Re: [PATCH v4 05/15] KVM: s390: enable/disable AP interpretive execution

Pierre Morel
2018-04-18T08:31:08Z

On 17/04/2018 20:11, Tony Krowiak wrote:
> On 04/17/2018 12:55 PM, Pierre Morel wrote:
>> On 17/04/2018 18:22, Tony Krowiak wrote:
>>> On 04/17/2018 12:13 PM, Pierre Morel wrote:
>>>> On 17/04/2018 17:02, Tony Krowiak wrote:
>>>>> On 04/16/2018 06:51 AM, Pierre Morel wrote:
>>>>>> On 15/04/2018 23:22, Tony Krowiak wrote:
>>>>>>> The VFIO AP device model exploits interpretive execution of AP
>>>>>>> instructions (APIE) to provide guests passthrough access to AP
>>>>>>> devices. This patch introduces a new interface to enable and
>>>>>>> disable APIE.
>>>>>>>
>>>>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.vnet.ibm.com>
>>>>>>> ---
>>>>>>>   arch/s390/include/asm/kvm-ap.h   |   16 ++++++++++++++++
>>>>>>>   arch/s390/include/asm/kvm_host.h |    1 +
>>>>>>>   arch/s390/kvm/kvm-ap.c           |   20 ++++++++++++++++++++
>>>>>>>   arch/s390/kvm/kvm-s390.c         |    9 +++++++++
>>>>>>>   4 files changed, 46 insertions(+), 0 deletions(-)
>>>>>>>
>>>>>>> diff --git a/arch/s390/include/asm/kvm-ap.h
>>>>>>> b/arch/s390/include/asm/kvm-ap.h
>>>>>>> index 736e93e..a6c092e 100644
>>>>>>> --- a/arch/s390/include/asm/kvm-ap.h
>>>>>>> +++ b/arch/s390/include/asm/kvm-ap.h
>>>>>>> @@ -35,4 +35,20 @@
>>>>>>>    */
>>>>>>>   void kvm_ap_build_crycbd(struct kvm *kvm);
>>>>>>>
>>>>>>> +/**
>>>>>>> + * kvm_ap_interpret_instructions
>>>>>>> + *
>>>>>>> + * Indicate whether AP instructions shall be interpreted. If
>>>>>>> they are not
>>>>>>> + * interpreted, all AP instructions will be intercepted and
>>>>>>> routed back to
>>>>>>> + * userspace.
>>>>>>> + *
>>>>>>> + * @kvm: the virtual machine attributes
>>>>>>> + * @enable: indicates whether AP instructions are to be
>>>>>>> interpreted (true) or
>>>>>>> + *        or not (false).
>>>>>>> + *
>>>>>>> + * Returns 0 if completed successfully; otherwise, returns
>>>>>>> -EOPNOTSUPP
>>>>>>> + * indicating that AP instructions are not installed on the guest.
>>>>>>> + */
>>>>>>> +int kvm_ap_interpret_instructions(struct kvm *kvm, bool enable);
>>>>>>> +
>>>>>>>   #endif /* _ASM_KVM_AP */
>>>>>>> diff --git a/arch/s390/include/asm/kvm_host.h
>>>>>>> b/arch/s390/include/asm/kvm_host.h
>>>>>>> index 3162783..5470685 100644
>>>>>>> --- a/arch/s390/include/asm/kvm_host.h
>>>>>>> +++ b/arch/s390/include/asm/kvm_host.h
>>>>>>> @@ -715,6 +715,7 @@ struct kvm_s390_crypto {
>>>>>>>       __u32 crycbd;
>>>>>>>       __u8 aes_kw;
>>>>>>>       __u8 dea_kw;
>>>>>>> +    __u8 apie;
>>>>>>>   };
>>>>>>>
>>>>>>>   #define APCB0_MASK_SIZE 1
>>>>>>> diff --git a/arch/s390/kvm/kvm-ap.c b/arch/s390/kvm/kvm-ap.c
>>>>>>> index 991bae4..55d11b5 100644
>>>>>>> --- a/arch/s390/kvm/kvm-ap.c
>>>>>>> +++ b/arch/s390/kvm/kvm-ap.c
>>>>>>> @@ -58,3 +58,23 @@ void kvm_ap_build_crycbd(struct kvm *kvm)
>>>>>>>       }
>>>>>>>   }
>>>>>>>   EXPORT_SYMBOL(kvm_ap_build_crycbd);
>>>>>>> +
>>>>>>> +int kvm_ap_interpret_instructions(struct kvm *kvm, bool enable)
>>>>>>> +{
>>>>>>> +    int ret = 0;
>>>>>>> +
>>>>>>> +    mutex_lock(&kvm->lock);
>>>>>>> +
>>>>>>> +    if (!test_kvm_cpu_feat(kvm, KVM_S390_VM_CPU_FEAT_AP)) {
>>>>>>
>>>>>> Do we really need to test CPU_FEAT_AP?
>>>>>
>>>>> Yes we do.
>>>>
>>>> really? why?
>>>
>>> The KVM_S390_VM_CPU_FEAT_AP will not be enabled by KVM if the AP
>>> instructions are not installed on the host. I assume - but have
>>> no way of verifying - that if the AP instructions are not installed
>>> on the host, that interpretation would fail. Do you know what would
>>> happen if AP instructions are interpreted when not installed on
>>> the host?
>>
>> If the host has no AP instructions (his ECA.28=0) but it set ECA.28
>> for a guest,
>> there will be no AP instructions available in the guest.
>
> Then there's the answer to your question; this is why we to test
> CPU_FEAT_AP.

