Message-ID: <aLsZ9S3X0OpKy1RM@antec>
Date: Fri, 5 Sep 2025 18:12:21 +0100
From: Stafford Horne <shorne@...il.com>
To: ChenMiao <chenmiao.ku@...il.com>
Cc: Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux OpenRISC <linux-openrisc@...r.kernel.org>,
	Jonathan Corbet <corbet@....net>, Jonas Bonn <jonas@...thpole.se>,
	Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Jason Baron <jbaron@...mai.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Johannes Berg <johannes@...solutions.net>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	Sahil Siddiq <sahilcdq0@...il.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 4/4] openrisc: Add jump label support

On Thu, Sep 04, 2025 at 10:00:52AM +0000, ChenMiao wrote:
> From: chenmiao <chenmiao.ku@...il.com>
> 
> Supported a complete jump_label implementation based on the ARM64 and
> RV64 version and add the CONFIG_JUMP_LABEL=y to the defconfig.
> 
> Testing was conducted using a dedicated test module (jump-label-test,
> provided in the link below) with the following environment: Below is
> a brief usage and test report of this module. For detailed steps,
> please refer to the README in the provided link.

Maybe you can shorten to:

    Testing was conducted using a dedicated test module jump-label-test,
    provided in the link below. For detailed steps, please refer to the
    README also at the provided link.

> Link: https://github.com/ChenMiaoi/GSoC-2025-Final-Report/tree/main/tests/jump-label-test
> 
> Test Environment:
>   - Hardware: QEMU emulated OR1K
>   - Kernel Version: 6.17.0-rc3-dirty
>   - Configs: CONFIG_MODULES=y,CONFIG_MODULE_UNLOAD=y
>   - Toolchain: or1k-none-linux-musl-gcc 15.1.0
> 
> Test Procedure:
>   1. Build and install modules (make modules_install)
>   2. Build the jump-label-test module
>   3. Boot kernel in QEMU
>   4. Transfer jump_label_test.ko via NFS
>   5. Load module and observe results

The procedure is in the readme, maybe its not needed here.

> Test Results:
> $ insmod jump_label_test.ko
> [   32.590000] Jump label performance test module loaded
> [   35.250000] Normal branch time: 1241327150 ns (124 ns per iteration)
> [   35.250000] Jump label (false) time: 706422700 ns (70 ns per iteration)
> [   35.250000] Jump label (true) time: 708913450 ns (70 ns per iteration)
> $ rmmod jump_label_test.ko
> [   72.210000] Jump label test module unloaded
> 
> The results show approximately 43% improvement in branch performance
> when using jump labels compared to traditional branches.

This is good.

