ACK: [I][PATCH 1/1] KVM: s390: Enable specification exception interpretation

[Juerg Haefliger]

On Tue, 14 Sep 2021 07:50:12 +0200
frank.heimes at canonical.com wrote:

> From: Janis Schoetterl-Glausch <scgl at linux.ibm.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1932157
> 
> 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.
> 
> There is no indication if this feature is available or not and the
> hardware is free to interpret or not. So we can simply set this bit and
> if the hardware ignores it we fall back to intercept 8 handling.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl at linux.ibm.com>
> Link: https://lore.kernel.org/linux-s390/20210706114714.3936825-1-scgl@linux.ibm.com/
> Reviewed-by: David Hildenbrand <david at redhat.com>
> Reviewed-by: Christian Borntraeger <borntraeger at de.ibm.com>
> Signed-off-by: Christian Borntraeger <borntraeger at de.ibm.com>
> (cherry picked from commit 7119decf47d9867266459615be502e5d2cecedba)
> Signed-off-by: Frank Heimes <frank.heimes at canonical.com>

Acked-by: Juerg Haefliger <juergh at canonical.com>

...Juerg


> ---
>  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/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 8925f3969478..118d5450c523 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -244,6 +244,7 @@ struct kvm_s390_sie_block {
>  	__u8	fpf;			/* 0x0060 */
>  #define ECB_GS		0x40
>  #define ECB_TE		0x10
> +#define ECB_SPECI	0x08
>  #define ECB_SRSI	0x04
>  #define ECB_HOSTPROTINT	0x02
>  	__u8	ecb;			/* 0x0061 */
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index f72f361d39dd..5b45c83ced21 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -3180,6 +3180,8 @@ 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;
>  
>  	if (test_kvm_facility(vcpu->kvm, 8) && vcpu->kvm->arch.use_pfmfi)
>  		vcpu->arch.sie_block->ecb2 |= ECB2_PFMFI;
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 4002a24bc43a..acda4b6fc851 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -510,6 +510,8 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>  			prefix_unmapped(vsie_page);
>  		scb_s->ecb |= ECB_TE;
>  	}
> +	/* specification exception interpretation */
> +	scb_s->ecb |= scb_o->ecb & ECB_SPECI;
>  	/* branch prediction */
>  	if (test_kvm_facility(vcpu->kvm, 82))
>  		scb_s->fpf |= scb_o->fpf & FPF_BPBC;

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