Re: [PATCH] KVM: s390: Enable specification exception interpretation

Christian Borntraeger
2021-07-06T12:03:46Z

On 06.07.21 13:52, Cornelia Huck wrote:
> On Tue, Jul 06 2021, Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote:
>
>> When this feature is enabled the hardware is free to interpret
>> specification exceptions generated by the guest, instead of causing
>> program interruption interceptions.
>>
>> This benefits (test) programs that generate a lot of specification
>> exceptions (roughly 4x increase in exceptions/sec).
>>
>> Interceptions will occur as before if ICTL_PINT is set,
>> i.e. if guest debug is enabled.
>>
>> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
>> ---
>> I'll additionally send kvm-unit-tests for testing this feature.
>>
>> arch/s390/include/asm/kvm_host.h | 1 +
>> arch/s390/kvm/kvm-s390.c | 2 ++
>> arch/s390/kvm/vsie.c | 2 ++
>> 3 files changed, 5 insertions(+)
>
> (...)
>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index b655a7d82bf0..aadd589a3755 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -3200,6 +3200,8 @@ static int kvm_s390_vcpu_setup(struct kvm_vcpu *vcpu)
>> vcpu->arch.sie_block->ecb |= ECB_SRSI;
>> if (test_kvm_facility(vcpu->kvm, 73))
>> vcpu->arch.sie_block->ecb |= ECB_TE;
>> + if (!kvm_is_ucontrol(vcpu->kvm))
>> + vcpu->arch.sie_block->ecb |= ECB_SPECI;
>
> Does this exist for any hardware version (i.e. not guarded by a cpu
> feature?)

Not for all hardware versions, but also no indication. The architecture
says that the HW is free to do this or not. (which makes the vsie code
simpler).
>
>>
>> if (test_kvm_facility(vcpu->kvm, 8) && vcpu->kvm->arch.use_pfmfi)
>> vcpu->arch.sie_block->ecb2 |= ECB2_PFMFI;
>