> Link: https://lore.kernel.org/openrisc/aK3O6kOMqgDb6zZj@antec/T/#u
> Signed-off-by: chenmiao <chenmiao.ku@...il.com>
> 
> ---
> Changes in V4:
>   - Add appropriate comments.
>   - Added testing for jump_label
> 
> Changes in V3:
>   - Ensure the two defconfig using the make savedefconfig.
>   - modify the __ASSEMBLY__ to __ASSEMBLER__, modify the
>     __ASM_JUMP_LABEL_H to __ASM_OPENRISC_JUMP_LABEL_H and remove
>     invalid comment.
> 
> Changes in V2:
>   - using the patch_insn_write(void *addr, u32 insn) not the
>     const void *insn.
>   - add new macro OPENRISC_INSN_NOP in insn-def.h to use.
> 
> Signed-off-by: chenmiao <chenmiao.ku@...il.com>
> ---
>  .../core/jump-labels/arch-support.txt         |  2 +-
>  arch/openrisc/Kconfig                         |  2 +
>  arch/openrisc/configs/or1ksim_defconfig       |  1 +
>  arch/openrisc/configs/virt_defconfig          |  1 +
>  arch/openrisc/include/asm/insn-def.h          |  3 +
>  arch/openrisc/include/asm/jump_label.h        | 72 +++++++++++++++++++
>  arch/openrisc/kernel/Makefile                 |  1 +
>  arch/openrisc/kernel/jump_label.c             | 52 ++++++++++++++
>  arch/openrisc/kernel/setup.c                  |  2 +
>  9 files changed, 135 insertions(+), 1 deletion(-)
>  create mode 100644 arch/openrisc/include/asm/jump_label.h
>  create mode 100644 arch/openrisc/kernel/jump_label.c
> 
> diff --git a/Documentation/features/core/jump-labels/arch-support.txt b/Documentation/features/core/jump-labels/arch-support.txt
> index ccada815569f..683de7c15058 100644
> --- a/Documentation/features/core/jump-labels/arch-support.txt
> +++ b/Documentation/features/core/jump-labels/arch-support.txt
> @@ -17,7 +17,7 @@
>      |  microblaze: | TODO |
>      |        mips: |  ok  |
>      |       nios2: | TODO |
> -    |    openrisc: | TODO |
> +    |    openrisc: |  ok  |
>      |      parisc: |  ok  |
>      |     powerpc: |  ok  |
>      |       riscv: |  ok  |
> diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
> index b38fee299bc4..9156635dd264 100644
> --- a/arch/openrisc/Kconfig
> +++ b/arch/openrisc/Kconfig
> @@ -24,6 +24,8 @@ config OPENRISC
>  	select GENERIC_PCI_IOMAP
>  	select GENERIC_IOREMAP
>  	select GENERIC_CPU_DEVICES
> +	select HAVE_ARCH_JUMP_LABEL
> +	select HAVE_ARCH_JUMP_LABEL_RELATIVE
>  	select HAVE_PCI
>  	select HAVE_UID16
>  	select HAVE_PAGE_SIZE_8KB
> diff --git a/arch/openrisc/configs/or1ksim_defconfig b/arch/openrisc/configs/or1ksim_defconfig
> index 58e27d8fdb4e..769705ac24d5 100644
> --- a/arch/openrisc/configs/or1ksim_defconfig
> +++ b/arch/openrisc/configs/or1ksim_defconfig
> @@ -10,6 +10,7 @@ CONFIG_EXPERT=y
>  # CONFIG_KALLSYMS is not set
>  CONFIG_BUILTIN_DTB_NAME="or1ksim"
>  CONFIG_HZ_100=y
> +CONFIG_JUMP_LABEL=y
>  CONFIG_MODULES=y
>  # CONFIG_BLOCK is not set
>  CONFIG_SLUB_TINY=y
> diff --git a/arch/openrisc/configs/virt_defconfig b/arch/openrisc/configs/virt_defconfig
> index 8a581e932766..a93a3e1e4f87 100644
> --- a/arch/openrisc/configs/virt_defconfig
> +++ b/arch/openrisc/configs/virt_defconfig
> @@ -12,6 +12,7 @@ CONFIG_NR_CPUS=8
>  CONFIG_SMP=y
>  CONFIG_HZ_100=y
>  # CONFIG_OPENRISC_NO_SPR_SR_DSX is not set
> +CONFIG_JUMP_LABEL=y
>  # CONFIG_COMPAT_BRK is not set
>  CONFIG_NET=y
>  CONFIG_PACKET=y
> diff --git a/arch/openrisc/include/asm/insn-def.h b/arch/openrisc/include/asm/insn-def.h
> index e28a9a9604fc..1e0c028a5b95 100644
> --- a/arch/openrisc/include/asm/insn-def.h
> +++ b/arch/openrisc/include/asm/insn-def.h
> @@ -9,4 +9,7 @@
>  /* or1k instructions are always 32 bits. */
>  #define	OPENRISC_INSN_SIZE		4
>  
> +/* or1k nop instruction code */
> +#define OPENRISC_INSN_NOP     0x15000000U
> +
>  #endif /* __ASM_OPENRISC_INSN_DEF_H */
> diff --git a/arch/openrisc/include/asm/jump_label.h b/arch/openrisc/include/asm/jump_label.h
> new file mode 100644
> index 000000000000..3ec0f4e19f9c
> --- /dev/null
> +++ b/arch/openrisc/include/asm/jump_label.h
> @@ -0,0 +1,72 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2025 Chen Miao
> + *
> + * Based on arch/arm/include/asm/jump_label.h
> + */
> +#ifndef __ASM_OPENRISC_JUMP_LABEL_H
> +#define __ASM_OPENRISC_JUMP_LABEL_H
> +
> +#ifndef __ASSEMBLER__
> +
> +#include <linux/types.h>
> +#include <asm/insn-def.h>
> +
> +#define HAVE_JUMP_LABEL_BATCH
> +
> +#define JUMP_LABEL_NOP_SIZE OPENRISC_INSN_SIZE
> +
> +/**
> + * JUMP_TABLE_ENTRY - Create a jump table entry
