linux-kernel - Re: [PATCH] KVM: s390: reset crypto attributes for all vcpus

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Date:   Sun, 22 Apr 2018 11:06:43 -0400
From:   Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
To:     David Hildenbrand <david@...hat.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     borntraeger@...ibm.com, cohuck@...hat.com,
        pmorel@...ux.vnet.ibm.com, pasic@...ux.vnet.ibm.com,
        pbonzini@...hat.com, rkrcmar@...hat.com
Subject: Re: [PATCH] KVM: s390: reset crypto attributes for all vcpus

On 04/20/2018 08:26 AM, David Hildenbrand wrote:
> On 19.04.2018 23:13, Tony Krowiak 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 is incorporated into the kvm_s390_vm_set_crypto(kvm)
>> function to fix a reported issue whereby the crypto key wrapping
>> attributes could potentially get out of synch for running vcpus.
>>
>> Reported-by: Halil Pasic <pasic@...ux.vnet.ibm.com>
> A reported-by for a code refactoring is strange.

I was asked to include this.

>
>> Signed-off-by: Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
>> ---
>>   arch/s390/kvm/kvm-s390.c |   18 ++++++++++++++----
>>   arch/s390/kvm/kvm-s390.h |   13 +++++++++++++
>>   2 files changed, 27 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index fa355a6..4fa3037 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -789,6 +789,19 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
>>   	return ret;
>>   }
>>   
>> +void kvm_s390_vcpu_crypto_reset_all(struct kvm *kvm)
>> + {
>> +	int i;
>> +	struct kvm_vcpu *vcpu;
>> +
>> +	kvm_s390_vcpu_block_all(kvm);
>> +
>> +	kvm_for_each_vcpu(i, vcpu, kvm)
>> +	        kvm_s390_vcpu_crypto_setup(vcpu);
>> +
>> +	kvm_s390_vcpu_unblock_all(kvm);
> This code has to be protected by kvm->lock. Can that be guaranteed by
> the caller?

I can hold the kvm->lock in this function, but if you look at the 
function from which it
is called, kvm_s390_vm_set_crypto(vcpu) below, the kvm->lock is already 
held by that
function to do other work. I suppose the kvm_s390_vm_set_crypto(vcpu) 
instruction could
have released the lock prior to calling 
kvm_s390_vcpu_crypto_reset_all(kvm), but since
this function is called within a block of crypto work, it made sense to 
me to place
the responsibility for locking in the caller and include a comment in 
the comments for
the function definition:

Note: The kvm->lock must be held while calling this function



>
>> +}
>> +
>>   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)
>> @@ -832,10 +845,7 @@ 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..981e3ba 100644
>> --- a/arch/s390/kvm/kvm-s390.h
>> +++ b/arch/s390/kvm/kvm-s390.h
>> @@ -410,4 +410,17 @@ 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 crypt
>> + * attributes and restored to SIE afterward.
>> + *
>> + * Note: The kvm->lock must be held while calling this function
>> + *
>> + * @kvm: the KVM guest
>> + */
>> +void kvm_s390_vcpu_crypto_reset_all(struct kvm *kvm);
>>   #endif
>>
>