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: bdedff263132 ("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>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 363b1c08020578b090b53d74482d9c8912629ec9..25bc52cdf8f452c6814986b157d1cf55cb193252 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5454,7 +5454,8 @@ 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);