On Mon, Jan 08, 2024, Prasad Pandit wrote:
> On Wed, 3 Jan 2024 at 13:24, Prasad Pandit <ppandit@xxxxxxxxxx> wrote:
> > 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()")
> > Signed-off-by: Prasad Pandit <pjp@xxxxxxxxxxxxxxxxx>
> > ---
> > arch/x86/kvm/x86.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 1a3aaa7dafae..468870450b8b 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -5405,7 +5405,8 @@ 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);
> > --
> > 2.43.0
>
> Ping...!
This is on my list of things to grab for 6.8, I'm just waiting for various pull
requests to fully land in order to simplify my branch management.
