releases/6.3.13/powerpc-interrupt-don-t-read-msr-from-interrupt_exit.patch

From 52aa157018e9a44bda2a5d5b0c30f1fe73a74ea8 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Mon, 5 Jun 2023 10:55:26 +0200
Subject: powerpc/interrupt: Don't read MSR from
 interrupt_exit_kernel_prepare()

From: Christophe Leroy <christophe.leroy@csgroup.eu>

[ Upstream commit 0eb089a72fda3f7969e6277804bde75dc1474a14 ]

A disassembly of interrupt_exit_kernel_prepare() shows a useless read
of MSR register. This is shown by r9 being re-used immediately without
doing anything with the value read.

  c000e0e0:       60 00 00 00     nop
  c000e0e4:       7d 3a c2 a6     mfmd_ap r9
  c000e0e8:       7d 20 00 a6     mfmsr   r9
  c000e0ec:       7c 51 13 a6     mtspr   81,r2
  c000e0f0:       81 3f 00 84     lwz     r9,132(r31)
  c000e0f4:       71 29 80 00     andi.   r9,r9,32768

This is due to the use of local_irq_save(). The flags read by
local_irq_save() are never used, use local_irq_disable() instead.

Fixes: 13799748b957 ("powerpc/64: use interrupt restart table to speed up return from interrupt")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/df36c6205ab64326fb1b991993c82057e92ace2f.1685955214.git.christophe.leroy@csgroup.eu
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/powerpc/kernel/interrupt.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 0ec1581619db5..cf770d86c03c6 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -368,7 +368,6 @@ void preempt_schedule_irq(void);
 
 notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
 {
-	unsigned long flags;
 	unsigned long ret = 0;
 	unsigned long kuap;
 	bool stack_store = read_thread_flags() & _TIF_EMULATE_STACK_STORE;
@@ -392,7 +391,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
 
 	kuap = kuap_get_and_assert_locked();
 
-	local_irq_save(flags);
+	local_irq_disable();
 
 	if (!arch_irq_disabled_regs(regs)) {
 		/* Returning to a kernel context with local irqs enabled. */
-- 
2.39.2