Messages in this thread | | | Subject | Re: [PATCH v3 04/14] KVM: s390: device attribute to set AP interpretive execution | From | Pierre Morel <> | Date | Thu, 15 Mar 2018 16:45:35 +0100 |
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On 15/03/2018 16:26, Tony Krowiak wrote: > On 03/15/2018 09:00 AM, Pierre Morel wrote: >> On 14/03/2018 22:57, Halil Pasic wrote: >>> >>> On 03/14/2018 07:25 PM, 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 device attribute in the >>>> KVM_S390_VM_CRYPTO device attribute group to set APIE from >>>> the VFIO AP device defined on the guest. >>>> >>>> Signed-off-by: Tony Krowiak <akrowiak@linux.vnet.ibm.com> >>>> --- >>> [..] >>> >>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>>> index a60c45b..bc46b67 100644 >>>> --- a/arch/s390/kvm/kvm-s390.c >>>> +++ b/arch/s390/kvm/kvm-s390.c >>>> @@ -815,6 +815,19 @@ static int kvm_s390_vm_set_crypto(struct kvm >>>> *kvm, struct kvm_device_attr *attr) >>>> sizeof(kvm->arch.crypto.crycb->dea_wrapping_key_mask)); >>>> VM_EVENT(kvm, 3, "%s", "DISABLE: DEA keywrapping support"); >>>> break; >>>> + case KVM_S390_VM_CRYPTO_INTERPRET_AP: >>>> + if (attr->addr) { >>>> + if (!test_kvm_cpu_feat(kvm, KVM_S390_VM_CPU_FEAT_AP)) >>> Unlock mutex before returning? >>> >>> Maybe flip conditions (don't allow manipulating apie if feature not >>> there). >>> Clearing the anyways clear apie if feature not there ain't too bad, but >>> rejecting the operation appears nicer to me. >>> >>>> + return -EOPNOTSUPP; >>>> + kvm->arch.crypto.apie = 1; >>>> + VM_EVENT(kvm, 3, "%s", >>>> + "ENABLE: AP interpretive execution"); >>>> + } else { >>>> + kvm->arch.crypto.apie = 0; >>>> + VM_EVENT(kvm, 3, "%s", >>>> + "DISABLE: AP interpretive execution"); >>>> + } >>>> + break; >>>> default: >>>> mutex_unlock(&kvm->lock); >>>> return -ENXIO; >>> I wonder how the loop after this switch works for >>> KVM_S390_VM_CRYPTO_INTERPRET_AP: >>> >>> kvm_for_each_vcpu(i, vcpu, kvm) { >>> kvm_s390_vcpu_crypto_setup(vcpu); >>> exit_sie(vcpu); >>> } >>> >>> From not doing something like for KVM_S390_VM_CRYPTO_INTERPRET_AP >>> >>> if (kvm->created_vcpus) { >>> mutex_unlock(&kvm->lock); >>> return -EBUSY; >>> and from the aforementioned loop I guess ECA.28 can be changed >>> for a running guest. >>> >>> If there are running vcpus when KVM_S390_VM_CRYPTO_INTERPRET_AP is >>> changed (set) these will be taken out of SIE by exit_sie(). Then for >>> the >>> corresponding threads the control probably goes to QEMU (the >>> emulator in >>> the userspace). And it puts that vcpu back into the SIE, and then that >>> cpu starts acting according to the new ECA.28 value. While other vcpus >>> may still work with the old value of ECA.28. >>> >>> I'm not saying what I describe above is necessarily something broken. >>> But I would like to have it explained, why is it OK -- provided I >>> did not >>> make any errors in my reasoning (assumptions included). >>> >>> Can you help me understand this code? >>> >>> Regards, >>> Halil >>> >>> [..] >>> >> >> I have the same concerns as Halil. >> >> We do not need to change the virtulization type >> (hardware/software) on the fly for the current use case. >> >> Couldn't we delay this until we have one and in between only make the >> vCPU hotplug clean? >> >> We only need to let the door open for the day we have such a use case. > Are you suggesting this code be removed? If so, then where and under > what conditions would > you suggest setting ECA.28 given you objected to setting it based on > whether the > AP feature is installed?
I would only call kvm_s390_vcpu_crypto_setup() from inside kvm_arch_vcpu_init() as it is already.
>> >> >> Pierre >> >> >> >
-- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany
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