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 <haozhong.zhang@intel.com>
Reported-by: "Ramamurthy, Venkatesh" <venkatesh.ramamurthy@intel.com>
Reported-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Fixes: 28b835d60fcc ("KVM: Update Posted-Interrupts Descriptor when vCPU is preempted")
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

1 files changed, 1 insertions, 5 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 06c0c6d0541e..7328c8c0ea3b 100644
--- a/arch/x86/kvm/vmx.c
+++ b/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",