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>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 002fe0b12c9..bc8bfd15ab7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -137,6 +137,14 @@ void vcpu_load(struct kvm_vcpu *vcpu)
         int cpu;
 
         mutex_lock(&vcpu->mutex);
+        if (unlikely(vcpu->pid != current->pids[PIDTYPE_PID].pid)) {
+                /* The thread running this VCPU changed. */
+                struct pid *oldpid = vcpu->pid;
+                struct pid *newpid = get_task_pid(current, PIDTYPE_PID);
+                rcu_assign_pointer(vcpu->pid, newpid);
+                synchronize_rcu();
+                put_pid(oldpid);
+        }
         cpu = get_cpu();
         preempt_notifier_register(&vcpu->preempt_notifier);
         kvm_arch_vcpu_load(vcpu, cpu);
@@ -212,6 +220,7 @@ 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 = NULL;
         init_waitqueue_head(&vcpu->wq);
         kvm_async_pf_vcpu_init(vcpu);
 
@@ -236,6 +245,7 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_init);
 
 void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
 {
+        put_pid(vcpu->pid);
         kvm_arch_vcpu_uninit(vcpu);
         free_page((unsigned long)vcpu->run);
 }