Re: [PATCH v4 02/15] KVM: s390: reset crypto attributes for all vcpus

[Tony Krowiak]

On 04/17/2018 07:34 AM, Cornelia Huck wrote:
> On Sun, 15 Apr 2018 17:22:12 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx> wrote:
>
> > Introduces a new function to reset the crypto attributes for all
> > vcpus whether they are running or not. Each vcpu in KVM will
> > be removed from SIE prior to resetting the crypto attributes in its
> > SIE state description. After all vcpus have had their crypto attributes
> > reset the vcpus will be restored to SIE.
> >
> > This function will be used in a later patch to set the ECA.28
> > bit in the SIE state description to enable interpretive execution of
> > AP instructions. It will also be incorporated into the
> > kvm_s390_vm_set_crypto(kvm) function to fix an issue whereby the crypto
> > key wrapping attributes could potentially get out of synch for running
> > vcpus.
> So, this description leads me to think it would make sense to queue
> this patch (fixing the key wrapping) independently of this series,
> wouldn't it?
I considered that because I figured there might be objections, but
since separating them would create dependency issues I didn't see
any harm in including it here. I can remove this from the explanation
above and the code below and create a separate patch for the key
wrapping if you'd prefer.
> > Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx>
> > ---
> >   arch/s390/kvm/kvm-s390.c |   19 +++++++++++++------
> >   arch/s390/kvm/kvm-s390.h |   14 ++++++++++++++
> >   2 files changed, 27 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index 64c9862..d0c3518 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -791,11 +791,21 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
> >   
> >   static void kvm_s390_vcpu_crypto_setup(struct kvm_vcpu *vcpu);
> >   
> > -static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
> > +void kvm_s390_vcpu_crypto_reset_all(struct kvm *kvm)
> _reset_all() or _set_all()? Don't really care much, tbh.
Then why bring it up?:) I chose _reset_all because in both places from which
this is called, we are changing a crypto attribute value and are thus
resetting the crypto settings for all the vcpus.
> >   {
> > -	struct kvm_vcpu *vcpu;
> >   	int i;
> > +	struct kvm_vcpu *vcpu;
> I'd avoid swapping the order of the declarations.
This was unintentional, I can revert it.
> > +
> > +	kvm_s390_vcpu_block_all(kvm);
> > +
> > +	kvm_for_each_vcpu(i, vcpu, kvm)
> > +		kvm_s390_vcpu_crypto_setup(vcpu);
> >   and
> > +	kvm_s390_vcpu_unblock_all(kvm);
> > +}
> > +
> > +static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
> > +{
> >   	if (!test_kvm_facility(kvm, 76))
> >   		return -EINVAL;
> >   
> > @@ -832,10 +842,7 @@ static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
> >   		return -ENXIO;
> >   	}
> >   
> > -	kvm_for_each_vcpu(i, vcpu, kvm) {
> > -		kvm_s390_vcpu_crypto_setup(vcpu);
> > -		exit_sie(vcpu);
> > -	}
> > +	kvm_s390_vcpu_crypto_reset_all(kvm);
> >   	mutex_unlock(&kvm->lock);
> >   	return 0;
> >   }
> > diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
> > index 1b5621f..76324b7 100644
> > --- a/arch/s390/kvm/kvm-s390.h
> > +++ b/arch/s390/kvm/kvm-s390.h
> > @@ -410,4 +410,18 @@ static inline int kvm_s390_use_sca_entries(void)
> >   }
> >   void kvm_s390_reinject_machine_check(struct kvm_vcpu *vcpu,
> >   				     struct mcck_volatile_info *mcck_info);
> > +
> > +/**
> > + * kvm_s390_vcpu_crypto_reset_all
> > + *
> > + * Reset the crypto attributes for each vcpu. This can be done while the vcpus
> > + * are running as each vcpu will be removed from SIE before resetting the crypto
> > + * attributes and restored to SIE afterward.
> > + *
> > + * Note: The kvm->lock mutex must be locked prior to calling this function and
> > + *	 unlocked after it returns.
> "Must be called with kvm->lock held"?
Yes. The kvm->lock must be held to set the crypto attributes that will be
copied to the vcpus via the kvm_s390_vcpu_crypto_reset_all() function,
so it made sense to hold the lock across the entire operation.

> > + *
> > + * @kvm: the KVM guest
> > + */
> > +void kvm_s390_vcpu_crypto_reset_all(struct kvm *kvm);
> >   #endif
> Other than the nits above, looks good to me.
Great!
>