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...!
---
- Prasad
