linux-kernel - Re: [PATCH v3 04/14] KVM: s390: device attribute to set AP interpretive execution

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Message-Id: <b781deb9-5fdc-1809-8e3c-3858e10aa944@linux.vnet.ibm.com>
Date:   Mon, 2 Apr 2018 14:55:46 -0400
From:   Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
To:     Halil Pasic <pasic@...ux.vnet.ibm.com>,
        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, berrange@...hat.com, fiuczy@...ux.vnet.ibm.com,
        buendgen@...ibm.com
Subject: Re: [PATCH v3 04/14] KVM: s390: device attribute to set AP
 interpretive execution

On 03/20/2018 06:48 PM, Halil Pasic wrote:
>
> On 03/20/2018 06:58 PM, Tony Krowiak wrote:
>> I spoke with Christian this morning and he made a suggestion which I think would provide the best solution here.
>> This is my proposal:
>> 1. Get rid of the KVM_S390_VM_CRYPTO_INTERPRET_AP device attribute and return to setting ECA.28 from the
>>     mdev device open callback.
>> 2. Since there may be vcpus online at the time the mdev device open is called, we must first take all running vcpus out of
>>     SIE and block them. Christian suggested the kvm_s390_vcpu_block_all(struct kvm *kvm) function will do the trick. So I
>>     propose introducing a function like the following to be called during mdev open:
> There is one thing you missed, otherwise I'm *very* satisfied with this
> proposal.
>
> What you have missed IMHO is vcpu hottplug. So IMHO you should keep
> kvm->arch.crypto.apie, and update it accordingly ...
I agree, I will fix it.
>
>
>>      int kvm_ap_set_interpretive_exec(struct kvm *kvm, bool enable)
>>      {
>>          int i;
>>          struct kvm_vcpu *vcpu;
>>
>>          if (!test_kvm_cpu_feat(kvm, KVM_S390_VM_CPU_FEAT_AP))
>>              return -EOPNOTSUPP;
>>
>>          mutex_lock(&kvm->lock);
>>
>>          kvm_s390_vcpu_block_all(kvm);
> ... let's say here.
Yep
>
>>          kvm_for_each_vcpu(i, vcpu, kvm) {
> And here you can call kvm_s390_vcpu_crypto_setup(vcpu) (the changes to
> this function will be required for hotplug) if you like
Sounds good to me.
>
>>              if (enable)
>>                  vcpu->arch.sie_block->eca |= ECA_APIE;
>>              else
>>                  vcpu->arch.sie_block->eca &= ~ECA_APIE;
> or keep this stuff, it does not really matter to me.
I'll call the kvm_s390_vcpu_crypto_setup(vcpu) to set ECA_APIE.
>
>>          }
>>
>>          kvm_s390_vcpu_unblock_all(kvm);
>>
>>          mutex_unlock(&kvm->lock);
>>
>>          return 0;
>>      }
>>
>>     This interface allows us to set ECA.28 even if vcpus are running
> I tend to agree. I will give it a proper review when this gets more
> formal (e.g. v4 (preferably) or patches to be fixed up to this series).
>
> Please don't forget to revisit the discussion on kvm_s390_vm_set_crypto:
> if the mechanism there isn't right for ECA.28 I think you should tell
> us why it's OK for the other attributes if it's OK. If it is not then
> I guess you will want to do a stand alone patch for that.
That will no longer be a part of this patch series. We can revisit that as
a separate issue at a future time.
>