Re: [PATCH v4 1/7] s390: ap: kvm: add PQAP interception for AQIC

Tony Krowiak
2019-02-25T18:36:58Z

On 2/22/19 10:29 AM, Pierre Morel wrote:
> We prepare the interception of the PQAP/AQIC instruction for
> the case the AQIC facility is enabled in the guest.
>
> We add a callback inside the KVM arch structure for s390 for
> a VFIO driver to handle a specific response to the PQAP
> instruction with the AQIC command.
>
> We inject the correct exceptions from inside KVM for the case the
> callback is not initialized, which happens when the vfio_ap driver
> is not loaded.
>
> If the callback has been setup we call it.
> If not we setup an answer considering that no queue is available
> for the guest when no callback has been setup.
>
> We do consider the responsability of the driver to always initialize
> the PQAP callback if it defines queues by initializing the CRYCB for
> a guest.
>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
> arch/s390/include/asm/kvm_host.h | 1 +
> arch/s390/kvm/priv.c | 52 ++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 53 insertions(+)
>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index c5f5156..49cc8b0 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -719,6 +719,7 @@ struct kvm_s390_cpu_model {
>
> struct kvm_s390_crypto {
> struct kvm_s390_crypto_cb *crycb;
> + int (*pqap_hook)(struct kvm_vcpu *vcpu);
> __u32 crycbd;
> __u8 aes_kw;
> __u8 dea_kw;
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 8679bd7..3448abd 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -27,6 +27,7 @@
> #include <asm/io.h>
> #include <asm/ptrace.h>
> #include <asm/sclp.h>
> +#include <asm/ap.h>
> #include "gaccess.h"
> #include "kvm-s390.h"
> #include "trace.h"
> @@ -592,6 +593,55 @@ static int handle_io_inst(struct kvm_vcpu *vcpu)
> }
> }
>
> +/*
> + * 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 = {};
> +
> + /* Verify that the AP instruction are available */
> + if (!ap_instructions_available())
> + return -EOPNOTSUPP;

How can the guest even execute an AP instruction if the AP instructions
are not available? If the AP instructions are not available on the host,
they will not be available on the guest (i.e., CPU model feature
S390_FEAT_AP will not be set). I suppose it doesn't hurt to check this
here given QEMU may not be the only client.

> + /* 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;

You must have missed my suggestion to move this to the
vcpu->kvm->arch.crypto.pqap_hook(vcpu) in the following responses:

Message ID <342ffd56-b73a-b1f4-004d-de2c4aeef729@linux.ibm.com>
Message ID <e04f0c8b-2fd9-1846-334a-faa48e0e051e@linux.ibm.com>

You previously stated:

"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."

I don't know what any of the above has to do with checking FC=0x03? If
that check is moved to the pqap handler hook, it can just as well return
-EOPNOTSUPP. In fact, down below you do this:

return vcpu->kvm->arch.crypto.pqap_hook(vcpu);

If the RC=0x03 check fails in the hook, it will return -EOPNOTSUPP just
like above. None of this is critical, but the parsing of the register
values for the PQAP(AQIC) function ought to be done in the code that
handles the PQAP instruction IMHO.

> +
> + /* 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)
> + return vcpu->kvm->arch.crypto.pqap_hook(vcpu);
> +
> + /* PQAP/AQIC instructions are authorized but there is no queue */
> + status.response_code = 0x01;
> + memcpy(&vcpu->run->s.regs.gprs[1], &status, sizeof(status));
> + return 0;
> +}
> +
> static int handle_stfl(struct kvm_vcpu *vcpu)
> {
> int rc;
> @@ -878,6 +928,8 @@ int kvm_s390_handle_b2(struct kvm_vcpu *vcpu)
> return handle_sthyi(vcpu);
> case 0x7d:
> return handle_stsi(vcpu);
> + case 0xaf:
> + return handle_pqap(vcpu);
> case 0xb1:
> return handle_stfl(vcpu);
> case 0xb2:
>