On 10/23/2011 09:05 PM, 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.
>
>
> +/*
> + * 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);
> +}
This hypercall can be replaced by a HLT instruction, no?
I'm pretty sure this misses a lot of stuff from kvm_vcpu_block().
> +
> +/*
> + * 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);
> +
Is the vcpu number meaningful? We should reuse an existing identifier
like the APIC ID.
> + if (vcpu) {
> + vcpu->kicked = 1;
Need to use smp memory barriers here.
> + wake_up_interruptible(&vcpu->wq);
> + }
> +}
> +
> int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
> {
> unsigned long nr, a0, a1, a2, a3, ret;
>
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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