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SubjectRe: [PATCH v5 1/7] s390: ap: kvm: add PQAP interception for AQIC
On Wed, 13 Mar 2019 17:04:58 +0100
Pierre Morel <pmorel@linux.ibm.com> wrote:

> +/*
> + * handle_pqap: Handling pqap interception
> + * @vcpu: the vcpu having issue the pqap instruction
> + *
> + * We now support PQAP/AQIC instructions and we need to correctly
> + * answer the guest even if no dedicated driver's hook is available.
> + *
> + * The intercepting code calls a dedicated callback for this instruction
> + * if a driver did register one in the CRYPTO satellite of the
> + * SIE block.
> + *
> + * For PQAP/AQIC instructions only, verify privilege and specifications.
> + *
> + * If no callback available, the queues are not available, return this to
> + * the caller.
> + * Else return the value returned by the callback.
> + */
> +static int handle_pqap(struct kvm_vcpu *vcpu)
> +{
> + uint8_t fc;
> + struct ap_queue_status status = {};
> + int ret;
> + /* 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;
> + /* We do not want to change the behavior we had before this patch*/
> + if (fc != 0x03)
> + return -EOPNOTSUPP;
> +
> + /* PQAP instructions are allowed for guest kernel only */
> + if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
> + return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
> + /* AQIC instruction is allowed only if facility 65 is available */
> + if (!test_kvm_facility(vcpu->kvm, 65))
> + return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
> + /* Verify that the hook callback is registered and call it */
> + if (vcpu->kvm->arch.crypto.pqap_hook) {
> + if (!try_module_get(vcpu->kvm->arch.crypto.pqap_hook->owner))
> + return -EOPNOTSUPP;
> + ret = vcpu->kvm->arch.crypto.pqap_hook->hook(vcpu);
> + module_put(vcpu->kvm->arch.crypto.pqap_hook->owner);
> + return ret;
> + }
> + /*
> + * It is the duty of the vfio_driver to register a hook
> + * If it does not and we get an exception on AQIC we must
> + * guess that there is no vfio_ap_driver at all and no one
> + * to handle the guests's CRYCB and the CRYCB is empty.
> + */
> + status.response_code = 0x01;

I'm still confused here, sorry. From previous discussions I recall that
this indicates "no crypto device" (please correct me if I'm wrong.)

Before this patch, we had:
- guest issues PQAP/AQIC -> drop to userspace

With a correct implementation, we get:
- guest issues PQAP/AQIC -> callback does what needs to be done

With an incorrect implementation (no callback), we get:
- guest issues PQAP/AQIC -> guest gets response code 0x01

Why not drop to userspace in that case?


> + memcpy(&vcpu->run->s.regs.gprs[1], &status, sizeof(status));
> + return 0;
> +}
> +

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