From: Thomas Gleixner Date: Tue, 11 Nov 2025 15:54:36 +0000 (+0100) Subject: ARM: 9459/1: Disable jump-label on PREEMPT_RT X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=256d97d3587b441630c345ab3d773a9e7dcd964b;p=thirdparty%2Fkernel%2Fstable.git 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 Cc: Mark Rutland Cc: Ard Biesheuvel Signed-off-by: Arnd Bergmann Reviewed-by: Linus Walleij Acked-by: Ard Biesheuvel Acked-by: Linus Walleij Reviewed-by: Arnd Bergmann Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Russell King (Oracle) --- diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 2e3f93b690f47..92ca24336ec4b 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