path: root/virt
diff options
authorDavid Hildenbrand <dahi@linux.vnet.ibm.com>2014-11-25 17:04:08 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2014-12-04 15:29:12 +0100
commiteed6e79d7362335967def243cc891179a9c59892 (patch)
treeb1c803f19ad0c2a987c260977e8e670ff84205a2 /virt
parent9c1a5d38780e652275aa55362dbee0d7e827e069 (diff)
KVM: don't check for PF_VCPU when yielding
kvm_enter_guest() has to be called with preemption disabled and will set PF_VCPU. Current code takes PF_VCPU as a hint that the VCPU thread is running and therefore needs no yield. However, the check on PF_VCPU is wrong on s390, where preemption has to stay enabled in order to correctly process page faults. Thus, s390 reenables preemption and starts to execute the guest. The thread might be scheduled out between kvm_enter_guest() and kvm_exit_guest(), resulting in PF_VCPU being set but not being run. When this happens, the opportunity for directed yield is missed. However, this check is done already in kvm_vcpu_on_spin before calling kvm_vcpu_yield_loop: if (!ACCESS_ONCE(vcpu->preempted)) continue; so the check on PF_VCPU is superfluous in general, and this patch removes it. Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt')
1 files changed, 0 insertions, 4 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 759af6596a0..2ffee3018a3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1788,10 +1788,6 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target)
if (!task)
return ret;
- if (task->flags & PF_VCPU) {
- put_task_struct(task);
- return ret;
- }
ret = yield_to(task, 1);