Re: [PATCH v4 07/21] KVM: arm64: Support SDEI_EVENT_UNREGISTER hypercall

[Gavin Shan]

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@xxxxxxxxxx>
> > ---
> >   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