From: David Hildenbrand <david@redhat.com>
Date: Thu, 24 Aug 2017 20:51:36 +0200
Subject: KVM: x86: allow setting identity map addr with no vcpus only
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Patch-mainline: v4.15-rc1
Git-commit: 1af1ac910bb3394ac1c0062f5781983dde40a8c0
References: bsc#1077761

Changing it afterwards doesn't make too much sense and will only result
in inconsistencies.

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Acked-by: Alexander Graf <agraf@suse.de>
---
 Documentation/virtual/kvm/api.txt |    1 +
 arch/x86/kvm/x86.c                |    8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1128,6 +1128,7 @@
 because of a quirk in the virtualization implementation (see the internals
 documentation when it pops into existence).
 
+Fails if any VCPU has already been created.
 
 4.41 KVM_SET_BOOT_CPU_ID
 
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4034,10 +4034,16 @@
 	case KVM_SET_IDENTITY_MAP_ADDR: {
 		u64 ident_addr;
 
+		mutex_lock(&kvm->lock);
+		r = -EINVAL;
+		if (kvm->created_vcpus)
+			goto set_identity_unlock;
 		r = -EFAULT;
 		if (copy_from_user(&ident_addr, argp, sizeof ident_addr))
-			goto out;
+			goto set_identity_unlock;
 		r = kvm_vm_ioctl_set_identity_map_addr(kvm, ident_addr);
+set_identity_unlock:
+		mutex_unlock(&kvm->lock);
 		break;
 	}
 	case KVM_SET_NR_MMU_PAGES: