Re: [PART1 RFC 0/9] KVM: x86: Introduce SVM AVIC support

From	Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Newsgroups	linux.kernel
Subject	Re: [PART1 RFC 0/9] KVM: x86: Introduce SVM AVIC support
Date	2016-02-12 21:00 +0100
Message-ID	<r1s2K-2YC-23@gated-at.bofh.it> (permalink)
References	<r1mA1-847-3@gated-at.bofh.it> <r1qtX-27E-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Hi,

On 2/13/16 01:13, Paolo Bonzini wrote:
> I have a few questions about AVIC.
>
> On 12/02/2016 14:59, Suravee Suthikulpanit wrote:
>> CURRENT UNSUPPORT USE-CASES
>> ===========================
>>      - Nested VM
>>      - VM Migration
>
> I'm interested in what you mean with "VM migration".  I've noticed that,
> because x2APIC is disabled by default, it's possible that a VM on a
> non-AVIC host will fail when moved to an AVIC host.  I would prefer if
> you kept x2APIC working through VMEXITs.  Getting the full performance
> benefit would require disabling x2APIC of course (or waiting for
> improved support in the processor), but at least there would be no surprise.
>
> Is it just this, or is there anything else?

For VM Migration, I meant the process of taking a snapshot of the VM and 
later on loading it back to resume where it left off, and not necessary 
to a different type of system. This would require saving off the VAPIC 
backing page of each vCPU along with the rest of per-VM AVIC data 
structures. IIUC, this might require changes in the QEmu as well.

Moving VM non-AVIC host to AVIC host, and vice versa, would be tricky.

I also see you points about supporting x2APIC. Let me look more into it, 
and then get back to you on this.

>
> (I'm quite surprised that x2APIC is not supported.  MSRs are faster than
> memory accesses due to the cost of TLB misses, which can be hefty for VMs).
>
> I have a few other doubts about the architecture that hopefully you (or
> Wei Huang too) can clarify before I can review this patch meaningfully.
>   I have replied to other patches with these questions.
>
> Paolo
>

I'll go through those and get back to you separately.

Regards,

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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