x86/mm: Use mm_alloc() in poking_init()

commit 3f4c821 upstream.

Instead of duplicating init_mm, allocate a fresh mm. The advantage is
that mm_alloc() has much simpler dependencies. Additionally it makes
more conceptual sense, init_mm has no (and must not have) user state
to duplicate.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Peter Zijlstra

arch/x86/mm/init.c

@@ -827,7 +827,7 @@ void __init poking_init(void)
 	spinlock_t *ptl;
 	pte_t *ptep;
 
-	poking_mm = copy_init_mm();
+	poking_mm = mm_alloc();
 	BUG_ON(!poking_mm);
 
 	/* Xen PV guests need the PGD to be pinned. */

include/linux/sched/task.h

@@ -90,7 +90,6 @@ extern void exit_itimers(struct task_struct *);
 extern pid_t kernel_clone(struct kernel_clone_args *kargs);
 struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node);
 struct task_struct *fork_idle(int);
-struct mm_struct *copy_init_mm(void);
 extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
 extern pid_t user_mode_thread(int (*fn)(void *), void *arg, unsigned long flags);
 extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);

kernel/fork.c

@@ -2600,11 +2600,6 @@ struct task_struct * __init fork_idle(int cpu)
 	return task;
 }
 
-struct mm_struct *copy_init_mm(void)
-{
-	return dup_mm(NULL, &init_mm);
-}
-
 /*
  * This is like kernel_clone(), but shaved down and tailored to just
  * creating io_uring workers. It returns a created task, or an error pointer.