Re: [PATCH v10 24/26] KVM: s390: device attrs to enable/disable AP interpretation

Tony Krowiak
2018-09-24T16:25:12Z

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?

>