Re: [Qemu-devel] [PATCH v2] KVM: x86: Fix nmi injection failure when vcpu got blocked

[Paolo Bonzini <pbonzini@redhat.com>]

On 25/05/2017 08:56, Zhuangyanying wrote:
> From: ZhuangYanying <ann.zhuangyanying@huawei.com>
> 
> When spin_lock_irqsave() deadlock occurs inside the guest, vcpu threads,
> other than the lock-holding one, would enter into S state because of
> pvspinlock. Then inject NMI via libvirt API "inject-nmi", the NMI could
> not be injected into vm.
> 
> The reason is:
> 1 It sets nmi_queued to 1 when calling ioctl KVM_NMI in qemu, and sets
> cpu->kvm_vcpu_dirty to true in do_inject_external_nmi() meanwhile.
> 2 It sets nmi_queued to 0 in process_nmi(), before entering guest, because
> cpu->kvm_vcpu_dirty is true.
> 
> It's not enough just to check nmi_queued to decide whether to stay in
> vcpu_block() or not. NMI should be injected immediately at any situation.
> Add checking KVM_REQ_NMI request plus with nmi_queued in
> vm_vcpu_has_events().
> 
> Signed-off-by: Zhuang Yanying <ann.zhuangyanying@huawei.com>
> ---
>  arch/x86/kvm/x86.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 02363e3..2d15708 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8394,7 +8394,9 @@ static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
>  	if (vcpu->arch.pv.pv_unhalted)
>  		return true;
>  
> -	if (atomic_read(&vcpu->arch.nmi_queued))
> +	if ((kvm_test_request(KVM_REQ_NMI, vcpu) ||
> +	    atomic_read(&vcpu->arch.nmi_queued)) &&
> +	    kvm_x86_ops->nmi_allowed(vcpu))

It's the other way round; nmi_pending was correct in your v1.

Testing KVM_REQ_NMI replaces nmi_queued, while the bugfix tests
"vcpu->arch.nmi_pending && kvm_x86_ops->nmi_allowed(vcpu)".  The new est
has to match the existing test in inject_pending_event.

In fact, we also need to do the same change for SMIs, i.e.

	kvm_test_request(KVM_REQ_SMI, vcpu) ||
	(vcpu->arch.smi_pending && !is_smm(vcpu))

Thanks,

Paolo

>  		return true;
>  
>  	if (kvm_test_request(KVM_REQ_SMI, vcpu))
>