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    Subject[RFC -v5 PATCH 1/4] kvm: keep track of which task is running a KVM vcpu
    Keep track of which task is running a KVM vcpu.  This helps us
    figure out later what task to wake up if we want to boost a
    vcpu that got preempted.

    Unfortunately there are no guarantees that the same task
    always keeps the same vcpu, so we can only track the task
    across a single "run" of the vcpu.

    Signed-off-by: Rik van Riel <riel@redhat.com>

    diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
    index a055742..9d56ed5 100644
    --- a/include/linux/kvm_host.h
    +++ b/include/linux/kvm_host.h
    @@ -81,6 +81,7 @@ struct kvm_vcpu {
    #endif
    int vcpu_id;
    struct mutex mutex;
    + struct pid *pid;
    int cpu;
    atomic_t guest_mode;
    struct kvm_run *run;
    diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    index 5225052..65e997a 100644
    --- a/virt/kvm/kvm_main.c
    +++ b/virt/kvm/kvm_main.c
    @@ -185,6 +185,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
    vcpu->cpu = -1;
    vcpu->kvm = kvm;
    vcpu->vcpu_id = id;
    + vcpu->pid = 0;
    init_waitqueue_head(&vcpu->wq);

    page = alloc_page(GFP_KERNEL | __GFP_ZERO);
    @@ -208,6 +209,8 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_init);

    void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
    {
    + if (vcpu->pid)
    + put_pid(vcpu->pid);
    kvm_arch_vcpu_uninit(vcpu);
    free_page((unsigned long)vcpu->run);
    }
    @@ -1456,6 +1459,12 @@ static long kvm_vcpu_ioctl(struct file *filp,
    r = -EINVAL;
    if (arg)
    goto out;
    + if (unlikely(vcpu->pid != current->pids[PIDTYPE_PID].pid)) {
    + /* The thread running this VCPU changed. */
    + struct pid *oldpid = vcpu->pid;
    + vcpu->pid = get_task_pid(current, PIDTYPE_PID);
    + put_pid(oldpid);
    + }
    r = kvm_arch_vcpu_ioctl_run(vcpu, vcpu->run);
    break;
    case KVM_GET_REGS: {


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