linux-kernel - Re: [PATCH v6 04/18] KVM: arm64: Support SDEI_EVENT

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Date:   Mon, 2 May 2022 10:55:51 +0800
From:   Gavin Shan <gshan@...hat.com>
To:     Oliver Upton <oupton@...gle.com>
Cc:     kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        eauger@...hat.com, Jonathan.Cameron@...wei.com,
        vkuznets@...hat.com, will@...nel.org, shannon.zhaosl@...il.com,
        james.morse@....com, mark.rutland@....com, maz@...nel.org,
        pbonzini@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH v6 04/18] KVM: arm64: Support SDEI_EVENT_REGISTER
 hypercall

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@...hat.com>
>> ---
>>   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