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Date: Tue, 17 Apr 2018 18:55:08 +0200
From: Pierre Morel <pmorel@...ux.vnet.ibm.com>
To: Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, buendgen@...ibm.com
Cc: freude@...ibm.com, schwidefsky@...ibm.com,
heiko.carstens@...ibm.com, borntraeger@...ibm.com,
cohuck@...hat.com, kwankhede@...dia.com,
bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
alex.williamson@...hat.com, alifm@...ux.vnet.ibm.com,
mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
thuth@...hat.com, pasic@...ux.vnet.ibm.com, berrange@...hat.com,
fiuczy@...ux.vnet.ibm.com
Subject: Re: [PATCH v4 05/15] KVM: s390: enable/disable AP interpretive
execution
On 17/04/2018 18:22, Tony Krowiak wrote:
> On 04/17/2018 12:13 PM, Pierre Morel wrote:
>> On 17/04/2018 17:02, Tony Krowiak wrote:
>>> On 04/16/2018 06:51 AM, Pierre Morel wrote:
>>>> On 15/04/2018 23:22, Tony Krowiak wrote:
>>>>> The VFIO AP device model exploits interpretive execution of AP
>>>>> instructions (APIE) to provide guests passthrough access to AP
>>>>> devices. This patch introduces a new interface to enable and
>>>>> disable APIE.
>>>>>
>>>>> Signed-off-by: Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
>>>>> ---
>>>>> arch/s390/include/asm/kvm-ap.h | 16 ++++++++++++++++
>>>>> arch/s390/include/asm/kvm_host.h | 1 +
>>>>> arch/s390/kvm/kvm-ap.c | 20 ++++++++++++++++++++
>>>>> arch/s390/kvm/kvm-s390.c | 9 +++++++++
>>>>> 4 files changed, 46 insertions(+), 0 deletions(-)
>>>>>
>>>>> diff --git a/arch/s390/include/asm/kvm-ap.h
>>>>> b/arch/s390/include/asm/kvm-ap.h
>>>>> index 736e93e..a6c092e 100644
>>>>> --- a/arch/s390/include/asm/kvm-ap.h
>>>>> +++ b/arch/s390/include/asm/kvm-ap.h
>>>>> @@ -35,4 +35,20 @@
>>>>> */
>>>>> void kvm_ap_build_crycbd(struct kvm *kvm);
>>>>>
>>>>> +/**
>>>>> + * kvm_ap_interpret_instructions
>>>>> + *
>>>>> + * Indicate whether AP instructions shall be interpreted. If they
>>>>> are not
>>>>> + * interpreted, all AP instructions will be intercepted and
>>>>> routed back to
>>>>> + * userspace.
>>>>> + *
>>>>> + * @kvm: the virtual machine attributes
>>>>> + * @enable: indicates whether AP instructions are to be
>>>>> interpreted (true) or
>>>>> + * or not (false).
>>>>> + *
>>>>> + * Returns 0 if completed successfully; otherwise, returns
>>>>> -EOPNOTSUPP
>>>>> + * indicating that AP instructions are not installed on the guest.
>>>>> + */
>>>>> +int kvm_ap_interpret_instructions(struct kvm *kvm, bool enable);
>>>>> +
>>>>> #endif /* _ASM_KVM_AP */
>>>>> diff --git a/arch/s390/include/asm/kvm_host.h
>>>>> b/arch/s390/include/asm/kvm_host.h
>>>>> index 3162783..5470685 100644
>>>>> --- a/arch/s390/include/asm/kvm_host.h
>>>>> +++ b/arch/s390/include/asm/kvm_host.h
>>>>> @@ -715,6 +715,7 @@ struct kvm_s390_crypto {
>>>>> __u32 crycbd;
>>>>> __u8 aes_kw;
>>>>> __u8 dea_kw;
>>>>> + __u8 apie;
>>>>> };
>>>>>
>>>>> #define APCB0_MASK_SIZE 1
>>>>> diff --git a/arch/s390/kvm/kvm-ap.c b/arch/s390/kvm/kvm-ap.c
>>>>> index 991bae4..55d11b5 100644
>>>>> --- a/arch/s390/kvm/kvm-ap.c
>>>>> +++ b/arch/s390/kvm/kvm-ap.c
>>>>> @@ -58,3 +58,23 @@ void kvm_ap_build_crycbd(struct kvm *kvm)
>>>>> }
>>>>> }
>>>>> EXPORT_SYMBOL(kvm_ap_build_crycbd);
>>>>> +
>>>>> +int kvm_ap_interpret_instructions(struct kvm *kvm, bool enable)
>>>>> +{
>>>>> + int ret = 0;
>>>>> +
>>>>> + mutex_lock(&kvm->lock);
>>>>> +
>>>>> + if (!test_kvm_cpu_feat(kvm, KVM_S390_VM_CPU_FEAT_AP)) {
>>>>
>>>> Do we really need to test CPU_FEAT_AP?
