powerpc/ftrace: Add support for livepatch to PPC32

PPC64 needs some special logic to properly set up the TOC.
See commit 85baa095 ("powerpc/livepatch: Add live patching support
on ppc64le") for details.

PPC32 doesn't have TOC so it doesn't need that logic, so adding
LIVEPATCH support is straight forward.

Add CONFIG_LIVEPATCH_64 and move livepatch stack logic into that item.

Livepatch sample modules all work.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/63cb094125b6a6038c65eeac2abaabbabe63addd.1640017960.git.christophe.leroy@csgroup.eu

arch/powerpc/Kconfig

@@ -9,6 +9,10 @@ config 64BIT
 	bool
 	default y if PPC64
 
+config LIVEPATCH_64
+	def_bool PPC64
+	depends	on LIVEPATCH
+
 config MMU
 	bool
 	default y
@@ -221,7 +225,7 @@ config PPC
 	select HAVE_KPROBES_ON_FTRACE
 	select HAVE_KRETPROBES
 	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
-	select HAVE_LIVEPATCH			if HAVE_DYNAMIC_FTRACE_WITH_REGS && PPC64
+	select HAVE_LIVEPATCH			if HAVE_DYNAMIC_FTRACE_WITH_REGS
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_NMI				if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
 	select HAVE_OPTPROBES

arch/powerpc/include/asm/livepatch.h

@@ -23,12 +23,14 @@ static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
 static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
 {
 	/*
-	 * Live patch works only with -mprofile-kernel on PPC. In this case,
-	 * the ftrace location is always within the first 16 bytes.
+	 * Live patch works on PPC32 and only with -mprofile-kernel on PPC64. In
+	 * both cases, the ftrace location is always within the first 16 bytes.
 	 */
 	return ftrace_location_range(faddr, faddr + 16);
 }
+#endif /* CONFIG_LIVEPATCH */
 
+#ifdef CONFIG_LIVEPATCH_64
 static inline void klp_init_thread_info(struct task_struct *p)
 {
 	/* + 1 to account for STACK_END_MAGIC */
@@ -36,6 +38,6 @@ static inline void klp_init_thread_info(struct task_struct *p)
 }
 #else
 static inline void klp_init_thread_info(struct task_struct *p) { }
-#endif /* CONFIG_LIVEPATCH */
+#endif
 
 #endif /* _ASM_POWERPC_LIVEPATCH_H */

arch/powerpc/include/asm/thread_info.h

@@ -51,7 +51,7 @@ struct thread_info {
 	unsigned int	cpu;
 #endif
 	unsigned long	local_flags;		/* private flags for thread */
-#ifdef CONFIG_LIVEPATCH
+#ifdef CONFIG_LIVEPATCH_64
 	unsigned long *livepatch_sp;
 #endif
 #if defined(CONFIG_VIRT_CPU_ACCOUNTING_NATIVE) && defined(CONFIG_PPC32)

arch/powerpc/kernel/asm-offsets.c

@@ -94,7 +94,7 @@ int main(void)
 	OFFSET(TASK_CPU, task_struct, thread_info.cpu);
 #endif
 
-#ifdef CONFIG_LIVEPATCH
+#ifdef CONFIG_LIVEPATCH_64
 	OFFSET(TI_livepatch_sp, thread_info, livepatch_sp);
 #endif