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

[Christian Borntraeger]

On 06.07.21 13:52, Cornelia Huck wrote:
> On Tue, Jul 06 2021, Janis Schoetterl-Glausch <scgl@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > ---
> > 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;