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Subject[RFC -v6 PATCH 7/8] 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..86c4905 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 = NULL;
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 +1459,14 @@ 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;
+ struct pid *newpid = get_task_pid(current, PIDTYPE_PID);
+ rcu_assign_pointer(vcpu->pid, newpid);
+ synchronize_rcu();
+ put_pid(oldpid);
+ }
r = kvm_arch_vcpu_ioctl_run(vcpu, vcpu->run);
break;
case KVM_GET_REGS: {


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