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

[frank.heimes at canonical.com]

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>
---
 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;
-- 
2.25.1