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Subject: Re: [PATCH v4 07/21] KVM: arm64: Support SDEI_EVENT_UNREGISTER
 hypercall
To:     Gavin Shan <gshan@redhat.com>, kvmarm@lists.cs.columbia.edu
Cc:     maz@kernel.org, linux-kernel@vger.kernel.org,
        Jonathan.Cameron@huawei.com, pbonzini@redhat.com, will@kernel.org
References: <20210815001352.81927-1-gshan@redhat.com>
 <20210815001352.81927-8-gshan@redhat.com>
From:   Eric Auger <eauger@redhat.com>
Message-ID: <100a4aa0-6c2d-2fec-6f11-c7e64946ef0b@redhat.com>
Date:   Tue, 9 Nov 2021 18:05:01 +0100
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On 8/15/21 2:13 AM, Gavin Shan wrote:
> This supports SDEI_EVENT_UNREGISTER hypercall. It's used by the
> guest to unregister SDEI event. The SDEI event won't be raised to
> the guest or specific vCPU after it's unregistered successfully.
> It's notable the SDEI event is disabled automatically on the guest
> or specific vCPU once it's unregistered successfully.
> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  arch/arm64/kvm/sdei.c | 61 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
> 
> diff --git a/arch/arm64/kvm/sdei.c b/arch/arm64/kvm/sdei.c
> index b4162efda470..a3ba69dc91cb 100644
> --- a/arch/arm64/kvm/sdei.c
> +++ b/arch/arm64/kvm/sdei.c
> @@ -308,6 +308,65 @@ static unsigned long kvm_sdei_hypercall_context(struct kvm_vcpu *vcpu)
>  	return ret;
>  }
>  
> +static unsigned long kvm_sdei_hypercall_unregister(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvm_sdei_kvm *ksdei = kvm->arch.sdei;
> +	struct kvm_sdei_vcpu *vsdei = vcpu->arch.sdei;
> +	struct kvm_sdei_event *kse = NULL;
> +	struct kvm_sdei_kvm_event *kske = NULL;
> +	unsigned long event_num = smccc_get_arg1(vcpu);
> +	int index = 0;
> +	unsigned long ret = SDEI_SUCCESS;
> +
> +	/* Sanity check */
> +	if (!(ksdei && vsdei)) {
> +		ret = SDEI_NOT_SUPPORTED;
> +		goto out;
> +	}
> +
> +	if (!kvm_sdei_is_valid_event_num(event_num)) {
> +		ret = SDEI_INVALID_PARAMETERS;
> +		goto out;
> +	}
> +
> +	/* Check if the KVM event exists */
> +	spin_lock(&ksdei->lock);
> +	kske = kvm_sdei_find_kvm_event(kvm, event_num);
> +	if (!kske) {
> +		ret = SDEI_INVALID_PARAMETERS;
> +		goto unlock;
> +	}
> +
> +	/* Check if there is pending events */
> +	if (kske->state.refcount) {
> +		ret = SDEI_PENDING;
don't you want to record the fact the unregistration is outstanding to
perform subsequent actions? Otherwise nothing will hapen when the
current executing handlers complete?
> +		goto unlock;
> +	}
> +
> +	/* Check if it has been registered */
> +	kse = kske->kse;
> +	index = (kse->state.type == SDEI_EVENT_TYPE_PRIVATE) ?
> +		vcpu->vcpu_idx : 0;
you could have an inline for the above as this is executed in many
functions. even including the code below.
> +	if (!kvm_sdei_is_registered(kske, index)) {
> +		ret = SDEI_DENIED;
> +		goto unlock;
> +	}
> +
> +	/* The event is disabled when it's unregistered */
> +	kvm_sdei_clear_enabled(kske, index);
> +	kvm_sdei_clear_registered(kske, index);
> +	if (kvm_sdei_empty_registered(kske)) {
a refcount mechanism would be cleaner I think.
> +		list_del(&kske->link);
> +		kfree(kske);
> +	}
> +
> +unlock:
> +	spin_unlock(&ksdei->lock);
> +out:
> +	return ret;
> +}
> +
>  int kvm_sdei_hypercall(struct kvm_vcpu *vcpu)
>  {
>  	u32 func = smccc_get_function(vcpu);
> @@ -333,6 +392,8 @@ int kvm_sdei_hypercall(struct kvm_vcpu *vcpu)
>  	case SDEI_1_0_FN_SDEI_EVENT_COMPLETE:
>  	case SDEI_1_0_FN_SDEI_EVENT_COMPLETE_AND_RESUME:
>  	case SDEI_1_0_FN_SDEI_EVENT_UNREGISTER:
> +		ret = kvm_sdei_hypercall_unregister(vcpu);
> +		break;
>  	case SDEI_1_0_FN_SDEI_EVENT_STATUS:
>  	case SDEI_1_0_FN_SDEI_EVENT_GET_INFO:
>  	case SDEI_1_0_FN_SDEI_EVENT_ROUTING_SET:
>