Re: [PATCH v6 04/18] KVM: arm64: Support SDEI_EVENT_REGISTER hypercall

[Gavin Shan]

Hi Oliver,

On 4/30/22 10:54 PM, Oliver Upton wrote:
> On Sun, Apr 03, 2022 at 11:38:57PM +0800, Gavin Shan wrote:
> > This supports SDEI_EVENT_REGISTER hypercall, which is used by guest
> > to register event. The event won't be raised until it's registered
> > and enabled. For those KVM owned events, they can't be registered
> > if they aren't exposed.
> >
> > Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
> > ---
> >   arch/arm64/kvm/sdei.c | 78 +++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 78 insertions(+)
> >
> > diff --git a/arch/arm64/kvm/sdei.c b/arch/arm64/kvm/sdei.c
> > index 3507e33ec00e..89c1b231cb60 100644
> > --- a/arch/arm64/kvm/sdei.c
> > +++ b/arch/arm64/kvm/sdei.c
> > @@ -25,6 +25,81 @@ static struct kvm_sdei_exposed_event exposed_events[] = {
> >   	for (idx = 0, event = &exposed_events[0];	\
> >   	     idx < ARRAY_SIZE(exposed_events);		\
> >   	     idx++, event++)
> > +#define kvm_sdei_for_each_event(vsdei, event, idx)	\
> > +	for (idx = 0, event = &vsdei->events[0];	\
> > +	     idx < ARRAY_SIZE(exposed_events);		\
> > +	     idx++, event++)
> > +
> > +static struct kvm_sdei_event *find_event(struct kvm_vcpu *vcpu,
> > +					 unsigned int num)
> > +{
> > +	struct kvm_sdei_vcpu *vsdei = vcpu->arch.sdei;
> > +	struct kvm_sdei_event *event;
> > +	int i;
> > +
> > +	kvm_sdei_for_each_event(vsdei, event, i) {
> > +		if (event->exposed_event->num == num)
> > +			return event;
> > +	}
> > +
> > +	return NULL;
> > +}
>
> I imagine you'll drop this hunk in the next spin.

Yes, I will :)

> > +static unsigned long hypercall_register(struct kvm_vcpu *vcpu)
>
> Hmm, hypercall_ is not a very descriptive scope. Could you instead do
> something like kvm_sdei_?
>
> so for this one, kvm_sdei_event_register()? Provides decent context
> clues to connect back to the spec as well.

Sure. I will revise the names of all functions for hypercalls and
remove "hypercall" prefix. For this particular case, I would use
event_register() because "kvm_sdei_" prefix has been reserved for
those global scoped functions :)

> > +{
> > +	struct kvm_sdei_vcpu *vsdei = vcpu->arch.sdei;
> > +	struct kvm_sdei_event *event;
> > +	unsigned int num = smccc_get_arg(vcpu, 1);
> > +	unsigned long ep_address = smccc_get_arg(vcpu, 2);
> > +	unsigned long ep_arg = smccc_get_arg(vcpu, 3);
>
> We discussed using some structure to track the registered context of an
> event. Maybe just build it on the stack then assign it in the array?

Yes, It will be something like below:

     struct kvm_sdei_event_handler handler = {
            .ep_address = smccc_get_arg(vcpu, 2),
            .ep_arg     = smccc_get_arg(vcpu, 3),
     };

> > +	unsigned long route_mode = smccc_get_arg(vcpu, 4);
>
> This is really 'flags'. route_mode is bit[0]. I imagine we don't want to
> support relative mode, so bit[1] is useless for us in that case too.
>
> The spec is somewhat imprecise on what happens for reserved flags. The
> prototype in section 5.1.2 of [1] suggests that reserved bits must be
> zero, but 5.1.2.3 'Client responsibilities' does not state that invalid
> flags result in an error.
>
> Arm TF certainly rejects unexpected flags [2].
>
> [1]: DEN0054C https://developer.arm.com/documentation/den0054/latest
> [2]: https://github.com/ARM-software/arm-trusted-firmware/blob/66c3906e4c32d675eb06bd081de8a3359f76b84c/services/std_svc/sdei/sdei_main.c#L260

Yes, This chunk of code is still stick to old specification. Lets
improve in next respin:

   - Rename @route_mode to @flags
   - Reject if the reserved bits are set.
   - Reject if relative mode (bit#1) is selected.
   - Reject if routing mode (bit#0) isn't RM_ANY (0).
   - @route_affinity will be dropped.

Thanks,
Gavin