linux-kernel - Re: [RFC PATCH v4 5/7] KVM: x86: add vCPU scoped toggling for disabled exits

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Date:   Wed, 20 Jul 2022 18:41:42 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Kechen Lu <kechenl@...dia.com>
Cc:     kvm@...r.kernel.org, pbonzini@...hat.com, chao.gao@...el.com,
        vkuznets@...hat.com, somduttar@...dia.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v4 5/7] KVM: x86: add vCPU scoped toggling for
 disabled exits

On Tue, Jun 21, 2022, Kechen Lu wrote:
> @@ -5980,6 +5987,8 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_event,
>  int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>  			    struct kvm_enable_cap *cap)
>  {
> +	struct kvm_vcpu *vcpu;
> +	unsigned long i;
>  	int r;
>  
>  	if (cap->flags)
> @@ -6036,14 +6045,17 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>  			break;
>  
>  		mutex_lock(&kvm->lock);
> -		if (kvm->created_vcpus)
> -			goto disable_exits_unlock;
> +		if (kvm->created_vcpus) {

I retract my comment about using a request, I got ahead of myself.

Don't update vCPUs, the whole point of adding the !kvm->created_vcpus check was
to avoid having to update vCPUs when the per-VM behavior changed.

In other words, keep the restriction and drop the request.

> +			kvm_for_each_vcpu(i, vcpu, kvm) {
> +				kvm_ioctl_disable_exits(vcpu->arch, cap->args[0]);
> +				kvm_make_request(KVM_REQ_DISABLE_EXITS, vcpu);
> +			}
> +		}
> +		mutex_unlock(&kvm->lock);
>  
>  		kvm_ioctl_disable_exits(kvm->arch, cap->args[0]);
>  
>  		r = 0;
> -disable_exits_unlock:
> -		mutex_unlock(&kvm->lock);
>  		break;
>  	case KVM_CAP_MSR_PLATFORM_INFO:
>  		kvm->arch.guest_can_read_msr_platform_info = cap->args[0];
> @@ -10175,6 +10187,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  
>  		if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
>  			static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
> +
> +		if (kvm_check_request(KVM_REQ_DISABLE_EXITS, vcpu))
> +			static_call(kvm_x86_update_disabled_exits)(vcpu);
>  	}
>  
>  	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win ||
> -- 
> 2.32.0
>