We can postpone this discussion when we discuss on VSIE.
For this specific call I just wanted to point out that obviously this
function should not
be called if the guest has no AP instructions.

>
>>
>>
>>>
>>>>
>>>>
>>>>>
>>>>>>
>>>>>>
>>>>>> I understand that KVM_S390_VM_CPU_FEAT_AP means AP instructions
>>>>>> are interpreted.
>>>>>> shouldn't we add this information in the name?
>>>>>> like KVM_S390_VM_CPU_FEAT_APIE
>>>>>
>>>>> KVM_S390_VM_CPU_FEAT_AP does NOT mean AP instructions are
>>>>> interpreted, it means
>>>>> AP instructions are installed.
>>>>
>>>> Right same error I made all along this review.
>>>> But AFAIK it means AP instructions are provided to the guest.
>>>> Then should this function be called if the guest has no AP
>>>> instructions ?
>>>>
>>>>
>>>>>
>>>>>>
>>>>>>> +        ret = -EOPNOTSUPP;
>>>>>>> +        goto done;
>>>>>>> +    }
>>>>>>> +
>>>>>>> +    kvm->arch.crypto.apie = enable;
>>>>>>> +    kvm_s390_vcpu_crypto_reset_all(kvm);
>>>>>>> +
>>>>>>> +done:
>>>>>>> +    mutex_unlock(&kvm->lock);
>>>>>>> +    return ret;
>>>>>>> +}
>>>>>>> +EXPORT_SYMBOL(kvm_ap_interpret_instructions);
>>>>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>>>>> index 55cd897..1dc8566 100644
>>>>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>>>>> @@ -1901,6 +1901,9 @@ static void kvm_s390_crypto_init(struct
>>>>>>> kvm *kvm)
>>>>>>>       kvm->arch.crypto.crycb = &kvm->arch.sie_page2->crycb;
>>>>>>>       kvm_ap_build_crycbd(kvm);
>>>>>>>
>>>>>>> +    /* Default setting indicating SIE shall interpret AP
>>>>>>> instructions */
>>>>>>> +    kvm->arch.crypto.apie = 1;
>>>>>>> +
>>>>>>>       if (!test_kvm_facility(kvm, 76))
>>>>>>>           return;
>>>>>>>
>>>>>>> @@ -2434,6 +2437,12 @@ static void
>>>>>>> kvm_s390_vcpu_crypto_setup(struct kvm_vcpu *vcpu)
>>>>>>>   {
>>>>>>>       vcpu->arch.sie_block->crycbd = vcpu->kvm->arch.crypto.crycbd;
>>>>>>>
>>>>>>> +    vcpu->arch.sie_block->eca &= ~ECA_APIE;
>>>>>>> +    if (vcpu->kvm->arch.crypto.apie &&
>>>>>>> +        test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_AP))
>>>>>>
>>>>>> Do we call xxx_crypto_setup() if KVM does not support AP
>>>>>> interpretation?
>>>>>
>>>>> Yes, kvm_s390_vcpu_crypto_setup(vcpu) is called by
>>>>> kvm_arch_vcpu_setup(vcpu)
>>>>> as well as from kvm_s390_vcpu_crypto_reset_all(kvm). Calling it
>>>>> has nothing
>>>>> to do with whether AP interpretation is supported or not as it
>>>>> does much
>>>>> more than that, including setting up of wrapping keys and the CRYCBD.
>>>>
>>>> Sorry, still the same error I made about CPU_FEAT_AP meaning AP
>>>> instructions in the guest
>>>> and not AP interpretation available.
>>>> Could apie be set if AP instruction are not supported?
>>>>
>>>>>
>>>>>>
>>>>>>> + vcpu->arch.sie_block->eca |= ECA_APIE;
>>>>>>> +
>>>>>>> +
>>>>>>>       if (!test_kvm_facility(vcpu->kvm, 76))
>>>>>>>           return;
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>

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