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

David Hildenbrand
2018-09-24T18:46:19Z

On 24/09/2018 18:25, Tony Krowiak wrote:
> 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?
>
>>
>

Just so we're on the same page, I am talking about exposing, I talk
about indicating the attribute:

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 03c23045527f..40924fe05bdf 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1491,6 +1491,11 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm,
struct kvm_device_attr *attr)
case KVM_S390_VM_CRYPTO_DISABLE_DEA_KW:
ret = 0;
break;
+ case KVM_S390_VM_CRYPTO_ENABLE_APIE:
+ case KVM_S390_VM_CRYPTO_DISABLE_APIE:
+ ret = -ENXIO;
+ if (ap_instructions_available())
+ ret = 0;
default:
ret = -ENXIO;
break;

KVM_S390_VM_CRYPTO_DISABLE_APIE can either be handled like
KVM_S390_VM_CRYPTO_ENABLE_APIE (return -EOPNOTSUPP) when setting or
always be allowed. I'll leave that up to you. But as it is completely
useless without ap_instructions_available() /
KVM_S390_VM_CRYPTO_ENABLE_APIE , we might as well also just not expose
it then.

--

Thanks,

David / dhildenb