tomoyo: Use local kmap in tomoyo_dump_page()

Replace the now deprecated kmap_atomic() with kmap_local_page().

The memcpy does not need atomic semantics, and the removed comment
is now stale - this patch now makes it in sync again. Last but not
least, highmem is going to be removed[0].

Link: https://lore.kernel.org/all/4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com/ [0]
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

Author: Davidlohr Bueso

security/tomoyo/domain.c

@@ -934,17 +934,12 @@ bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
 #endif
 	if (page != dump->page) {
 		const unsigned int offset = pos % PAGE_SIZE;
-		/*
-		 * Maybe kmap()/kunmap() should be used here.
-		 * But remove_arg_zero() uses kmap_atomic()/kunmap_atomic().
-		 * So do I.
-		 */
-		char *kaddr = kmap_atomic(page);
+		char *kaddr = kmap_local_page(page);
 
 		dump->page = page;
 		memcpy(dump->data + offset, kaddr + offset,
 		       PAGE_SIZE - offset);
-		kunmap_atomic(kaddr);
+		kunmap_local(kaddr);
 	}
 	/* Same with put_arg_page(page) in fs/exec.c */
 #ifdef CONFIG_MMU