Re: [PATCH v5 1/7] s390: ap: kvm: add PQAP interception for AQIC

Pierre Morel
2019-03-19T10:01:44Z

On 15/03/2019 18:28, Halil Pasic wrote:
> On Fri, 15 Mar 2019 14:26:34 +0100
> Pierre Morel <pmorel@linux.ibm.com> wrote:
>
>> On 15/03/2019 11:20, Cornelia Huck wrote:
>>> On Wed, 13 Mar 2019 17:04:58 +0100
>>> Pierre Morel <pmorel@linux.ibm.com> wrote:
>>>
>>>> +/*
>>>> + * handle_pqap: Handling pqap interception
>>>> + * @vcpu: the vcpu having issue the pqap instruction
>>>> + *
>>>> + * We now support PQAP/AQIC instructions and we need to correctly
>>>> + * answer the guest even if no dedicated driver's hook is available.
>>>> + *
>>>> + * The intercepting code calls a dedicated callback for this instruction
>>>> + * if a driver did register one in the CRYPTO satellite of the
>>>> + * SIE block.
>>>> + *
>>>> + * For PQAP/AQIC instructions only, verify privilege and specifications.
>>>> + *
>>>> + * If no callback available, the queues are not available, return this to
>>>> + * the caller.
>>>> + * Else return the value returned by the callback.
>>>> + */
>>>> +static int handle_pqap(struct kvm_vcpu *vcpu)
>>>> +{
>>>> + uint8_t fc;
>>>> + struct ap_queue_status status = {};
>>>> + int ret;
>>>> + /* Verify that the AP instruction are available */
>>>> + if (!ap_instructions_available())
>>>> + return -EOPNOTSUPP;
>>>> + /* Verify that the guest is allowed to use AP instructions */
>>>> + if (!(vcpu->arch.sie_block->eca & ECA_APIE))
>>>> + return -EOPNOTSUPP;
>>>> + /* Verify that the function code is AQIC */
>>>> + fc = vcpu->run->s.regs.gprs[0] >> 24;
>>>> + /* We do not want to change the behavior we had before this patch*/
>>>> + if (fc != 0x03)
>>>> + return -EOPNOTSUPP;
>>>> +
>>>> + /* PQAP instructions are allowed for guest kernel only */
>>>> + if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
>>>> + return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
>>>> + /* AQIC instruction is allowed only if facility 65 is available */
>>>> + if (!test_kvm_facility(vcpu->kvm, 65))
>>>> + return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
>>>> + /* Verify that the hook callback is registered and call it */
>>>> + if (vcpu->kvm->arch.crypto.pqap_hook) {
>>>> + if (!try_module_get(vcpu->kvm->arch.crypto.pqap_hook->owner))
>>>> + return -EOPNOTSUPP;
>>>> + ret = vcpu->kvm->arch.crypto.pqap_hook->hook(vcpu);
>>>> + module_put(vcpu->kvm->arch.crypto.pqap_hook->owner);
>>>> + return ret;
>>>> + }
>>>> + /*
>>>> + * It is the duty of the vfio_driver to register a hook
>>>> + * If it does not and we get an exception on AQIC we must
>>>> + * guess that there is no vfio_ap_driver at all and no one
>>>> + * to handle the guests's CRYCB and the CRYCB is empty.
>>>> + */
>>>> + status.response_code = 0x01;
>>>
>>> I'm still confused here, sorry. From previous discussions I recall that
>>> this indicates "no crypto device" (please correct me if I'm wrong.)
>>>
>>> Before this patch, we had:
>>> - guest issues PQAP/AQIC -> drop to userspace
>>>
>>> With a correct implementation, we get:
>>> - guest issues PQAP/AQIC -> callback does what needs to be done
>>>
>>> With an incorrect implementation (no callback), we get:
>>> - guest issues PQAP/AQIC -> guest gets response code 0x01
>>>
>>> Why not drop to userspace in that case?
>>
>> This is what I had in the previous patches.
>> Hum, I do not remember which discussion lead me to modify this.
>>
>> Anyway, now that you put the finger on this problem, I think the problem
>> is worse.
>>
>> The behavior with old / new Linux, vfio driver and qemu is:
>>
>> LINUX VFIO_AP QEMU PGM
>> OLD x x OPERATION
>
> Isn't OPERATION a bad answer if ap=on? It should not happen
> with a well behaved guest because facility 65 is not indicated,
> but if it does, I guess we give the wrong answer.

