Messages in this thread | | | Subject | Re: [PATCH] KVM: s390: Enable specification exception interpretation | From | David Hildenbrand <> | Date | Tue, 6 Jul 2021 13:59:51 +0200 |
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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 though HW learned the lesson to always use proper feature indications along with new features)
-- Thanks,
David / dhildenb
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