linux-kernel - Re: [PATCH v3 2/9] s390: ap: kvm: setting a hook for PQAP instructions

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Message-Id: <e04f0c8b-2fd9-1846-334a-faa48e0e051e@linux.ibm.com>
Date:   Tue, 19 Feb 2019 17:36:38 -0500
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     pmorel@...ux.ibm.com, Cornelia Huck <cohuck@...hat.com>
Cc:     borntraeger@...ibm.com, alex.williamson@...hat.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, frankja@...ux.ibm.com, pasic@...ux.ibm.com,
        david@...hat.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, freude@...ux.ibm.com, mimu@...ux.ibm.com
Subject: Re: [PATCH v3 2/9] s390: ap: kvm: setting a hook for PQAP
 instructions

On 2/19/19 2:50 PM, Pierre Morel wrote:
> On 18/02/2019 23:42, Cornelia Huck wrote:
>> On Mon, 18 Feb 2019 19:29:10 +0100
>> Pierre Morel <pmorel@...ux.ibm.com> wrote:
>>
>>> On 15/02/2019 23:02, Tony Krowiak wrote:
>>>> On 2/14/19 8:51 AM, Pierre Morel wrote:
>>
>>>>> +/*
>>>>> + * handle_pqap: Handling pqap interception
>>>>> + * @vcpu: the vcpu having issue the pqap instruction
>>>>> + *
>>>>> + * This callback only handles PQAP/AQIC instruction and
>>>>> + * calls a dedicated callback for this instruction if
>>>>> + * a driver did register one in the CRYPTO satellite of the
>>>>> + * SIE block.
>>>>> + *
>>>>> + * Do not change the behavior if, return -EOPNOTSUPP if:
>>>>> + * - the hook is not used do not change the behavior.
>>>>> + * - AP instructions are not available or not available to the guest
>>>>> + * - the instruction is not PQAP with function code indicating
>>>>> + *   AQIC do not change the previous behavior.
>>>>> + *
>>>>> + * For PQAP/AQIC instruction, verify privilege and specifications
>>>>> + *
>>>>> + * return the value returned by the callback.
>>>>> + */
>>>>> +static int handle_pqap(struct kvm_vcpu *vcpu)
>>>>> +{
>>>>> +    uint8_t fc;
>>>>> +
>>>>> +    /* Verify that the hook callback is registered */
>>>>> +    if (!vcpu->kvm->arch.crypto.pqap_hook)
>>>>> +        return -EOPNOTSUPP;
>>>>> +    /* 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;
>>>>> +    if (fc != 0x03)
>>>>> +        return -EOPNOTSUPP;
>>>>
>>>> This does not belong here. Function code 3 is one of 7 function codes
>>>> that can be sent with the PQAP instruction. This belongs in the PQAP
>>>> hook code.
>>>
>>> On one hand, effectively I would prefer to put the code in the VFIO
>>> driver code.
>>> On the other hand, doing this would lead to export the code for
>>> test_kvm_facility() and kvm_s390_inject_program_int() from the 
>>> kvm-s390.h
>>>
>>> I choose not to export these functions from the KVM code.
>>>
>>> Would like opinion from KVM maintainers?
>>
>> Looking at this (and without access to the specification...), I think
>> the check for problem state makes sense in here (if this applies to all
>> PQAP functions equally, which seems likely). The check for the facility
>> makes more sense in the handler. You can probably still inject the
>> specification exception here if you use a clever return code.
>>
> 
> If there is no objection on exporting the KVM functions... I can do this.

I do not understand why you would have to export KVM functions to place
the check for FC 0x03 in the pqap hook? What am I missing here? Maybe
you misunderstood my comment? The following is the only code I suggested
you move:

+    fc = vcpu->run->s.regs.gprs[0] >> 24;
+    if (fc != 0x03)
+        return -EOPNOTSUPP;

What does that have to do with test_kvm_facility() and
kvm_s390_inject_program_int()? Please explain.

> 
>> Another option: Provide a way to register a callback per function code;
>> this allows you to still do the check here and extend it later for
>> other function codes (which will probably be indicated by another
>> facility).
> 
> I like this option even better.
> 
> Regards,
> Pierre
> 
>