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Subject: Re: [PATCH v10 24/26] KVM: s390: device attrs to enable/disable AP
 interpretation
To:     David Hildenbrand <david@redhat.com>,
        Tony Krowiak <akrowiak@linux.vnet.ibm.com>,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     freude@de.ibm.com, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, borntraeger@de.ibm.com,
        cohuck@redhat.com, kwankhede@nvidia.com,
        bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com,
        alex.williamson@redhat.com, pmorel@linux.vnet.ibm.com,
        alifm@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com,
        jjherne@linux.vnet.ibm.com, thuth@redhat.com,
        pasic@linux.vnet.ibm.com, berrange@redhat.com,
        fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com,
        frankja@linux.ibm.com
References: <1536781396-13601-1-git-send-email-akrowiak@linux.vnet.ibm.com>
 <1536781396-13601-25-git-send-email-akrowiak@linux.vnet.ibm.com>
 <9263b698-1827-1b7f-28bf-75b44657dea2@redhat.com>
 <18a21cda-1da9-3bfb-7b34-80415b5457f9@linux.ibm.com>
 <172560fb-2c54-ea43-3401-f108cf2a0595@redhat.com>
From:   Tony Krowiak <akrowiak@linux.ibm.com>
Date:   Mon, 24 Sep 2018 12:25:12 -0400
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On 09/24/2018 07:23 AM, David Hildenbrand wrote:
> On 22/09/2018 01:40, Tony Krowiak wrote:
>> On 09/17/2018 04:51 AM, David Hildenbrand wrote:
>>> Am 12.09.18 um 21:43 schrieb Tony Krowiak:
>>>> From: Tony Krowiak <akrowiak@linux.ibm.com>
>>>>
>>>> Introduces two new VM crypto device attributes (KVM_S390_VM_CRYPTO)
>>>> to enable or disable AP instruction interpretation from userspace
>>>> via the KVM_SET_DEVICE_ATTR ioctl:
>>>>
>>>> * The KVM_S390_VM_CRYPTO_ENABLE_APIE attribute enables hardware
>>>>     interpretation of AP instructions executed on the guest.
>>>>
>>>> * The KVM_S390_VM_CRYPTO_DISABLE_APIE attribute disables hardware
>>>>     interpretation of AP instructions executed on the guest. In this
>>>>     case the instructions will be intercepted and pass through to
>>>>     the guest.
>>>>
>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>>>> ---
>>>>    arch/s390/include/asm/kvm_host.h |    1 +
>>>>    arch/s390/include/uapi/asm/kvm.h |    2 ++
>>>>    arch/s390/kvm/kvm-s390.c         |   27 +++++++++++++++++++++++----
>>>>    3 files changed, 26 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>>>> index b32bd1b..36d3531 100644
>>>> --- a/arch/s390/include/asm/kvm_host.h
>>>> +++ b/arch/s390/include/asm/kvm_host.h
>>>> @@ -719,6 +719,7 @@ struct kvm_s390_crypto {
>>>>    	__u32 crycbd;
>>>>    	__u8 aes_kw;
>>>>    	__u8 dea_kw;
>>>> +	__u8 apie;
>>>>    };
>>>>    
>>>>    #define APCB0_MASK_SIZE 1
>>>> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
>>>> index 8c23afc..a8dbd90 100644
>>>> --- a/arch/s390/include/uapi/asm/kvm.h
>>>> +++ b/arch/s390/include/uapi/asm/kvm.h
>>>> @@ -161,6 +161,8 @@ struct kvm_s390_vm_cpu_subfunc {
>>>>    #define KVM_S390_VM_CRYPTO_ENABLE_DEA_KW	1
>>>>    #define KVM_S390_VM_CRYPTO_DISABLE_AES_KW	2
>>>>    #define KVM_S390_VM_CRYPTO_DISABLE_DEA_KW	3
>>>> +#define KVM_S390_VM_CRYPTO_ENABLE_APIE		4
>>>> +#define KVM_S390_VM_CRYPTO_DISABLE_APIE		5
>>>>    
>>>>    /* kvm attributes for migration mode */
>>>>    #define KVM_S390_VM_MIGRATION_STOP	0
>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>> index 2cdd980..286c2e0 100644
>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>> @@ -856,12 +856,11 @@ void kvm_s390_vcpu_crypto_reset_all(struct kvm *kvm)
>>>>    
>>>>    static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
>>>>    {
>>>> -	if (!test_kvm_facility(kvm, 76))
>>>> -		return -EINVAL;
>>>> -
>>>>    	mutex_lock(&kvm->lock);
>>>>    	switch (attr->attr) {
>>>>    	case KVM_S390_VM_CRYPTO_ENABLE_AES_KW:
>>>> +		if (!test_kvm_facility(kvm, 76))
>>>> +			return -EINVAL;
>>>>    		get_random_bytes(
>>>>    			kvm->arch.crypto.crycb->aes_wrapping_key_mask,
>>>>    			sizeof(kvm->arch.crypto.crycb->aes_wrapping_key_mask));
>>>> @@ -869,6 +868,8 @@ static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
>>>>    		VM_EVENT(kvm, 3, "%s", "ENABLE: AES keywrapping support");
>>>>    		break;
>>>>    	case KVM_S390_VM_CRYPTO_ENABLE_DEA_KW:
