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

[Tony Krowiak]

On 04/16/2018 07:52 AM, Halil Pasic wrote:
> On 04/16/2018 01:13 PM, Pierre Morel wrote:
> > On 16/04/2018 12:51, 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@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > > >    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?
> > >
> > > 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
> > If I misunderstood and FEAT_AP really mean AP instructions available in the guest,
> > same question:
> > is this function called if AP instructions are not available in the guest?
> See patch #13. I guess the check above is anyway good as defensive
> programming. This implementation should be sane regardless of
> the answer to your question.

I agree.

> > > > +        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?
> > sorry, I should have written AP instructions here:
> > is this function called if AP instructions are not available in the guest?
> Yes, this function can be called with AP instructions available to the guest.
> Please have a look at patch 2 (kvm_s390_vm_set_crypto and the rest).
>
> Also this function is called on initialization regardless of AP instructions.
>
> > > > +        vcpu->arch.sie_block->eca |= ECA_APIE;
> > > > +
> > > > +
> > > >        if (!test_kvm_facility(vcpu->kvm, 76))
> > > >            return;