Messages in this thread | | | Subject | Re: [PATCH] KVM: s390: Enable specification exception interpretation | From | David Hildenbrand <> | Date | Wed, 7 Jul 2021 09:26:56 +0200 |
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On 06.07.21 17:27, Janis Schoetterl-Glausch wrote: > On 7/6/21 5:16 PM, David Hildenbrand wrote: >> 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. > > The bit does get copied for vSIE.
... and I missed that hunk :)
LGTM then
Reviewed-by: David Hildenbrand <david@redhat.com>
-- Thanks,
David / dhildenb
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