diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2025-11-11 16:54:36 +0100 |
|---|---|---|
| committer | Russell King (Oracle) <rmk+kernel@armlinux.org.uk> | 2025-12-02 11:44:55 +0000 |
| commit | 256d97d3587b441630c345ab3d773a9e7dcd964b (patch) | |
| tree | ec5edd5b993cb4db7f2a78b2cc7fb70437e75372 | |
| parent | 3a8660878839faadb4f1a6dd72c3179c1df56787 (diff) | |
ARM: 9459/1: Disable jump-label on PREEMPT_RT
jump-labels are used to efficiently switch between two possible code
paths. To achieve this, stop_machine() is used to keep the CPU in a
known state while the opcode is modified. The usage of stop_machine()
here leads to large latency spikes which can be observed on PREEMPT_RT.
Jump labels may change the target during runtime and are not restricted
to debug or "configuration/ setup" part of a PREEMPT_RT system where
high latencies could be defined as acceptable.
On 64-bit Arm, it is possible to use jump labels without the
stop_machine() call, which architecturally provides a way to atomically
change one 32-bit instruction word while keeping maintaining consistency,
but this is not generally the case on 32-bit, in particular in thumb2
mode.
Disable jump-label support on a PREEMPT_RT system when SMP is enabled.
[bigeasy: Patch description.]
[arnd: add !SMP case, extend changelog]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
| -rw-r--r-- | arch/arm/Kconfig | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 2e3f93b690f4..92ca24336ec4 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -80,7 +80,7 @@ config ARM select HAS_IOPORT select HAVE_ARCH_AUDITSYSCALL if AEABI && !OABI_COMPAT select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6 - select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU + select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU && (!PREEMPT_RT || !SMP) select HAVE_ARCH_KFENCE if MMU && !XIP_KERNEL select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL |