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Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index |
Date: |
Wed, 14 Jun 2017 15:11:17 +0200 |
On Wed, 14 Jun 2017 10:01:49 -0300
Eduardo Habkost <address@hidden> wrote:
> On Wed, Jun 14, 2017 at 01:26:44PM +0200, Paolo Bonzini wrote:
> >
> >
> > On 14/06/2017 13:25, Roman Kagan wrote:
> > >> The problem with that is that it will break as soon as we create
> > >> VCPUs in a different order. Unsolvable on hosts that don't allow
> > >> HV_X64_MSR_VP_INDEX to be set, however.
> > > Right, thanks for putting together a detailed explanation.
> > >
> > > This was a thinko back then, not to have HV_X64_MSR_VP_INDEX maintained
> > > by QEMU. I'm going to post a patch to KVM fixing that.
> > >
> > > Meanwhile QEMU needs a way to maintain its notion of vp_index that is
> > > 1) in sync with kernel's notion
> > > 2) also with kernels that don't support setting the msr
> > > 3) persistent across migrations
> > >
> > > cpu_index looked like a perfect candidate.
> > >
> >
> > What you want is the APIC id, which _is_ cpu_index but may not be in the
> > future. But the APIC id is also the KVM vcpu_id, so there's no need to
> > have VP_INDEX maintained by QEMU.
>
> No, KVM really uses the VCPU _index_ for HV_X64_MSR_VP_INDEX:
and as you pointed out that works just by luck,
as soon as we there would be out of order created CPUs
returned value won't match cpu_index.
So instead of spreading this nonsense out to QEMU, is it possible
to fix kernel(kvm+guest) to use apic_id instead?
> kvm_hv_get_msr():
>
> case HV_X64_MSR_VP_INDEX: {
> int r;
> struct kvm_vcpu *v;
>
> kvm_for_each_vcpu(r, v, vcpu->kvm) {
> if (v == vcpu) {
> data = r;
> break;
> }
> }
> break;
> }
>
>
- [Qemu-devel] [PATCH 03/23] hyperv: set partition-wide MSRs only on first vcpu, (continued)
- [Qemu-devel] [PATCH 03/23] hyperv: set partition-wide MSRs only on first vcpu, Roman Kagan, 2017/06/06
- [Qemu-devel] [PATCH 01/23] hyperv: add header with protocol definitions, Roman Kagan, 2017/06/06
- [Qemu-devel] [PATCH 02/23] update-linux-headers: prepare for hyperv.h removal, Roman Kagan, 2017/06/06
- [Qemu-devel] [PATCH 06/23] hyperv: helper to find vcpu by VP index, Roman Kagan, 2017/06/06
- [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Roman Kagan, 2017/06/06
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Eduardo Habkost, 2017/06/13
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Roman Kagan, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Paolo Bonzini, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Igor Mammedov, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Eduardo Habkost, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index,
Igor Mammedov <=
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Paolo Bonzini, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Eduardo Habkost, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Paolo Bonzini, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Igor Mammedov, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Eduardo Habkost, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Roman Kagan, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Eduardo Habkost, 2017/06/14
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Paolo Bonzini, 2017/06/15
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Roman Kagan, 2017/06/15
- Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index, Paolo Bonzini, 2017/06/15