Re: [PATCH 4/4] KVM: VMX: Register posted interrupt wakeup handler iff APICv is enabled

[Paolo Bonzini]

On 09/10/21 02:11, Sean Christopherson wrote:
> Don't bother registering a posted interrupt wakeup handler if APICv is
> disabled, KVM utilizes the wakeup vector if and only if APICv is enabled.
> Practically speaking, there's no meaningful functional change as KVM's
> wakeup handler is a glorified nop if there are no vCPUs using posted
> interrupts, not to mention that nothing in the system should be sending
> wakeup interrupts when APICv is disabled.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>   arch/x86/kvm/vmx/vmx.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 9164f1870d49..df9ad4675215 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7553,7 +7553,8 @@ static void vmx_migrate_timers(struct kvm_vcpu *vcpu)
>   
>   static void hardware_unsetup(void)
>   {
> -	kvm_unregister_posted_intr_wakeup_handler(pi_wakeup_handler);
> +	if (enable_apicv)
> +		kvm_unregister_posted_intr_wakeup_handler(pi_wakeup_handler);
>   
>   	if (nested)
>   		nested_vmx_hardware_unsetup();
> @@ -7907,7 +7908,8 @@ static __init int hardware_setup(void)
>   	if (r)
>   		nested_vmx_hardware_unsetup();
>   
> -	kvm_register_posted_intr_wakeup_handler(pi_wakeup_handler);
> +	if (enable_apicv)
> +		kvm_register_posted_intr_wakeup_handler(pi_wakeup_handler);
>   
>   	return r;
>   }

Also adds unnecessary complexity (you have to ensure the condition 
cannot change from one call to the other), so I am only queuing patches 
1 and 2.

Paolo