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    SubjectRe: [PATCH 4/5] KVM: cpu hotplug support

    * Andrew Morton <akpm@osdl.org> wrote:

    > On Tue, 30 Jan 2007 14:56:16 -0000
    > Avi Kivity <avi@qumranet.com> wrote:
    >
    > > +static void decache_vcpus_on_cpu(int cpu)
    > > +{
    > > + struct kvm *vm;
    > > + struct kvm_vcpu *vcpu;
    > > + int i;
    > > +
    > > + spin_lock(&kvm_lock);
    > > + list_for_each_entry(vm, &vm_list, vm_list)
    > > + for (i = 0; i < KVM_MAX_VCPUS; ++i) {
    > > + vcpu = &vm->vcpus[i];
    > > + /*
    > > + * If the vcpu is locked, then it is running on some
    > > + * other cpu and therefore it is not cached on the
    > > + * cpu in question.
    > > + *
    > > + * If it's not locked, check the last cpu it executed
    > > + * on.
    > > + */
    > > + if (mutex_trylock(&vcpu->mutex)) {
    > > + if (vcpu->cpu == cpu) {
    > > + kvm_arch_ops->vcpu_decache(vcpu);
    > > + vcpu->cpu = -1;
    > > + }
    > > + mutex_unlock(&vcpu->mutex);
    > > + }
    > > + }
    > > + spin_unlock(&kvm_lock);
    > > +}
    >
    > The trylock is unpleasing. Perhaps kvm_lock should be a mutex or
    > something?

    this is a special case. The vcpu->mutex acts as a 'this vcpu is running
    right now' flag as well - hence the trylock signals: is it running right
    now or not - if it's not running we do not have to 'decache' it. But i
    agree and i already suggested to Avi to change kvm_lock to be a mutex -
    but this wont change the trylock.

    Ingo
    -
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