Re: [PATCH RFC V3 2/4] kvm hypervisor : Add a hypercall to KVM hypervisorto support pv-ticketlocks

[Raghavendra K T]

[ CCing Jeremy's new email ID ]
Hi Avi,
Thanks for review and inputs.

On 12/01/2011 04:41 PM, Avi Kivity wrote:
> On 11/30/2011 10:59 AM, Raghavendra K T wrote:
>
> The hypercall needs to be documented in
> Documentation/virtual/kvm/hypercalls.txt.

Yes, Sure 'll document.  hypercalls.txt is a new file right?. also I 
have to document APIs in Documentation/virtual/kvm/api.txt.

> Have you tested it on AMD machines?  There are some differences in the
> hypercall infrastructure there.

Yes. 'll test on AMD machine and update on that.

> >   /* This indicates that the new set of kvmclock msrs
> >    * are available. The use of 0x11 and 0x12 is deprecated
> >    */
> >   #define KVM_FEATURE_CLOCKSOURCE2        3
> >   #define KVM_FEATURE_ASYNC_PF		4
> >   #define KVM_FEATURE_STEAL_TIME		5
> > +#define KVM_FEATURE_KICK_VCPU		6
>
> Documentation/virtual/kvm/cpuid.txt.

Yes. 'll do that.

> >   /* The last 8 bits are used to indicate how to interpret the flags field
> >    * in pvclock structure. If no bits are set, all flags are ignored.
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index c38efd7..6e1c8b4 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2103,6 +2103,7 @@ int kvm_dev_ioctl_check_extension(long ext)
> >   	case KVM_CAP_XSAVE:
> >   	case KVM_CAP_ASYNC_PF:
> >   	case KVM_CAP_GET_TSC_KHZ:
> > +	case KVM_CAP_KICK_VCPU:
>
> This is redundant with the feature bit?  In general, KVM_CAP is for the
> host API, while KVM_FEATURE is for the guest API.

No its not. I have to check the flow again. I understood that this 
completes the guest querying, that checks for KVM_FEATURE availability.
Did I miss something? I need a little deep dive though.

> > +/*
> > + * kvm_pv_kick_cpu_op:  Kick a vcpu.
> > + *
> > + * @cpu - vcpu to be kicked.
> > + */
> > +static void kvm_pv_kick_cpu_op(struct kvm *kvm, int cpu)
> > +{
> > +	struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, cpu);
>
> There is no guarantee that guest cpu numbers match host vcpu numbers.
> Use APIC IDs, and kvm_apic_match_dest().

Okay. I have to dig more on this.

> > +	struct kvm_mp_state mp_state;
> > +
> > +	mp_state.mp_state = KVM_MP_STATE_RUNNABLE;
> > +	if (vcpu) {
> > +		vcpu->kicked = 1;
> > +		/* Ensure kicked is always set before wakeup */
> > +		barrier();
> > +	}
> > +	kvm_arch_vcpu_ioctl_set_mpstate(vcpu,&mp_state);
>
> This must only be called from the vcpu thread.

Hmm. Okay. 'll check this.

> > +	kvm_vcpu_kick(vcpu);
> > +}
> > +
> >
> >   	struct kvm_vcpu_arch arch;
> > +
> > +	/*
> > +	 * blocked vcpu wakes up by checking this flag set by unlocker.
> > +	 */
> > +	int kicked;
>
> Write only variable.

Yes 'll remove comments.

> An alternative approach is to use an MSR protocol like x2apic ICR.

'll explore on this too.

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