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    SubjectRe: [PATCH RFC V2 3/5] kvm hypervisor : Add two hypercalls to support pv-ticketlock
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    On Mon, 2011-10-24 at 00:35 +0530, Raghavendra K T wrote:
    > Add two hypercalls to KVM hypervisor to support pv-ticketlocks.
    >
    > KVM_HC_WAIT_FOR_KICK blocks the calling vcpu until another vcpu kicks it or it
    > is woken up because of an event like interrupt.
    >
    > KVM_HC_KICK_CPU allows the calling vcpu to kick another vcpu.
    >
    > The presence of these hypercalls is indicated to guest via
    > KVM_FEATURE_WAIT_FOR_KICK/KVM_CAP_WAIT_FOR_KICK.
    >
    > 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.
    >
    > Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
    > Signed-off-by: Suzuki Poulose <suzuki@in.ibm.com>
    > Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
    > ---
    > diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
    > index 734c376..2874c19 100644
    > --- a/arch/x86/include/asm/kvm_para.h
    > +++ b/arch/x86/include/asm/kvm_para.h
    > @@ -16,12 +16,14 @@
    > #define KVM_FEATURE_CLOCKSOURCE 0
    > #define KVM_FEATURE_NOP_IO_DELAY 1
    > #define KVM_FEATURE_MMU_OP 2
    > +
    > /* 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_WAIT_FOR_KICK 6
    >
    > /* 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 84a28ea..b43fd18 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -2077,6 +2077,7 @@ 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_WAIT_FOR_KICK:
    > r = 1;
    > break;
    > case KVM_CAP_COALESCED_MMIO:
    > @@ -2548,7 +2549,8 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
    > (1 << KVM_FEATURE_NOP_IO_DELAY) |
    > (1 << KVM_FEATURE_CLOCKSOURCE2) |
    > (1 << KVM_FEATURE_ASYNC_PF) |
    > - (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
    > + (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
    > + (1 << KVM_FEATURE_WAIT_FOR_KICK);
    >
    > if (sched_info_on())
    > entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
    > @@ -5231,6 +5233,61 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
    > return 1;
    > }
    >
    > +/*
    > + * kvm_pv_wait_for_kick_op : Block until kicked by either a KVM_HC_KICK_CPU
    > + * hypercall or a event like interrupt.
    > + *
    > + * @vcpu : vcpu which is blocking.
    > + */
    > +static void kvm_pv_wait_for_kick_op(struct kvm_vcpu *vcpu)
    > +{
    > + DEFINE_WAIT(wait);
    > +
    > + /*
    > + * Blocking on vcpu->wq allows us to wake up sooner if required to
    > + * service pending events (like interrupts).
    > + *
    > + * Also set state to TASK_INTERRUPTIBLE before checking vcpu->kicked to
    > + * avoid racing with kvm_pv_kick_cpu_op().
    > + */
    > + prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
    > +
    > + /*
    > + * Somebody has already tried kicking us. Acknowledge that
    > + * and terminate the wait.
    > + */
    > + if (vcpu->kicked) {
    > + vcpu->kicked = 0;
    > + goto end_wait;
    > + }
    > +
    > + /* Let's wait for either KVM_HC_KICK_CPU or someother event
    > + * to wake us up.
    > + */
    > +
    > + srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
    > + schedule();
    > + vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
    > +
    > +end_wait:
    > + finish_wait(&vcpu->wq, &wait);
    > +}
    > +
    > +/*
    > + * 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);
    > +
    > + if (vcpu) {
    > + vcpu->kicked = 1;

    I'm not sure about it, but maybe we want a memory barrier over here?

    > + wake_up_interruptible(&vcpu->wq);
    > + }
    > +}
    --

    Sasha.



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