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

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Message-Id: <50339bc0-50da-1a38-53a4-cf173fc387ea@linux.ibm.com>
Date:   Thu, 21 Feb 2019 13:40:33 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...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 19/02/2019 23:36, Tony Krowiak wrote:
> 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?

No I did not but in between I discovered an error in the handling of the 
interception of PQAP/AQIC.

QEMU and KVM can both accept PQAP/AQIC even if the vfio_ap driver is not 
loaded.
However now that the guest officially get the PQAP/AQIC instruction we 
need to handle the specification and operation exceptions inside KVM
_before_ testing and even calling the driver hook.

I will make the changes in the next iteration.

Regards,
Pierre



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