[PATCH] powerpc/64: ftrace don't trace real mode

[Nicholas Piggin <npiggin@gmail.com>]

This warns and prevents tracing attempted in a real-mode context.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/trace/ftrace.c            |  3 +++
 .../powerpc/kernel/trace/ftrace_64_mprofile.S | 19 +++++++++++++++----
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 7ea0ca044b65..ef965815fcb9 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -949,6 +949,9 @@ unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
 {
 	unsigned long return_hooker;
 
+	if (WARN_ON_ONCE((mfmsr() & (MSR_IR|MSR_DR)) != (MSR_IR|MSR_DR)))
+		goto out;
+
 	if (unlikely(ftrace_graph_is_dead()))
 		goto out;
 
diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
index f9fd5f743eba..6205f15cb603 100644
--- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
+++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
@@ -51,16 +51,21 @@ _GLOBAL(ftrace_regs_caller)
 	SAVE_10GPRS(12, r1)
 	SAVE_10GPRS(22, r1)
 
-	/* Save previous stack pointer (r1) */
-	addi	r8, r1, SWITCH_FRAME_SIZE
-	std	r8, GPR1(r1)
-
 	/* Load special regs for save below */
 	mfmsr   r8
 	mfctr   r9
 	mfxer   r10
 	mfcr	r11
 
+	/* Shouldn't be called in real mode */
+	andi.	r3,r8,(MSR_IR|MSR_DR)
+	cmpdi	r3,(MSR_IR|MSR_DR)
+	bne	ftrace_bad_realmode
+
+	/* Save previous stack pointer (r1) */
+	addi	r8, r1, SWITCH_FRAME_SIZE
+	std	r8, GPR1(r1)
+
 	/* Get the _mcount() call site out of LR */
 	mflr	r7
 	/* Save it as pt_regs->nip */
@@ -141,6 +146,12 @@ _GLOBAL(ftrace_graph_stub)
 _GLOBAL(ftrace_stub)
 	blr
 
+ftrace_bad_realmode:
+	REST_4GPRS(8, r1)
+#ifdef CONFIG_BUG
+1:	trap
+	EMIT_BUG_ENTRY 1b,__FILE__,__LINE__,(BUGFLAG_WARNING | BUGFLAG_ONCE)
+#endif
 ftrace_no_trace:
 	mflr	r3
 	mtctr	r3
-- 
2.23.0