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

[Tony Krowiak]

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@xxxxxxxxxxxxx> 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
> > > > > + *ÂÂ 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)
> > > > > +{
> > > > > +ÂÂÂ uint8_t fc;
> > > > > +
> > > > > +ÂÂÂ /* Verify that the hook callback is registered */
> > > > > +ÂÂÂ if (!vcpu->kvm->arch.crypto.pqap_hook)
> > > > > +ÂÂÂÂÂÂÂ return -EOPNOTSUPP;
> > > > > +ÂÂÂ /* Verify that the AP instruction are available */
> > > > > +ÂÂÂ if (!ap_instructions_available())
> > > > > +ÂÂÂÂÂÂÂ return -EOPNOTSUPP;
> > > > > +ÂÂÂ /* Verify that the guest is allowed to use AP instructions */
> > > > > +ÂÂÂ if (!(vcpu->arch.sie_block->eca & ECA_APIE))
> > > > > +ÂÂÂÂÂÂÂ return -EOPNOTSUPP;
> > > > > +ÂÂÂ /* Verify that the function code is AQIC */
> > > > > +ÂÂÂ fc = vcpu->run->s.regs.gprs[0] >> 24;
> > > > > +ÂÂÂ if (fc != 0x03)
> > > > > +ÂÂÂÂÂÂÂ 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 think I understand where you are coming from. In looking back at the
original patch, I see there are checks using the test_kvm_facility and
kvm_s390_inject_program_int functions placed after your check for
fc != 0x03. You clearly misunderstood what I was asking you to do.
I was suggesting that ONLY the check for 'fc != 0x03' be done in the
hook. I was NOT suggesting the instructions following the check for
fc != 0x03 be done in the hook, so there is no need to export any KVM
functions.


> > 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