> + * @key: Jump key identifier (typically a symbol address)
> + * @label: Target label address
> + *
> + * This macro creates a jump table entry in the dedicated kernel section (__jump_table).
> + * Each entry contains the following information:
> + * 		Offset from current instruction to jump instruction (1b - .)
> + * 		Offset from current instruction to target label (label - .)
> + * 		Offset from current instruction to key identifier (key - .)
> + */
> +#define JUMP_TABLE_ENTRY(key, label)			\
> +	".pushsection	__jump_table, \"aw\"	\n\t"	\
> +	".align 	4 			\n\t"	\
> +	".long 		1b - ., " label " - .	\n\t"	\
> +	".long 		" key " - . 		\n\t"	\
> +	".popsection				\n\t"
> +
> +#define ARCH_STATIC_BRANCH_ASM(key, label)		\
> +	".align		4			\n\t"	\
> +	"1: l.nop				\n\t"	\
> +	"    l.nop				\n\t"	\
> +	JUMP_TABLE_ENTRY(key, label)
> +
> +static __always_inline bool arch_static_branch(struct static_key *const key,
> +					       const bool branch)
> +{
> +	asm goto (ARCH_STATIC_BRANCH_ASM("%0", "%l[l_yes]")
> +		  ::"i"(&((char *)key)[branch])::l_yes);
> +
> +	return false;
> +l_yes:
> +	return true;
> +}
> +
> +#define ARCH_STATIC_BRANCH_JUMP_ASM(key, label)		\
> +	".align		4			\n\t"	\
> +	"1: l.j	" label "			\n\t"	\
> +	"    l.nop				\n\t"	\
> +	JUMP_TABLE_ENTRY(key, label)
> +
> +static __always_inline bool
> +arch_static_branch_jump(struct static_key *const key, const bool branch)
> +{
> +	asm goto (ARCH_STATIC_BRANCH_JUMP_ASM("%0", "%l[l_yes]")
> +		  ::"i"(&((char *)key)[branch])::l_yes);
> +
> +	return false;
> +l_yes:
> +	return true;
> +}
> +
> +#endif /* __ASSEMBLER__ */
> +#endif /* __ASM_OPENRISC_JUMP_LABEL_H */
> diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile
> index f0957ce16d6b..19e0eb94f2eb 100644
> --- a/arch/openrisc/kernel/Makefile
> +++ b/arch/openrisc/kernel/Makefile
> @@ -9,6 +9,7 @@ obj-y	:= head.o setup.o or32_ksyms.o process.o dma.o \
>  	   traps.o time.o irq.o entry.o ptrace.o signal.o \
>  	   sys_call_table.o unwinder.o cacheinfo.o
>  
> +obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
>  obj-$(CONFIG_SMP)		+= smp.o sync-timer.o
>  obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
>  obj-$(CONFIG_MODULES)		+= module.o
> diff --git a/arch/openrisc/kernel/jump_label.c b/arch/openrisc/kernel/jump_label.c
> new file mode 100644
> index 000000000000..071dacad885c
> --- /dev/null
> +++ b/arch/openrisc/kernel/jump_label.c
> @@ -0,0 +1,52 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2025 Chen Miao
> + *
> + * Based on arch/arm/kernel/jump_label.c
> + */
> +#include <linux/jump_label.h>
> +#include <linux/kernel.h>
> +#include <linux/memory.h>
> +#include <asm/bug.h>
> +#include <asm/cacheflush.h>
> +#include <asm/text-patching.h>
> +
> +bool arch_jump_label_transform_queue(struct jump_entry *entry,
> +				     enum jump_label_type type)
> +{
> +	void *addr = (void *)jump_entry_code(entry);
> +	u32 insn;
> +
> +	if (type == JUMP_LABEL_JMP) {
> +		long offset;
> +
> +		offset = jump_entry_target(entry) - jump_entry_code(entry);
> +		/*
> +		 * The actual maximum range of the l.j instruction's offset is -134,217,728
> +		 * ~ 134,217,724 (sign 26-bit imm).
> +		 * For the original jump range, we need to right-shift N by 2 to obtain the
> +		 * instruction's offset.
> +		 */
> +		if (unlikely(offset < -134217728 || offset > 134217724)) {
> +			WARN_ON_ONCE(true);
> +		}
> +		/* 26bit imm mask */
> +		offset = (offset >> 2) & 0x03ffffff;
> +
> +		insn = offset;
> +	} else {
> +		insn = OPENRISC_INSN_NOP;
> +	}
> +
> +	if (early_boot_irqs_disabled) {
> +		copy_to_kernel_nofault(addr, &insn, sizeof(insn));
> +	} else {
> +		patch_insn_write(addr, insn);
> +	}
> +	return true;
> +}
> +
> +void arch_jump_label_transform_apply(void)
> +{
> +	kick_all_cpus_sync();
> +}
> diff --git a/arch/openrisc/kernel/setup.c b/arch/openrisc/kernel/setup.c
> index a9fb9cc6779e..000a9cc10e6f 100644
> --- a/arch/openrisc/kernel/setup.c
> +++ b/arch/openrisc/kernel/setup.c
> @@ -249,6 +249,8 @@ void __init setup_arch(char **cmdline_p)
>  		initrd_below_start_ok = 1;
>  	}
>  #endif
> +	/* perform jump_table sorting before paging_init locks down read only memory */
> +	jump_label_init();
>  
>  	/* paging_init() sets up the MMU and marks all pages as reserved */
>  	paging_init();
> -- 
> 2.45.2
> 

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