From 7a72f7a140bfd3a5dae73088947010bfdbcf6a40 Mon Sep 17 00:00:00 2001 From: Christian Borntraeger Date: Tue, 5 Aug 2014 16:44:14 +0200 Subject: 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 CC: Rik van Riel CC: Raghavendra K T CC: Michael Mueller Signed-off-by: Paolo Bonzini --- virt/kvm/kvm_main.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) (limited to 'virt') 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 @@ int vcpu_load(struct kvm_vcpu *vcpu) 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 @@ 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); + 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; -- cgit v1.1