[PATCH v2 4/4] KVM: s390: Add KVM capability for ESA mode guests

Eric Farman
2026-04-01T15:12:36Z

From: Hendrik Brueckner <brueckner@linux.ibm.com>

Now that all the bits are properly addressed, provide a mechanism
for testing ESA mode guests in nested configurations.

Signed-off-by: Hendrik Brueckner <brueckner@linux.ibm.com>
[farman@us.ibm.com: Updated commit message]
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
Documentation/virt/kvm/api.rst | 8 ++++++++
arch/s390/kvm/kvm-s390.c | 6 ++++++
include/uapi/linux/kvm.h | 1 +
3 files changed, 15 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 032516783e96..feabfee0f714 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -9436,6 +9436,14 @@ KVM exits with the register state of either the L1 or L2 guest
depending on which executed at the time of an exit. Userspace must
take care to differentiate between these cases.

+8.47 KVM_CAP_S390_VSIE_ESAMODE
+------------------------------
+
+:Architectures: s390
+
+The presence of this capability indicates that the nested KVM guest can
+start in ESA mode.
+
9. Known KVM API problems
=========================

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index d7838334a338..3856af54b6fe 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -629,6 +629,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_IRQFD_RESAMPLE:
case KVM_CAP_S390_USER_OPEREXEC:
case KVM_CAP_S390_KEYOP:
+ case KVM_CAP_S390_VSIE_ESAMODE:
r = 1;
break;
case KVM_CAP_SET_GUEST_DEBUG2:
@@ -926,6 +927,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
icpt_operexc_on_all_vcpus(kvm);
r = 0;
break;
+ case KVM_CAP_S390_VSIE_ESAMODE:
+ VM_EVENT(kvm, 3, "%s", "ENABLE: CAP_S390_VSIE_ESAMODE");
+ kvm->arch.allow_vsie_esamode = 1;
+ r = 0;
+ break;
default:
r = -EINVAL;
break;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 80364d4dbebb..9710184d883d 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -989,6 +989,7 @@ struct kvm_enable_cap {
#define KVM_CAP_ARM_SEA_TO_USER 245
#define KVM_CAP_S390_USER_OPEREXEC 246
#define KVM_CAP_S390_KEYOP 247
+#define KVM_CAP_S390_VSIE_ESAMODE 248

struct kvm_irq_routing_irqchip {
__u32 irqchip;
--
2.51.0