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Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff

From David Hildenbrand <david@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff
Date 2016-12-05 15:40 +0100
Message-ID <sL2AV-5Jq-5@gated-at.bofh.it> (permalink)
References <sK20h-82t-3@gated-at.bofh.it> <sK20i-82t-47@gated-at.bofh.it>
Organization Red Hat GmbH

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Am 02.12.2016 um 20:44 schrieb Radim Krčmář:
> LAPIC after reset is in xAPIC mode, which poses a problem for hotplug of
> VCPUs with high APIC ID, because reset VCPU is waiting for INIT/SIPI,
> but there is no way to uniquely address it using xAPIC.
>
> From many possible options, we chose the one that also works on real
> hardware: accepting interrupts addressed to LAPIC's x2APIC ID even in
> xAPIC mode.
>
> KVM intentionally differs from real hardware, because real hardware
> (Knights Landing) does just "x2apic_id & 0xff" to decide whether to
> accept the interrupt in xAPIC mode and it can deliver one interrupt to
> more than one physical destination, e.g. 0x123 to 0x123 and 0x23.
>
> Add a capability to let userspace know that we do something now.

Should we allow user space to turn it on/off for compatibility handling? 
Or do we just not care? (or how will this capability be used later on?)



-- 

David

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[PATCH 0/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff Radim Krčmář <rkrcmar@redhat.com> - 2016-12-02 20:50 +0100
  [PATCH 2/4] KVM: x86: replace kvm_apic_id with kvm_{x,x2}apic_id Radim Krčmář <rkrcmar@redhat.com> - 2016-12-02 20:50 +0100
  [PATCH 3/4] KVM: x86: make interrupt delivery fast and slow path behave the same Radim Krčmář <rkrcmar@redhat.com> - 2016-12-02 20:50 +0100
  [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff Radim Krčmář <rkrcmar@redhat.com> - 2016-12-02 20:50 +0100
    Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over  0xff David Hildenbrand <david@redhat.com> - 2016-12-05 15:40 +0100
      Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over  0xff Radim Krčmář <rkrcmar@redhat.com> - 2016-12-05 17:10 +0100
        Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over  0xff David Hildenbrand <david@redhat.com> - 2016-12-05 19:10 +0100
          Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over  0xff Radim Krčmář <rkrcmar@redhat.com> - 2016-12-05 22:00 +0100
            Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over  0xff David Hildenbrand <david@redhat.com> - 2016-12-06 10:50 +0100
              Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over  0xff Radim Krčmář <rkrcmar@redhat.com> - 2016-12-06 14:00 +0100
    Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over  0xff Paolo Bonzini <pbonzini@redhat.com> - 2016-12-07 13:10 +0100
      Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over  0xff Radim Krčmář <rkrcmar@redhat.com> - 2016-12-07 16:50 +0100

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