This is a note to let you know that I've just added the patch titled
powerpc/interrupt: Don't read MSR from interrupt_exit_kernel_prepare()
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-interrupt-don-t-read-msr-from-interrupt_exit.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit ae3cf776120039aafd4384d5bb873d11345e77bb
Author: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Date: Mon Jun 5 10:55:26 2023 +0200
powerpc/interrupt: Don't read MSR from interrupt_exit_kernel_prepare()
[ 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@xxxxxxxxxx>
Reviewed-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://msgid.link/df36c6205ab64326fb1b991993c82057e92ace2f.1685955214.git.christophe.leroy@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 8703df709cce8..e93f67c3af76b 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -531,7 +531,6 @@ 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 = current_thread_info()->flags &
@@ -548,7 +547,7 @@ 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. */
