov <bp@alien8.de> - 2016-02-12 15:20 +0100
      Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> - 2016-02-12 17:00 +0100
        Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Borislav Petkov <bp@alien8.de> - 2016-02-12 18:20 +0100
          Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-12 19:30 +0100
            Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Borislav Petkov <bp@alien8.de> - 2016-02-12 19:40 +0100
              Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-12 20:00 +0100
                Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Borislav Petkov <bp@alien8.de> - 2016-02-12 20:40 +0100
                Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Ingo Molnar <mingo@kernel.org> - 2016-02-16 09:00 +0100
                [PATCH] x86/msr: Document msr-index.h rule for addition Borislav Petkov <bp@alien8.de> - 2016-02-16 09:40 +0100
    Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-12 17:00 +0100
      Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> - 2016-02-12 17:30 +0100
        Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-12 19:20 +0100
          Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> - 2016-02-12 20:40 +0100
          Re: [PART1 RFC 6/9] svm: Add interrupt injection via AVIC Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> - 2016-02-19 13:00 +0100
  [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> - 2016-02-12 15:10 +0100
    Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-12 16:40 +0100
      Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Radim Krčmář <rkrcmar@redhat.com> - 2016-02-15 20:30 +0100
      Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> - 2016-02-16 07:40 +0100
        Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-16 13:20 +0100
          Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Radim Krčmář <rkrcmar@redhat.com> - 2016-02-16 15:20 +0100
            Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-16 18:00 +0100
              Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Radim Krčmář <rkrcmar@redhat.com> - 2016-02-16 19:10 +0100
                Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Radim Krčmář <rkrcmar@redhat.com> - 2016-02-18 15:20 +0100
                Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 16:00 +0100
                Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Radim Krčmář <rkrcmar@redhat.com> - 2016-02-18 16:50 +0100
                Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 17:00 +0100
                Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Radim Krčmář <rkrcmar@redhat.com> - 2016-02-18 17:30 +0100
                Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 18:20 +0100
                Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Paolo Bonzini <pbonzini@redhat.com> - 2016-02-19 12:50 +0100
                Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> - 2016-02-19 12:40 +0100
  Re: [PART1 RFC 0/9] KVM: x86: Introduce SVM AVIC support Paolo Bonzini <pbonzini@redhat.com> - 2016-02-12 19:20 +0100
    Re: [PART1 RFC 0/9] KVM: x86: Introduce SVM AVIC support Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> - 2016-02-12 21:00 +0100
      Re: [PART1 RFC 0/9] KVM: x86: Introduce SVM AVIC support Paolo Bonzini <pbonzini@redhat.com> - 2016-02-12 21:10 +0100

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