Merge: KVM: x86: make KVM_REQ_NMI request iff NMI pending for vcpu

MR: https://gitlab.com/redhat/rhel/src/kernel/rhel-9/-/merge_requests/1338

JIRA: https://issues.redhat.com/browse/RHEL-2815

commit 6231c9e
Author: Prasad Pandit <pjp@fedoraproject.org>
Date:   Wed Jan 3 13:23:43 2024 +0530

    KVM: x86: make KVM_REQ_NMI request iff NMI pending for vcpu

    kvm_vcpu_ioctl_x86_set_vcpu_events() routine makes 'KVM_REQ_NMI'
    request for a vcpu even when its 'events->nmi.pending' is zero.
    Ex:
        qemu_thread_start
         kvm_vcpu_thread_fn
          qemu_wait_io_event
           qemu_wait_io_event_common
            process_queued_cpu_work
             do_kvm_cpu_synchronize_post_init/_reset
              kvm_arch_put_registers
               kvm_put_vcpu_events (cpu, level=[2|3])

    This leads vCPU threads in QEMU to constantly acquire & release the
    global mutex lock, delaying the guest boot due to lock contention.
    Add check to make KVM_REQ_NMI request only if vcpu has NMI pending.

    Fixes: bdedff2 ("KVM: x86: Route pending NMIs from userspace through process_nmi()")
    Cc: stable@vger.kernel.org
    Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
    Link: https://lore.kernel.org/r/20240103075343.549293-1-ppandit@redhat.com
    Signed-off-by: Sean Christopherson <seanjc@google.com>

Closes RHEL-2815
Signed-off-by: Prasad Pandit <ppandit@redhat.com>

Approved-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Approved-by: Marcelo Tosatti <mtosatti@redhat.com>

Merged-by: Scott Weaver <scweaver@redhat.com>

Author: swvrrh

arch/x86/kvm/x86.c

@@ -5402,7 +5402,8 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
 	if (events->flags & KVM_VCPUEVENT_VALID_NMI_PENDING) {
 		vcpu->arch.nmi_pending = 0;
 		atomic_set(&vcpu->arch.nmi_queued, events->nmi.pending);
-		kvm_make_request(KVM_REQ_NMI, vcpu);
+		if (events->nmi.pending)
+			kvm_make_request(KVM_REQ_NMI, vcpu);
 	}
 	static_call(kvm_x86_set_nmi_mask)(vcpu, events->nmi.masked);