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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>
 <100a4aa0-6c2d-2fec-6f11-c7e64946ef0b@redhat.com>
 <11022feb-16d7-8732-0d3a-12a65a4e39de@redhat.com>
From:   Eric Auger <eauger@redhat.com>
Message-ID: <60e5b475-2ebb-f697-9024-3afba7a7ab3e@redhat.com>
Date:   Tue, 25 Jan 2022 19:42:56 +0100
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Hi Gavin,
On 1/12/22 3:38 AM, Gavin Shan wrote:
> 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@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?>
> It's not necessary. The guest should retry in this case.

I do not understand that from the spec:
6.7 Unregistering an event says

With the PENDING status, the unregister request will be queued until the
event is completed using SDEI_EVENT_COMPLETE .

Also there is state called "Handler-unregister-pending"

But well I would need to dig further into the spec again :)


> 
>>> +        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.

I don't get why you can't increment/decrement the ref count each time
the event is registered/unregistered by a given vcpu to manage its life
cycle? Does not mean you don't need the bitmap to know the actual mapping.

Thanks

Eric
> 
>>> +        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
>