>>>> +		if (!test_kvm_facility(kvm, 76))
>>>> +			return -EINVAL;
>>>>    		get_random_bytes(
>>>>    			kvm->arch.crypto.crycb->dea_wrapping_key_mask,
>>>>    			sizeof(kvm->arch.crypto.crycb->dea_wrapping_key_mask));
>>>> @@ -876,17 +877,31 @@ static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
>>>>    		VM_EVENT(kvm, 3, "%s", "ENABLE: DEA keywrapping support");
>>>>    		break;
>>>>    	case KVM_S390_VM_CRYPTO_DISABLE_AES_KW:
>>>> +		if (!test_kvm_facility(kvm, 76))
>>>> +			return -EINVAL;
>>>>    		kvm->arch.crypto.aes_kw = 0;
>>>>    		memset(kvm->arch.crypto.crycb->aes_wrapping_key_mask, 0,
>>>>    			sizeof(kvm->arch.crypto.crycb->aes_wrapping_key_mask));
>>>>    		VM_EVENT(kvm, 3, "%s", "DISABLE: AES keywrapping support");
>>>>    		break;
>>>>    	case KVM_S390_VM_CRYPTO_DISABLE_DEA_KW:
>>>> +		if (!test_kvm_facility(kvm, 76))
>>>> +			return -EINVAL;
>>>>    		kvm->arch.crypto.dea_kw = 0;
>>>>    		memset(kvm->arch.crypto.crycb->dea_wrapping_key_mask, 0,
>>>>    			sizeof(kvm->arch.crypto.crycb->dea_wrapping_key_mask));
>>>>    		VM_EVENT(kvm, 3, "%s", "DISABLE: DEA keywrapping support");
>>>>    		break;
>>>> +	case KVM_S390_VM_CRYPTO_ENABLE_APIE:
>>>> +		if (!ap_instructions_available()) {
>>>> +			mutex_unlock(&kvm->lock);
>>>> +			return -EOPNOTSUPP;
>>>> +		}
>>>> +		kvm->arch.crypto.apie = 1;
>>>> +		break;
>>>> +	case KVM_S390_VM_CRYPTO_DISABLE_APIE:
>>>> +		kvm->arch.crypto.apie = 0;
>>>> +		break;
>>>>    	default:
>>>>    		mutex_unlock(&kvm->lock);
>>>>    		return -ENXIO;
>>>> @@ -1493,6 +1508,8 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
>>>>    		case KVM_S390_VM_CRYPTO_ENABLE_DEA_KW:
>>>>    		case KVM_S390_VM_CRYPTO_DISABLE_AES_KW:
>>>>    		case KVM_S390_VM_CRYPTO_DISABLE_DEA_KW:
>>>> +		case KVM_S390_VM_CRYPTO_ENABLE_APIE:
>>>> +		case KVM_S390_VM_CRYPTO_DISABLE_APIE:
>>>
>>> As also replied to the QEMU series, could we indicate
>>> KVM_S390_VM_CRYPTO_ENABLE_APIE (and maybe
>>> KVM_S390_VM_CRYPTO_DISABLE_APIE) only with ap_instructions_available(),
>>> so we can avoid the additional KVM_S390_VM_CPU_FEAT_AP?
>>>
>>> KVM_S390_VM_CPU_FEAT_AP is right now completely unused in KVM otherwise
>>> (never checked, we only care about apie).
>>
>> After much discussion with Halil and a few exchanges with you, we
>> decided to go ahead and accept your suggestion to get rid of
>> KVM_S390_VM_CPU_FEAT and keep the VM device attributes to enable/disable
>> apie.
>>
>> To that end, I responded to patches 03/26, 11/26 and 25/26 with fixup!
>> patches that show the KVM/kernel changes that will be necessary to get
>> rid of KVM_S390_VM_CPU_FEAT and use apie to control ECA.28. I did that
>> to generate discussion in v10 rather than waiting until v11 for
>> comments. I make no guarantees that those fixup! patches will
>> successfully apply should you have a v10 branch generated from this
>> patch series you want to update.
>>
> 
> Will you also fixup this patch to expose KVM_S390_VM_CRYPTO_ENABLE_APIE
> only if supported by HW? (ap_instructions_available)

Given that this patch DOES expose KVM_S390_VM_CRYPTO_ENABLE_APIE only if 
supported by HW, I assume you are talking about
KVM_S390_VM_CRYPTO_DISABLE_APIE. I didn't check 
ap_instructions_available() for disabling APIE because I didn't
think it necessary given that ECA.28 will be set to 0 (intercept) by 
default, whether AP instructions are installed or not; so why not allow 
disabling apie. I suppose from the perspective of consistency, since the 
kvm_s390_vm_has_attr() function checks ap_instructions_available() for 
both attributes, then it probably makes sense to add that check to 
KVM_S390_VM_CRYPTO_DISABLE_APIE here. Then again, we could make a change 
in ap_instructions_available() to allow KVM_S390_VM_CRYPTO_DISABLE_APIE 
regardless of whether AP instructions are available. It boils down to 
whether APIE needs to be dynamically disabled at some point when it has 
been enabled. The only case I can think of where that may be necessary 
is if a guest is migrated to a system without AP instructions. I don't 
think that can happen and may even be protected against precisely 
because the VM attributes won't be available on the target system due to 
no AP instructions. What say you?

>