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    SubjectRe: [PATCH RFC V3 2/4] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks
    On 11/30/2011 10:59 AM, Raghavendra K T wrote:
    > Add a hypercall to KVM hypervisor to support pv-ticketlocks
    >
    > 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_KICK_VCPU/KVM_CAP_KICK_VCPU.
    >
    > Qemu needs a corresponding patch to pass up the presence of this feature to
    > guest via cpuid. Patch to qemu will be sent separately.
    >
    > There is no Xen/KVM hypercall interface to await kick from.

    The hypercall needs to be documented in
    Documentation/virtual/kvm/hypercalls.txt.

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

    > /* 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.

    >
    > /* 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.

    >
    > +/*
    > + * 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().

    > + 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.

    > + 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.

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

    --
    error compiling committee.c: too many arguments to function



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