Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map

From	Radim Krčmář <rkrcmar@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map
Date	2016-07-01 18:00 +0200
Message-ID	<rQ91f-8tu-17@gated-at.bofh.it> (permalink)
References	(4 earlier) <rQ63o-6GX-9@gated-at.bofh.it> <rQ7iO-7C4-5@gated-at.bofh.it> <rQ7LQ-7MG-11@gated-at.bofh.it> <rQ8eR-8cq-1@gated-at.bofh.it> <rQ8ox-8fN-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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2016-07-01 17:12+0200, Paolo Bonzini:
> On 01/07/2016 17:06, Paolo Bonzini wrote:
>>>> >> > Should it?
>>> Yes, x2APIC ID cannot be changed in hardware and is initialized to the
>>> intitial APIC ID.
>>> Letting LAPIC_SET change x2APIC ID would allow scenarios where userspace
>>> reuses old VMs instead of building new ones after reconfiguration.
>>> I don't think it's a sensible use case and it it is currently broken,
>>> because we don't exit to userspace when changing APIC mode, so KVM would
>>> just set APIC ID to VCPU ID on any transition and userspace couldn't
>>> amend it.
> 
> Forgot to reply about this: letting SET_LAPIC change x2APIC IDs is nonsense.
> 
> In x2APIC mode + new capability disabled SET_LAPIC should ignore the id
> register altogether for backwards compatibility.

I'd still shift SET_LAPIC APIC ID to have internal APIC ID register in
hardware-compatible format.

> In x2APIC mode + new capability enabled it should either ignore it, or
> fail if the x2APIC ID doesn't match the VCPU id.  I suspect the latter
> is better because it would help catching the case where userspace is
> erroneously shifting the id left to bits 31-24.

Yes, I'll make it EINVAL.

Thread

[PATCH v1 00/11] KVM: x86: break the xAPIC barrier Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
  [PATCH v1 06/11] KVM: x86: use hardware-compatible format for APIC ID register Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
    Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for  APIC ID register Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 10:40 +0200
      Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for  APIC ID register Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 15:20 +0200
        Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for  APIC ID register Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 16:20 +0200
          Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for  APIC ID register Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 17:00 +0200
            Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for  APIC ID register Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 17:10 +0200
              Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for  APIC ID register Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 18:00 +0200
                Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for  APIC ID register Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 18:40 +0200
  [PATCH v1 10/11] KVM: x86: add KVM_CAP_X2APIC_API Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
    Re: [PATCH v1 10/11] KVM: x86: add KVM_CAP_X2APIC_API Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 10:30 +0200
      Re: [PATCH v1 10/11] KVM: x86: add KVM_CAP_X2APIC_API Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 15:30 +0200
    Re: [PATCH v1 10/11] KVM: x86: add KVM_CAP_X2APIC_API David Matlack <dmatlack@google.com> - 2016-07-01 20:20 +0200
      Re: [PATCH v1 10/11] KVM: x86: add KVM_CAP_X2APIC_API Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 20:40 +0200
  [PATCH v1 04/11] KVM: x86: use u16 for logical VCPU mask in lapic Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
    Re: [PATCH v1 04/11] KVM: x86: use u16 for logical VCPU mask in lapic Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 10:20 +0200
      Re: [PATCH v1 04/11] KVM: x86: use u16 for logical VCPU mask in lapic Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 14:50 +0200
        Re: [PATCH v1 04/11] KVM: x86: use u16 for logical VCPU mask in lapic Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 16:20 +0200
  [PATCH v1 07/11] KVM: VMX: optimize APIC ID read with APICv Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
  [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
    Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Andrew Honig <ahonig@google.com> - 2016-07-01 00:20 +0200
      Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 10:50 +0200
        Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 14:50 +0200
          Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 16:10 +0200
            Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 16:40 +0200
              Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 17:10 +0200
                Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 17:20 +0200
                Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 18:00 +0200
                Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 18:40 +0200
                Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 17:40 +0200
    Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 09:40 +0200
  [PATCH v1 01/11] KVM: x86: bump KVM_SOFT_MAX_VCPUS to 240 Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
    Re: [PATCH v1 01/11] KVM: x86: bump KVM_SOFT_MAX_VCPUS to 240 Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 10:50 +0200
  [PATCH v1 05/11] KVM: x86: use generic function for MSI parsing Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
  [PATCH v1 11/11] KVM: x86: bump MAX_VCPUS to 288 Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
    Re: [PATCH v1 11/11] KVM: x86: bump MAX_VCPUS to 288 Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 10:50 +0200
  [PATCH v1 09/11] KVM: x86: reset lapic base in kvm_lapic_reset Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
    Re: [PATCH v1 09/11] KVM: x86: reset lapic base in kvm_lapic_reset Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 10:50 +0200
  [PATCH v1 02/11] KVM: x86: add kvm_apic_map_get_dest_lapic Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200
    Re: [PATCH v1 02/11] KVM: x86: add kvm_apic_map_get_dest_lapic Paolo Bonzini <pbonzini@redhat.com> - 2016-07-01 10:00 +0200
      Re: [PATCH v1 02/11] KVM: x86: add kvm_apic_map_get_dest_lapic Radim Krčmář <rkrcmar@redhat.com> - 2016-07-01 14:50 +0200
  [PATCH v1 08/11] KVM: x86: directly call recalculate_apic_map on lapic restore Radim Krčmář <rkrcmar@redhat.com> - 2016-06-30 23:00 +0200

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