powerpc/ftrace: Remove ftrace init tramp once kernel init is complete

Stop using the ftrace trampoline for init section once kernel init is
complete.

Fixes: 67361cf8071286 ("powerpc/ftrace: Handle large kernel configs")
Cc: [e-mail] # v4.20+
Signed-off-by: Naveen N. Rao <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/include/asm/ftrace.h

···
 #endif /* CONFIG_PPC64_ELF_ABI_V1 */
 #endif /* CONFIG_FTRACE_SYSCALLS */
 
-#ifdef CONFIG_PPC64
+#if defined(CONFIG_PPC64) && defined(CONFIG_FUNCTION_TRACER)
 #include <asm/paca.h>
 
 static inline void this_cpu_disable_ftrace(void)
···
 	return get_paca()->ftrace_enabled;
 }
 
+void ftrace_free_init_tramp(void);
 #else /* CONFIG_PPC64 */
 static inline void this_cpu_disable_ftrace(void) { }
 static inline void this_cpu_enable_ftrace(void) { }
 static inline void this_cpu_set_ftrace_enabled(u8 ftrace_enabled) { }
 static inline u8 this_cpu_get_ftrace_enabled(void) { return 1; }
+static inline void ftrace_free_init_tramp(void) { }
 #endif /* CONFIG_PPC64 */
 #endif /* !__ASSEMBLY__ */
 

arch/powerpc/kernel/trace/ftrace.c

···
 
 	/* Is this a known long jump tramp? */
 	for (i = 0; i < NUM_FTRACE_TRAMPS; i++)
-		if (!ftrace_tramps[i])
-			break;
-		else if (ftrace_tramps[i] == tramp)
+		if (ftrace_tramps[i] == tramp)
 			return 0;
 
 	/* New trampoline -- read where this goes */
···
 #define PACATOC offsetof(struct paca_struct, kernel_toc)
 
 extern unsigned int ftrace_tramp_text[], ftrace_tramp_init[];
+
+void ftrace_free_init_tramp(void)
+{
+	int i;
+
+	for (i = 0; i < NUM_FTRACE_TRAMPS && ftrace_tramps[i]; i++)
+		if (ftrace_tramps[i] == (unsigned long)ftrace_tramp_init) {
+			ftrace_tramps[i] = 0;
+			return;
+		}
+}
 
 int __init ftrace_dyn_arch_init(void)
 {

arch/powerpc/mm/mem.c

···
 #include <asm/kasan.h>
 #include <asm/svm.h>
 #include <asm/mmzone.h>
+#include <asm/ftrace.h>
 #include <asm/code-patching.h>
 
 #include <mm/mmu_decl.h>
···
 	mark_initmem_nx();
 	static_branch_enable(&init_mem_is_free);
 	free_initmem_default(POISON_FREE_INITMEM);
+	ftrace_free_init_tramp();
 }
 
 /*