[RFC 10/33] KVM: x86: hyper-v: Introduce KVM_HV_GET_VSM_STATE

[Nicolas Saenz Julienne <nsaenz@amazon.com>]

HVCALL_GET_VP_REGISTERS exposes the VTL call hypercall page entry
offsets to the guest. This hypercall is implemented in user-space while
the hypercall page patching happens in-kernel. So expose it as part of
the partition wide VSM state.

NOTE: Alternatively there is the option of sharing this information
through a VTL KVM device attribute (the device is introduced in
subsequent patches).

Signed-off-by: Nicolas Saenz Julienne <nsaenz@amazon.com>
---
 arch/x86/include/uapi/asm/kvm.h |  5 +++++
 arch/x86/kvm/hyperv.c           |  8 ++++++++
 arch/x86/kvm/hyperv.h           |  2 ++
 arch/x86/kvm/x86.c              | 18 ++++++++++++++++++
 include/uapi/linux/kvm.h        |  4 ++++
 5 files changed, 37 insertions(+)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index f73d137784d7..370483d5d5fd 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -570,4 +570,9 @@ struct kvm_apic_id_groups {
 	__u8 n_bits; /* nr of bits used to represent group in the APIC ID */
 };
 
+/* for KVM_HV_GET_VSM_STATE */
+struct kvm_hv_vsm_state {
+	__u64 vsm_code_page_offsets;
+};
+
 #endif /* _ASM_X86_KVM_H */
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 2cf430f6ddd8..caaa859932c5 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2990,3 +2990,11 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
 
 	return 0;
 }
+
+int kvm_vm_ioctl_get_hv_vsm_state(struct kvm *kvm, struct kvm_hv_vsm_state *state)
+{
+	struct kvm_hv* hv = &kvm->arch.hyperv;
+
+	state->vsm_code_page_offsets = hv->vsm_code_page_offsets.as_u64;
+	return 0;
+}
diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
index 5433107e7cc8..b3d1113efe82 100644
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -261,4 +261,6 @@ static inline bool kvm_hv_vsm_enabled(struct kvm *kvm)
        return kvm->arch.hyperv.hv_enable_vsm;
 }
 
+int kvm_vm_ioctl_get_hv_vsm_state(struct kvm *kvm, struct kvm_hv_vsm_state *state);
+
 #endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b0512e433032..57f9c58e1e32 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7132,6 +7132,24 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 		r = kvm_vm_ioctl_set_apic_id_groups(kvm, &groups);
 		break;
 	}
+	case KVM_HV_GET_VSM_STATE: {
+		struct kvm_hv_vsm_state vsm_state;
+
+		r = -EINVAL;
+		if (!kvm_hv_vsm_enabled(kvm))
+			goto out;
+
+		r = kvm_vm_ioctl_get_hv_vsm_state(kvm, &vsm_state);
+		if (r)
+			goto out;
+
+		r = -EFAULT;
+		if (copy_to_user(argp, &vsm_state, sizeof(vsm_state)))
+			goto out;
+
+		r = 0;
+		break;
+	}
 	default:
 		r = -ENOTTY;
 	}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 168b6ac6ebe5..03f5c08fd7aa 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -2316,4 +2316,8 @@ struct kvm_create_guest_memfd {
 #define KVM_GUEST_MEMFD_ALLOW_HUGEPAGE		(1ULL << 0)
 
 #define KVM_SET_APIC_ID_GROUPS _IOW(KVMIO, 0xd7, struct kvm_apic_id_groups)
+
+/* Get/Set Hyper-V VSM state. Available with KVM_CAP_HYPERV_VSM */
+#define KVM_HV_GET_VSM_STATE _IOR(KVMIO, 0xd5, struct kvm_hv_vsm_state)
+
 #endif /* __LINUX_KVM_H */
-- 
2.40.1