[PATCH] KVM: SVM: unconditionally wake up VCPU on IOMMU interrupt

Paolo Bonzini
2017-10-10T10:57:29Z

Checking the mode is unnecessary, and is done without a memory barrier
separating the LAPIC write from the vcpu->mode read; in addition,
kvm_vcpu_wake_up is already doing a check for waiters on the wait queue
that has the same effect.

In practice it's safe because spin_lock has full-barrier semantics on x86,
but don't be too clever.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/svm.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 01e6e8fab5d6..712406f725a2 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1034,15 +1034,12 @@ static int avic_ga_log_notifier(u32 ga_tag)
}
spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);

- if (!vcpu)
- return 0;
-
/* Note:
* At this point, the IOMMU should have already set the pending
* bit in the vAPIC backing page. So, we just need to schedule
* in the vcpu.
*/
- if (vcpu->mode == OUTSIDE_GUEST_MODE)
+ if (vcpu)
kvm_vcpu_wake_up(vcpu);

return 0;
--
1.8.3.1