| Message ID | 1508916400-20228-1-git-send-email-ann.zhuangyanying@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 25/10/2017 09:26, Zhuangyanying wrote: > From: Xiangyou Xie <xiexiangyou@huawei.com> > > When the guest is using the pv-spinlock, and there is a race of vcpu1 decides to HALT and vcpu2 releasing the lock, the vcpu2 might fail to wake up vcpu1. > In the case of PV spinlock, the vcpu2 executes the following to wake up vcpu: > case APIC_DM_REMRD: > result = 1; > vcpu->arch.pv.pv_unhalted = 1; > kvm_make_request(KVM_REQ_EVENT, vcpu); > kvm_vcpu_kick(vcpu); > break; > Due to lack of smp_mb before kvm_vcpu_kick, the changes of pv_unhalted > and vcpu->requests may be delayed to be after the operation of kvm_vcpu_kick. Since Linux 4.7 (commit 2e4682ba2ed7, "KVM: add missing memory barrier in kvm_{make,check}_request", 2016-04-20), kvm_make_request has a smp_wmb(). However, even before that commit "set_bit" implicitly has a barrier on x86, so there is no effect from the patch below. Paolo > On the other part, if the vcpu1 is just to execute the prepare_to_wait, vcpu2's kvm_vcpu_kick will have no effect, but vcpu1 fails to pass the kvm_vcpu_check_block() and as a result get blocked. > for (;;) { > //------->when vcpu2 do the kvm_vcpu_kick, vcpu1 has not reached here > prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE); > > if (kvm_vcpu_check_block(vcpu) < 0) > break; > > waited = true; > schedule(); > } > > Adding an smp_mb() before vcpu2 doing the kvm_vcpu_kick works. > > Signed-off-by: Xiangyou Xie<xiexiangyou@huawei.com> > Signed-off-by: Liuxiaojian <liuxiaojian6@huawei.com> > --- > arch/x86/kvm/lapic.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 69c5612..d37c0fd 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -987,6 +987,7 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode, > result = 1; > vcpu->arch.pv.pv_unhalted = 1; > kvm_make_request(KVM_REQ_EVENT, vcpu); > + smp_mb(); > kvm_vcpu_kick(vcpu); > break; > >
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 69c5612..d37c0fd 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -987,6 +987,7 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode, result = 1; vcpu->arch.pv.pv_unhalted = 1; kvm_make_request(KVM_REQ_EVENT, vcpu); + smp_mb(); kvm_vcpu_kick(vcpu); break;