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

Pierre Morel
2018-04-17T16:55:08Z

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.

>
>>
>>
>>>
>>>>
>>>>
>>>> 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