Patch "KVM: VMX: do not change SN bit in vmx_update_pi_irte()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-vmx-do-not-change-sn-bit-in-vmx_update_pi_irte.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Haozhong Zhang <[email protected]>
Date: Mon, 18 Sep 2017 09:56:49 +0800
Subject: KVM: VMX: do not change SN bit in vmx_update_pi_irte()
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From: Haozhong Zhang <[email protected]>

commit dc91f2eb1a4021eb6705c15e474942f84ab9b211 upstream.

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.

---
 arch/x86/kvm/vmx.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

@@ -11215,12 +11215,8 @@ static int vmx_update_pi_irte(struct kvm
 
 		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",

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/kvm-vmx-do-not-change-sn-bit-in-vmx_update_pi_irte.patch queue-4.9/kvm-vmx-remove-warn_on_once-in-kvm_vcpu_trigger_posted_interrupt.patch