linux-kernel - [PATCH 2/5] x86/mm: Use mm_alloc() in poking

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Message-ID: <20221025201057.816175235@infradead.org>
Date:   Tue, 25 Oct 2022 22:06:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, rostedt@...dmis.org,
        dave.hansen@...el.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org, x86@...nel.org,
        keescook@...omium.org, seanjc@...gle.com
Subject: [PATCH 2/5] x86/mm: Use mm_alloc() in poking_init()

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) <peterz@...radead.org>
---
 arch/x86/mm/init.c         |    2 +-
 include/linux/sched/task.h |    1 -
 kernel/fork.c              |    5 -----
 3 files changed, 1 insertion(+), 7 deletions(-)

--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -801,7 +801,7 @@ void __init poking_init(void)
 	spinlock_t *ptl;
 	pte_t *ptep;
 
-	poking_mm = copy_init_mm();
+	poking_mm = mm_alloc();
 	BUG_ON(!poking_mm);
 
 	/*
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -91,7 +91,6 @@ extern void exit_itimers(struct task_str
 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 *);
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2592,11 +2592,6 @@ struct task_struct * __init fork_idle(in
 	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.