KVM: track pid for VCPU only on KVM_RUN ioctl
We currently track the pid of the task that runs the VCPU in vcpu_load.
If a yield to that VCPU is triggered while the PID of the wrong thread
is active, the wrong thread might receive a yield, but this will most
likely not help the executing thread at all. Instead, if we only track
the pid on the KVM_RUN ioctl, there are two possibilities:
1) the thread that did a non-KVM_RUN ioctl is holding a mutex that
the VCPU thread is waiting for. In this case, the VCPU thread is not
runnable, but we also do not do a wrong yield.
2) the thread that did a non-KVM_RUN ioctl is sleeping, or doing
something that does not block the VCPU thread. In this case, the
VCPU thread can receive the directed yield correctly.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
CC: Rik van Riel <riel@redhat.com>
CC: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
CC: Michael Mueller <mimu@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2ffee30..c5c186a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -124,15 +124,6 @@
if (mutex_lock_killable(&vcpu->mutex))
return -EINTR;
- 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);
- if (oldpid)
- synchronize_rcu();
- put_pid(oldpid);
- }
cpu = get_cpu();
preempt_notifier_register(&vcpu->preempt_notifier);
kvm_arch_vcpu_load(vcpu, cpu);
@@ -2050,6 +2041,15 @@
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;
+ struct pid *newpid = get_task_pid(current, PIDTYPE_PID);
+ rcu_assign_pointer(vcpu->pid, newpid);
+ if (oldpid)
+ synchronize_rcu();
+ put_pid(oldpid);
+ }
r = kvm_arch_vcpu_ioctl_run(vcpu, vcpu->run);
trace_kvm_userspace_exit(vcpu->run->exit_reason, r);
break;