Messages in this thread | | | Subject | Re: [PATCH] KVM: s390: Enable specification exception interpretation | From | David Hildenbrand <> | Date | Tue, 6 Jul 2021 17:16:17 +0200 |
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On 06.07.21 14:02, Christian Borntraeger wrote: > > > On 06.07.21 13:59, David Hildenbrand wrote: >> On 06.07.21 13:56, Christian Borntraeger wrote: >>> >>> >>> 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). >> >> I remember the architecture said at some point to never set undefined bits - and this bit is undefined on older HW generations. I might be wrong, though. > > I can confirm that this bit will be ignored on older machines. The notion of > never setting undefined bits comes from "you never know what this bit will > change in future machines". Now we know :-)
Well, okay then :)
So the plan for vSIE is to always keep it disabled? IIUC, one could similarly always forward the bit of set.
-- Thanks,
David / dhildenb
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