Commit 7119decf authored by Janis Schoetterl-Glausch's avatar Janis Schoetterl-Glausch Committed by Christian Borntraeger
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KVM: s390: Enable specification exception interpretation 



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: default avatarJanis Schoetterl-Glausch <scgl@linux.ibm.com>
Link: https://lore.kernel.org/linux-s390/20210706114714.3936825-1-scgl@linux.ibm.com/


Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
parent 1f703d2c

arch/s390/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -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 */

arch/s390/kvm/kvm-s390.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

arch/s390/kvm/vsie.c

+2 −0
Original line number Diff line number Diff line
@@ -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;