Messages in this thread | | | Subject | Re: [PATCH v3 04/14] KVM: s390: device attribute to set AP interpretive execution | From | Tony Krowiak <> | Date | Thu, 15 Mar 2018 19:39:41 -0400 |
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On 03/15/2018 01:56 PM, Pierre Morel wrote: > On 15/03/2018 18:21, Tony Krowiak wrote: >> On 03/15/2018 11:45 AM, Pierre Morel wrote: >>> 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. >> It is not called from kvm_arch_vcpu_init(), it is called from >> kvm_arch_vcpu_setup(). > > hum, sorry for this. > However, the idea pertains, not to call this function from inside an > ioctl changing crypto parameters, but only during vcpu creation. Unfortunately, the ioctl does not get called until after the vcpus are created (see my comments below) > > > >> Also, >> this loop was already here, I did not put it in. Assuming whomever >> put it there did so >> for a reason, it is not my place to remove it. According to a trace I >> ran, the calls to this >> function occur after the vcpus are created. Consequently, the >> kvm_s390_vcpu_crypto_setup() >> function would not be called without the loop and neither the key >> wrapping support nor the >> ECA_APIE would be configured in the vcpu's SIE descriptor. >> >> If you have a better idea for where/how to set this flag, I'm all >> ears. It would be nice if it could be set before the vcpus are >> created, but I haven't >> found a good candidate. I suspect that the loop was put in to make >> sure that all vcpus >> get updated regardless of whether they are running or not, but I >> don't know what happens >> after a vcpu is kicked out of SIE. I suspect, as Halil surmised, that >> QEMU >> restores the vcpus to SIE. This would seemingly cause the >> kvm_arch_vcpu_setup() to get >> called at which time the ECA_APIE value as well as the key wrapping >> values will get set. >> If somebody has knowledge of the flow here, please feel free to pitch >> in. >>> >>> >>> >>>>> >>>>> >>>>> Pierre >>>>> >>>>> >>>>> >>>> >>> >> >
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