linux-kernel - [PATCH v4 22/23] powerpc/syscall: Optimise checks in beginning of system_call

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Message-Id: <8d08b80adf3f5aebb3ffc679629bcfa27829bf5a.1611585031.git.christophe.leroy@csgroup.eu>
Date:   Mon, 25 Jan 2021 14:48:35 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, npiggin@...il.com,
        msuchanek@...e.de
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v4 22/23] powerpc/syscall: Optimise checks in beginning of
 system_call_exception()

Combine all tests of regs->msr into a single logical one.

Before the patch:

   0:	81 6a 00 84 	lwz     r11,132(r10)
   4:	90 6a 00 88 	stw     r3,136(r10)
   8:	69 60 00 02 	xori    r0,r11,2
   c:	54 00 ff fe 	rlwinm  r0,r0,31,31,31
  10:	0f 00 00 00 	twnei   r0,0
  14:	69 63 40 00 	xori    r3,r11,16384
  18:	54 63 97 fe 	rlwinm  r3,r3,18,31,31
  1c:	0f 03 00 00 	twnei   r3,0
  20:	69 6b 80 00 	xori    r11,r11,32768
  24:	55 6b 8f fe 	rlwinm  r11,r11,17,31,31
  28:	0f 0b 00 00 	twnei   r11,0

After the patch:

   0:	81 6a 00 84 	lwz     r11,132(r10)
   4:	90 6a 00 88 	stw     r3,136(r10)
   8:	7d 6b 58 f8 	not     r11,r11
   c:	71 6b c0 02 	andi.   r11,r11,49154
  10:	0f 0b 00 00 	twnei   r11,0

6 cycles less on powerpc 8xx (328 => 322 cycles).

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/syscall.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
index a40775daa88b..47ae55f94d1c 100644
--- a/arch/powerpc/kernel/syscall.c
+++ b/arch/powerpc/kernel/syscall.c
@@ -28,6 +28,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
 				   unsigned long r0, struct pt_regs *regs)
 {
 	syscall_fn f;
+	unsigned long expected_msr;
 
 	regs->orig_gpr3 = r3;
 
@@ -39,10 +40,13 @@ notrace long system_call_exception(long r3, long r4, long r5,
 
 	trace_hardirqs_off(); /* finish reconciling */
 
+	expected_msr = MSR_PR;
 	if (!IS_ENABLED(CONFIG_BOOKE) && !IS_ENABLED(CONFIG_40x))
-		BUG_ON(!(regs->msr & MSR_RI));
-	BUG_ON(!(regs->msr & MSR_PR));
-	BUG_ON(arch_irq_disabled_regs(regs));
+		expected_msr |= MSR_RI;
+	if (IS_ENABLED(CONFIG_PPC32))
+		expected_msr |= MSR_EE;
+	BUG_ON((regs->msr & expected_msr) ^ expected_msr);
+	BUG_ON(IS_ENABLED(CONFIG_PPC64) && arch_irq_disabled_regs(regs));
 
 #ifdef CONFIG_PPC_PKEY
 	if (mmu_has_feature(MMU_FTR_PKEY)) {
-- 
2.25.0