[PATCH 2/6] KVM: PPC: Introduce KVM_CAP_PPC_COMPAT_CAPS and KVM_PPC_GET_COMPAT_CAPS

[Amit Machhiwal <amachhiw@linux.ibm.com>]

Introduce a new capability and ioctl to expose CPU compatibility modes
supported by the host processor for nested guests.

Introduce a new KVM capability, KVM_CAP_PPC_COMPAT_CAPS, and a
corresponding vm ioctl, KVM_PPC_GET_COMPAT_CAPS, to expose processor
compatibility modes supported by the host.

On IBM POWER systems, newer processor generations (N) can operate in
compatibility modes corresponding to earlier generations, like (N-1) and
(N-2). This is particularly relevant for nested virtualization, where
nested KVM guests may need to run with a specific processor compatibility
level.

The new ioctl returns a bitmap describing the compatibility modes
supported by the host in respective bit numbers. This allows userspace
to select an appropriate compatibility level when configuring nested KVM
guests.

Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
---
 arch/powerpc/include/uapi/asm/kvm.h | 6 ++++++
 include/uapi/linux/kvm.h            | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h
index 077c5437f521..a38dff7a8aea 100644
--- a/arch/powerpc/include/uapi/asm/kvm.h
+++ b/arch/powerpc/include/uapi/asm/kvm.h
@@ -437,6 +437,12 @@ struct kvm_ppc_cpu_char {
 	__u64	behaviour_mask;		/* valid bits in behaviour */
 };
 
+/* For KVM_PPC_GET_COMPAT_CAPS */
+struct kvm_ppc_compat_caps {
+	__u32	flags;
+	__u64	compat_capabilities;	/* Capabilities supported by the host */
+};
+
 /*
  * Values for character and character_mask.
  * These are identical to the values used by H_GET_CPU_CHARACTERISTICS.
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 6c8afa2047bf..1788a0068662 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -996,6 +996,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_S390_USER_OPEREXEC 246
 #define KVM_CAP_S390_KEYOP 247
 #define KVM_CAP_S390_VSIE_ESAMODE 248
+#define KVM_CAP_PPC_COMPAT_CAPS 249
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
@@ -1349,6 +1350,9 @@ struct kvm_s390_keyop {
 #define KVM_GET_DEVICE_ATTR	  _IOW(KVMIO,  0xe2, struct kvm_device_attr)
 #define KVM_HAS_DEVICE_ATTR	  _IOW(KVMIO,  0xe3, struct kvm_device_attr)
 
+/* Available with KVM_CAP_PPC_COMPAT_CAPS */
+#define KVM_PPC_GET_COMPAT_CAPS	_IOR(KVMIO,  0xe4, struct kvm_ppc_compat_caps)
+
 /*
  * ioctls for vcpu fds
  */
-- 
2.50.1