Messages in this thread | | | Subject | Re: [PATCH v4 05/15] KVM: s390: enable/disable AP interpretive execution | From | Tony Krowiak <> | Date | Tue, 17 Apr 2018 12:34:16 -0400 |
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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?
Answered this in Message ID: <2b053349-071e-17ed-6ebd-a37bcfd2f330@linux.vnet.ibm.com>
> >> >>> >>> >>> 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 ?
Same answer as below. We have no control over who calls this interface, so it behooves us to make sure it isn't called erroneously. I despise reading code where I have to search all of the callers to ensure they perform a required check ... why not just do it in the interface.
> > > >> >>> >>>> + 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?
Only if code authors and reviewers ensure that no future code changes set the apie flag when the CPU_FEAT_AP is not set. Why do you see this as a problem? I see it as defensive coding since we have no control over who calls this interface.
> > >> >>> >>>> + vcpu->arch.sie_block->eca |= ECA_APIE; >>>> + >>>> + >>>> if (!test_kvm_facility(vcpu->kvm, 76)) >>>> return; >>>> >>> >> >
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