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
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