It is clearly wrong but we can not change the past :)

>
>> NEW - OLD SPECIFICATION
>> NEW - NEW/aqic=off SPECIFICATION
>> NEW x NEW/aqic=on -
>>
>
> AFAICT with LINUX == NEW we get the correct answer. OPERATION exception
> is only good if ap=off.

Exact.

>
>> x = whatever
>> - = absent/none
>>
>> So yes there is a change in behavior for the userland for the case QEMU
>> do not set the AQIC facility 65, OLD QEMU or NEW QEMU wanting to behave
>> like an older one.
>>
>> I fear we have the same problem with the privileged operation...
>>
>
> IMHO this boils down to:
> * either OLD QEMU or
> * OLD LINUX
> should have taken care of handling the mandatory intercept for PQAP/AQIC
> if ap=on (i.e. guest has AP instructions), and does not have facility 65
> which was the case for OLD.

yes

>
> Things get complicated when one considers that ECA.28 is an effective
> control.

I don't think so, ECA_28 is not really a problem.
We do not propagate ECA_AIV in VSIE and ECA_AIV is tested in the vfio
driver to support GISA.
So that the guest 3 will not support interrupt.

>
>> For the last case, when the kvm_facility(65) is set, the explication is
>> the following:
>>
>> This is related to the handling of PQAP AQIC which is now authorized by
>> this patch series.
>> If we authorize PQAP AQIC, by setting the bit for facility 65, the guest
>> can use this instruction.
>> If the instruction follows the specifications we must answer something
>> realistic and since there is nothing in the CRYCB (no driver) we answer
>> that there is no queue.
>>
>> Conclusion: we must handle this in userland, it will have the benefit
>> to keep old behavior when there is no callback.
>> OLD QEMU will not see change as they will not set aqic facility
>
> That would mean we remain quirky.

Yes, the alternative is:

1) We do things right but this mean we change the ABI (SPECIFICATION
instead of OPERATION)

I thing this is the best thing to do, it is the implementation proposed
by this patch where all is done in Kernel, so that we are right what
ever the userland user is (QEMU or other).

2) We want to preserve the old ABI for old QEMU
Then I proposed the implementation here under.

My personal opinion, is that we should change the ABI and do things
right now.
We should also do it right for TAPQ with t bit set. I remember Christian
already warned about this but we did not implement it.

>
>> NEW QEMU will handle this correctly.
>>
>> In this case we also do not need to handle all other tests here but can
>> move it to the callback as Tony wanted.
>>
>> Would you agree with something simple like:
>>
>> static int handle_pqap(struct kvm_vcpu *vcpu)
>> {
>> int ret = -EOPNOTSUPP;
>>
>> /* Verify that the hook callback is registered and call it */
>> if (pqap_hook)
>> if (try_module_get(pqap_hook->owner)) {
>> ret = pqap_hook->hook(vcpu);
>> module_put(pqap_hook->owner);
>> }
>> return ret;
>> }
>>
>> All other tests in QEMU and in the callback.
>>
>
> You stated in another email that the conclusion is wrong. I'm not sure

Forget it, I do not understand what I wanted to say there /o\ .

> what is the cleanest solution here. This effective control thing does
> make my head spin.

As I said I do not thing any effective control do interfere here.
IMHO Alternative 1 is the cleanest solution

Regards,
Pierre

--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany