linux-kernel - [PATCH v1 07/22] powerpc/ftrace: Use patch

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Message-Id: <b4505e936e1aee411f7132a27791cf138102f35f.1648131740.git.christophe.leroy@csgroup.eu>
Date:   Thu, 24 Mar 2022 15:29:57 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v1 07/22] powerpc/ftrace: Use patch_instruction() return directly

Instead of returning -EPERM when patch_instruction() fails,
just return what patch_instruction returns.

That simplifies ftrace_modify_code():

	   0:	94 21 ff c0 	stwu    r1,-64(r1)
	   4:	93 e1 00 3c 	stw     r31,60(r1)
	   8:	7c 7f 1b 79 	mr.     r31,r3
	   c:	40 80 00 30 	bge     3c <ftrace_modify_code+0x3c>
	  10:	93 c1 00 38 	stw     r30,56(r1)
	  14:	7c 9e 23 78 	mr      r30,r4
	  18:	7c a4 2b 78 	mr      r4,r5
	  1c:	80 bf 00 00 	lwz     r5,0(r31)
	  20:	7c 1e 28 40 	cmplw   r30,r5
	  24:	40 82 00 34 	bne     58 <ftrace_modify_code+0x58>
	  28:	83 c1 00 38 	lwz     r30,56(r1)
	  2c:	7f e3 fb 78 	mr      r3,r31
	  30:	83 e1 00 3c 	lwz     r31,60(r1)
	  34:	38 21 00 40 	addi    r1,r1,64
	  38:	48 00 00 00 	b       38 <ftrace_modify_code+0x38>
				38: R_PPC_REL24	patch_instruction

Before:

	   0:	94 21 ff c0 	stwu    r1,-64(r1)
	   4:	93 e1 00 3c 	stw     r31,60(r1)
	   8:	7c 7f 1b 79 	mr.     r31,r3
	   c:	40 80 00 4c 	bge     58 <ftrace_modify_code+0x58>
	  10:	93 c1 00 38 	stw     r30,56(r1)
	  14:	7c 9e 23 78 	mr      r30,r4
	  18:	7c a4 2b 78 	mr      r4,r5
	  1c:	80 bf 00 00 	lwz     r5,0(r31)
	  20:	7c 08 02 a6 	mflr    r0
	  24:	90 01 00 44 	stw     r0,68(r1)
	  28:	7c 1e 28 40 	cmplw   r30,r5
	  2c:	40 82 00 48 	bne     74 <ftrace_modify_code+0x74>
	  30:	7f e3 fb 78 	mr      r3,r31
	  34:	48 00 00 01 	bl      34 <ftrace_modify_code+0x34>
				34: R_PPC_REL24	patch_instruction
	  38:	80 01 00 44 	lwz     r0,68(r1)
	  3c:	20 63 00 00 	subfic  r3,r3,0
	  40:	83 c1 00 38 	lwz     r30,56(r1)
	  44:	7c 63 19 10 	subfe   r3,r3,r3
	  48:	7c 08 03 a6 	mtlr    r0
	  4c:	83 e1 00 3c 	lwz     r31,60(r1)
	  50:	38 21 00 40 	addi    r1,r1,64
	  54:	4e 80 00 20 	blr

It improves ftrace activation/deactivation duration by about 3%.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/trace/ftrace.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 98e82fa4980f..1b05d33f96c6 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -78,10 +78,7 @@ ftrace_modify_code(unsigned long ip, ppc_inst_t old, ppc_inst_t new)
 	}
 
 	/* replace the text with the new text */
-	if (patch_instruction((u32 *)ip, new))
-		return -EPERM;
-
-	return 0;
+	return patch_instruction((u32 *)ip, new);
 }
 
 /*
-- 
2.35.1