Add a macro mechanism that generates an opt-in and arch-namespaced
file_to_kvm_<arch>() to convert a file reference to a kvm object if the
file handle represents a kvm handle.

Activate for x86 and for s390 (native KVM only).

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
---
 arch/s390/include/asm/kvm_host_s390.h |  2 ++
 arch/x86/include/asm/kvm_host.h       |  2 ++
 arch/x86/kvm/Makefile                 |  1 +
 include/linux/kvm_host.h              | 12 ++++++++++++
 virt/kvm/kvm_main.c                   | 11 +++++++++++
 5 files changed, 28 insertions(+)

diff --git a/arch/s390/include/asm/kvm_host_s390.h b/arch/s390/include/asm/kvm_host_s390.h
index cd692f8fb764..8a7eed5847e1 100644
--- a/arch/s390/include/asm/kvm_host_s390.h
+++ b/arch/s390/include/asm/kvm_host_s390.h
@@ -27,6 +27,8 @@
 #include <asm/isc.h>
 #include <asm/guarded_storage.h>
 
+#define kvm_file_to_kvm_arch s390
+
 #define KVM_HAVE_MMU_RWLOCK
 #define KVM_MAX_VCPUS 255
 
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 683bb8bf43a9..e460073ff176 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -44,6 +44,8 @@
 
 #include <hyperv/hvhdk.h>
 
+#define kvm_file_to_kvm_arch x86
+
 #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
 
 /*
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index 0474604ab8a1..e6d395ede9e2 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -61,6 +61,7 @@ exports_grep_trailer := --include='*.[ch]' -nrw $(srctree)/virt/kvm $(srctree)/a
 				-e kvm_page_track_unregister_notifier \
 				-e kvm_write_track_add_gfn \
 				-e kvm_write_track_remove_gfn \
+				-e kvm_file_to_kvm_fn \
 				-e kvm_get_kvm \
 				-e kvm_get_kvm_safe \
 				-e kvm_put_kvm
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index cf7fe835c4ad..bc3abfde8393 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1082,6 +1082,18 @@ void kvm_get_kvm(struct kvm *kvm);
 bool kvm_get_kvm_safe(struct kvm *kvm);
 void kvm_put_kvm(struct kvm *kvm);
 bool file_is_kvm(struct file *file);
+
+/*
+ * Architectures define kvm_file_to_kvm_arch to <arch>
+ * to get a typed, arch-namespaced helper:
+ *
+ *   struct kvm *file_to_kvm_<arch>(struct file *file)
+ */
+#ifdef kvm_file_to_kvm_arch
+#define kvm_file_to_kvm_fn CONCATENATE(file_to_kvm_, kvm_file_to_kvm_arch)
+struct kvm *kvm_file_to_kvm_fn(struct file *file);
+#endif /* kvm_file_to_kvm_arch */
+
 void kvm_put_kvm_no_destroy(struct kvm *kvm);
 
 static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 85f42289748d..07fc874a38e1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5519,6 +5519,17 @@ bool file_is_kvm(struct file *file)
 }
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(file_is_kvm);
 
+#ifdef kvm_file_to_kvm_arch
+struct kvm *kvm_file_to_kvm_fn(struct file *file)
+{
+	if (!file || file->f_op != &kvm_vm_fops)
+		return NULL;
+
+	return file->private_data;
+}
+EXPORT_SYMBOL_GPL(kvm_file_to_kvm_fn);
+#endif
+
 static int kvm_dev_ioctl_create_vm(unsigned long type)
 {
 	char fdname[ITOA_MAX_LEN + 1];

-- 
2.53.0