>>>
>>> Yes we do.
>>
>> really? why?
>
> The KVM_S390_VM_CPU_FEAT_AP will not be enabled by KVM if the AP
> instructions are not installed on the host. I assume - but have
> no way of verifying - that if the AP instructions are not installed
> on the host, that interpretation would fail. Do you know what would
> happen if AP instructions are interpreted when not installed on
> the host?
If the host has no AP instructions (his ECA.28=0) but it set ECA.28 for
a guest,
there will be no AP instructions available in the guest.
>
>>
>>
>>>
>>>>
>>>>
>>>> I understand that KVM_S390_VM_CPU_FEAT_AP means AP instructions are
>>>> interpreted.
>>>> shouldn't we add this information in the name?
>>>> like KVM_S390_VM_CPU_FEAT_APIE
>>>
>>> KVM_S390_VM_CPU_FEAT_AP does NOT mean AP instructions are
>>> interpreted, it means
>>> AP instructions are installed.
>>
>> Right same error I made all along this review.
>> But AFAIK it means AP instructions are provided to the guest.
>> Then should this function be called if the guest has no AP
>> instructions ?
>>
>>
>>>
>>>>
>>>>> + ret = -EOPNOTSUPP;
>>>>> + goto done;
>>>>> + }
>>>>> +
>>>>> + kvm->arch.crypto.apie = enable;
>>>>> + kvm_s390_vcpu_crypto_reset_all(kvm);
>>>>> +
>>>>> +done:
>>>>> + mutex_unlock(&kvm->lock);
>>>>> + return ret;
>>>>> +}
>>>>> +EXPORT_SYMBOL(kvm_ap_interpret_instructions);
>>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>>> index 55cd897..1dc8566 100644
>>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>>> @@ -1901,6 +1901,9 @@ static void kvm_s390_crypto_init(struct kvm
>>>>> *kvm)
>>>>> kvm->arch.crypto.crycb = &kvm->arch.sie_page2->crycb;
>>>>> kvm_ap_build_crycbd(kvm);
>>>>>
>>>>> + /* Default setting indicating SIE shall interpret AP
>>>>> instructions */
>>>>> + kvm->arch.crypto.apie = 1;
>>>>> +
>>>>> if (!test_kvm_facility(kvm, 76))
>>>>> return;
>>>>>
>>>>> @@ -2434,6 +2437,12 @@ static void
>>>>> kvm_s390_vcpu_crypto_setup(struct kvm_vcpu *vcpu)
>>>>> {
>>>>> vcpu->arch.sie_block->crycbd = vcpu->kvm->arch.crypto.crycbd;
>>>>>
>>>>> + vcpu->arch.sie_block->eca &= ~ECA_APIE;
>>>>> + if (vcpu->kvm->arch.crypto.apie &&
>>>>> + test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_AP))
>>>>
>>>> Do we call xxx_crypto_setup() if KVM does not support AP
>>>> interpretation?
>>>
>>> Yes, kvm_s390_vcpu_crypto_setup(vcpu) is called by
>>> kvm_arch_vcpu_setup(vcpu)
>>> as well as from kvm_s390_vcpu_crypto_reset_all(kvm). Calling it has
>>> nothing
>>> to do with whether AP interpretation is supported or not as it does
>>> much
>>> more than that, including setting up of wrapping keys and the CRYCBD.
>>
>> Sorry, still the same error I made about CPU_FEAT_AP meaning AP
>> instructions in the guest
>> and not AP interpretation available.
>> Could apie be set if AP instruction are not supported?
>>
>>>
>>>>
>>>>> + vcpu->arch.sie_block->eca |= ECA_APIE;
>>>>> +
>>>>> +
>>>>> if (!test_kvm_facility(vcpu->kvm, 76))
>>>>> return;
>>>>>
>>>>
>>>
>>
>
--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany
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