Re: [PATCH v2 6/9] KVM: x86: make vendor code check for all nested events

Maxim Levitsky
2022-08-17T14:11:28Z

On Thu, 2022-08-11 at 17:06 -0400, Paolo Bonzini wrote:
> Interrupts, NMIs etc. sent while in guest mode are already handled
> properly by the *_interrupt_allowed callbacks, but other events can
> cause a vCPU to be runnable that are specific to guest mode.
>
> In the case of VMX there are two, the preemption timer and the
> monitor trap.  The VMX preemption timer is already special cased via
> the hv_timer_pending callback, but the purpose of the callback can be
> easily extended to MTF or in fact any other event that can occur only
> in guest mode.

I am just curious, can this happen with MTF? I see that 'vmx->nested.mtf_pending'
is only set from 'vmx_update_emulated_instruction' and that should only
in turn be called when we emulate an instruction, which implies that the
guest is not halted.

>
> Rename the callback and add an MTF check; kvm_arch_vcpu_runnable()
> now will return true if an MTF is pending, without relying on
> kvm_vcpu_running()'s call to kvm_check_nested_events().  Until that call
> is removed, however, the patch introduces no functional change.
>
> Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
> Reviewed-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       | 9 ++++++++-
>  arch/x86/kvm/x86.c              | 8 ++++----
>  3 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 5ffa578cafe1..293ff678fff5 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1636,7 +1636,7 @@ struct kvm_x86_nested_ops {
>         int (*check_events)(struct kvm_vcpu *vcpu);
>         bool (*handle_page_fault_workaround)(struct kvm_vcpu *vcpu,
>                                              struct x86_exception *fault);
> -       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 ddd4367d4826..9631cdcdd058 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3876,6 +3876,13 @@ 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)
> +{
> +       struct vcpu_vmx *vmx = to_vmx(vcpu);
> +
> +       return nested_vmx_preemption_timer_pending(vcpu) || vmx->nested.mtf_pending;
> +}
> +
>  static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
>  {
>         struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -6816,7 +6823,7 @@ struct kvm_x86_nested_ops vmx_nested_ops = {
>         .leave_nested = vmx_leave_nested,
>         .check_events = vmx_check_nested_events,
>         .handle_page_fault_workaround = nested_vmx_handle_page_fault_workaround,
> -       .hv_timer_pending = nested_vmx_preemption_timer_pending,
> +       .has_events = vmx_has_nested_events,
>         .triple_fault = nested_vmx_triple_fault,
>         .get_state = vmx_get_nested_state,
>         .set_state = vmx_set_nested_state,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7f084613fac8..0f9f24793b8a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9789,8 +9789,8 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool *req_immediate_exit)
>         }
>
>         if (is_guest_mode(vcpu) &&
> -           kvm_x86_ops.nested_ops->hv_timer_pending &&
> -           kvm_x86_ops.nested_ops->hv_timer_pending(vcpu))
> +           kvm_x86_ops.nested_ops->has_events &&
> +           kvm_x86_ops.nested_ops->has_events(vcpu))
>                 *req_immediate_exit = true;
>
>         WARN_ON(vcpu->arch.exception.pending);
> @@ -12562,8 +12562,8 @@ static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
>                 return true;
>
>         if (is_guest_mode(vcpu) &&
> -           kvm_x86_ops.nested_ops->hv_timer_pending &&
> -           kvm_x86_ops.nested_ops->hv_timer_pending(vcpu))
> +           kvm_x86_ops.nested_ops->has_events &&
> +           kvm_x86_ops.nested_ops->has_events(vcpu))
>                 return true;
>
>         if (kvm_xen_has_pending_events(vcpu))

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky