On 01/14/2011 10:03 AM, Rik van Riel wrote:
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. 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;
NULL
@@ -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); + }
This is subject to the same race as before. If another vcpu picks up vcpu->pid before the assignment (that is, oldpid), but dereferences it after put_pid(), it hits freed memory.
You want something like struct pid *oldpid = vcpu->pid; rcu_assign_pointer(vcpu->pid, get_task_pid()); synchronize_rcu(); put_pid(oldpid); with rcu_read_lock() / rcu_dereference() protection on the reader side. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html