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

[Pierre Morel]

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.

> 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 BÃblingen - Germany