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

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Message-Id: <74d812c6-bf83-0fb0-8fc3-af1341b0ae3c@linux.ibm.com>
Date:   Tue, 19 Feb 2019 20:50:58 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     Tony Krowiak <akrowiak@...ux.ibm.com>, 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 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.

> 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


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