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

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Date:   Tue, 17 Apr 2018 14:11:11 -0400
From:   Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
To:     Pierre Morel <pmorel@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, buendgen@...ibm.com
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
        alex.williamson@...hat.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com
Subject: Re: [PATCH v4 05/15] KVM: s390: enable/disable AP interpretive
 execution

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@...ux.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.

>
>
>>
>>>
>>>
>>>>
>>>>>
>>>>>
>>>>> 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;
>>>>>>
>>>>>
>>>>
>>>
>>
>