Re: [Xen-devel] [PATCH RFC V6 1/5] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

[Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>]

On 04/27/2012 09:23 PM, Gleb Natapov wrote:
> On Fri, Apr 27, 2012 at 04:15:35PM +0530, Raghavendra K T wrote:
> > On 04/24/2012 03:29 PM, Gleb Natapov wrote:
> > > On Mon, Apr 23, 2012 at 03:29:47PM +0530, Raghavendra K T wrote:
> > > > From: Srivatsa Vaddagiri<vatsa@xxxxxxxxxxxxxxxxxx>
> > > >
> > > > KVM_HC_KICK_CPU allows the calling vcpu to kick another vcpu out of halt state.
> > > >
> > > > The presence of these hypercalls is indicated to guest via
> > > > KVM_FEATURE_PV_UNHALT/KVM_CAP_PV_UNHALT.
> > > >
> > > > Signed-off-by: Srivatsa Vaddagiri<vatsa@xxxxxxxxxxxxxxxxxx>
> > > > Signed-off-by: Suzuki Poulose<suzuki@xxxxxxxxxx>
> > > > Signed-off-by: Raghavendra K T<raghavendra.kt@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > [...]
> > > > +/*
> > > > + * kvm_pv_kick_cpu_op:  Kick a vcpu.
> > > > + *
> > > > + * @apicid - apicid of vcpu to be kicked.
> > > > + */
> > > > +static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
> > > > +{
> > > > +       struct kvm_vcpu *vcpu = NULL;
> > > > +       int i;
> > > > +
> > > > +       kvm_for_each_vcpu(i, vcpu, kvm) {
> > > > +               if (!kvm_apic_present(vcpu))
> > > > +                       continue;
> > > > +
> > > > +               if (kvm_apic_match_dest(vcpu, 0, 0, apicid, 0))
> > > > +                       break;
> > > > +       }
> > > > +       if (vcpu) {
> > > > +               /*
> > > > +                * Setting unhalt flag here can result in spurious runnable
> > > > +                * state when unhalt reset does not happen in vcpu_block.
> > > > +                * But that is harmless since that should soon result in halt.
> > > > +                */
> > > > +               vcpu->arch.pv.pv_unhalted = 1;
> > > > +               /* We need everybody see unhalt before vcpu unblocks */
> > > > +               smp_mb();
> > > > +               kvm_vcpu_kick(vcpu);
> > > > +       }
> > > > +}
> > > This is too similar to kvm_irq_delivery_to_apic(). Why not reuse it. We
> > > can use one of reserved delivery modes as PV delivery mode. We will
> > > disallow guest to trigger it through apic interface, so this will not be
> > > part of ABI and can be changed at will.
[...]
> > kvm/x86.c
> > =========
> > kvm_pv_kick_cpu_op()
> > {
> >
> >   struct kvm_lapic_irq lapic_irq;
> >
> >   lapic_irq.shorthand = 0;
> >   lapic_irq.dest_mode = 0;
> >   lapic_irq.dest_id = apicid;
> >
> >   lapic_irq.delivery_mode = PV_DELIVERY_MODE;
> >   kvm_irq_delivery_to_apic(kvm, 0,&lapic_irq );
> >
> > }
> >
> > kvm/lapic.c
> > ==========
> > _apic_accept_irq()
> > {
> > ...
> > case APIC_DM_REMRD:
> >                  result = 1;
> >                  vcpu->pv_unhalted = 1
> >                  smp_mb();
> >                  kvm_make_request(KVM_REQ_EVENT, vcpu);
> >                  kvm_vcpu_kick(vcpu);
> >                  break;
> >
> > ...
> > }
> >
> > here using PV_DELIVERY_MODE = APIC_DM_REMRD, which was unused.
> Yes, this is what I mean except that PV_DELIVERY_MODE should be
> number defined as reserved by Intel spec.
Hi Gleb, Avi,

This had been TODO in my V8 patches.
I 'll fold this into V9 (while rebasing to
3.5-rc).
Please let me know if it is OK.


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