linux-kernel - Re: [PATCH v4 07/21] KVM: arm64: Support SDEI_EVENT

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Date:   Wed, 12 Jan 2022 10:38:56 +0800
From:   Gavin Shan <gshan@...hat.com>
To:     Eric Auger <eauger@...hat.com>, kvmarm@...ts.cs.columbia.edu
Cc:     maz@...nel.org, linux-kernel@...r.kernel.org,
        Jonathan.Cameron@...wei.com, pbonzini@...hat.com, will@...nel.org
Subject: Re: [PATCH v4 07/21] KVM: arm64: Support SDEI_EVENT_UNREGISTER
 hypercall

Hi Eric,

On 11/10/21 1:05 AM, Eric Auger wrote:
> 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@...hat.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?

It's not necessary. The guest should retry in this case.

>> +		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.

Ok, it's a good idea.

>> +	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.

A refcount isn't working well. We need a mapping here because the private
SDEI event can be enabled/registered on multiple vCPUs. We need to know
the exact vCPUs where the private SDEI event is enabled/registered.

>> +		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:
>>

Thanks,
Gavin