KVM: VMX: do not change SN bit in vmx_update_pi_irte()

In kvm_vcpu_trigger_posted_interrupt() and pi_pre_block(), KVM
assumes that PI notification events should not be suppressed when the
target vCPU is not blocked.

vmx_update_pi_irte() sets the SN field before changing an interrupt
from posting to remapping, but it does not check the vCPU mode.
Therefore, the change of SN field may break above the assumption.
Besides, I don't see reasons to suppress notification events here, so
remove the changes of SN field to avoid race condition.

Signed-off-by: Haozhong Zhang <[email protected]>
Reported-by: "Ramamurthy, Venkatesh" <[email protected]>
Reported-by: Dan Williams <[email protected]>
Reviewed-by: Paolo Bonzini <[email protected]>
Fixes: 28b835d ("KVM: Update Posted-Interrupts Descriptor when vCPU is preempted")
Signed-off-by: Radim Krčmář <[email protected]>

Author: Haozhong Zhang

arch/x86/kvm/vmx.c

@@ -11911,12 +11911,8 @@ static int vmx_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
 
 		if (set)
 			ret = irq_set_vcpu_affinity(host_irq, &vcpu_info);
-		else {
-			/* suppress notification event before unposting */
-			pi_set_sn(vcpu_to_pi_desc(vcpu));
+		else
 			ret = irq_set_vcpu_affinity(host_irq, NULL);
-			pi_clear_sn(vcpu_to_pi_desc(vcpu));
-		}
 
 		if (ret < 0) {
 			printk(KERN_INFO "%s: failed to update PI IRTE\n",