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

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Message-Id: <cf928702-db64-93c7-9b89-bf1c66a33cfa@linux.vnet.ibm.com>
Date:   Tue, 17 Apr 2018 11:02:06 -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
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, buendgen@...ibm.com
Subject: Re: [PATCH v4 05/15] KVM: s390: enable/disable AP interpretive
 execution

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.

>
>
> 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.

>
>> +        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.

>
>> +        vcpu->arch.sie_block->eca |= ECA_APIE;
>> +
>> +
>>       if (!test_kvm_facility(vcpu->kvm, 76))
>>           return;
>>
>