Re: [PATCH 1/3] KVM: x86: make vendor code check for all nested events

[Sean Christopherson <seanjc@google.com>]

On Wed, Apr 27, 2022, Paolo Bonzini wrote:
> Right now, the VMX preemption timer is special cased via the
> hv_timer_pending, but the purpose of the callback can be easily
> extended to observing any event that can occur only in non-root
> mode.  Interrupts, NMIs etc. are already handled properly by
> the *_interrupt_allowed callbacks, so what is missing is only
> MTF.  Check it in the newly-renamed callback, so that
> kvm_vcpu_running's call to kvm_check_nested_events
> becomes redundant.
> 
> Cc: stable@vger.kernel.org
> Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 2 +-
>  arch/x86/kvm/vmx/nested.c       | 7 ++++++-
>  arch/x86/kvm/x86.c              | 8 ++++----
>  3 files changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4ff36610af6a..e2e4f60159e9 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1504,7 +1504,7 @@ struct kvm_x86_ops {
>  struct kvm_x86_nested_ops {
>  	void (*leave_nested)(struct kvm_vcpu *vcpu);
>  	int (*check_events)(struct kvm_vcpu *vcpu);
> -	bool (*hv_timer_pending)(struct kvm_vcpu *vcpu);
> +	bool (*has_events)(struct kvm_vcpu *vcpu);
>  	void (*triple_fault)(struct kvm_vcpu *vcpu);
>  	int (*get_state)(struct kvm_vcpu *vcpu,
>  			 struct kvm_nested_state __user *user_kvm_nested_state,
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 856c87563883..54672025c3a1 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3857,6 +3857,11 @@ static bool nested_vmx_preemption_timer_pending(struct kvm_vcpu *vcpu)
>  	       to_vmx(vcpu)->nested.preemption_timer_expired;
>  }
>  
> +static bool vmx_has_nested_events(struct kvm_vcpu *vcpu)
> +{
> +	return nested_vmx_preemption_timer_pending(vcpu) || vmx->nested.mtf_pending;

This doesn't even compile...

arch/x86/kvm/vmx/nested.c: In function ‘vmx_has_nested_events’:
arch/x86/kvm/vmx/nested.c:3862:61: error: ‘vmx’ undeclared (first use in this function)
 3862 |         return nested_vmx_preemption_timer_pending(vcpu) || vmx->nested.mtf_pending;
      |                                                             ^~~
arch/x86/kvm/vmx/nested.c:3862:61: note: each undeclared identifier is reported only once for each function it appears in
  CC [M]  arch/x86/kvm/svm/svm_onhyperv.o
arch/x86/kvm/vmx/nested.c:3863:1: error: control reaches end of non-void function [-Werror=return-type]
 3863 | }
      | ^
cc1: all warnings being treated as errors
  LD [M]  arch/x86/kvm/kvm.o