[PATCH v2 2/2] riscv: Add jump-label implementation

Björn Töpel bjorn.topel at gmail.com
Thu Jul 9 02:23:48 EDT 2020


On Wed, 8 Jul 2020 at 23:10, Emil Renner Berthing <kernel at esmil.dk> wrote:
>
> Add jump-label implementation based on the ARM64 version
> and add CONFIG_JUMP_LABEL=y to the defconfigs.
>
> Signed-off-by: Emil Renner Berthing <kernel at esmil.dk>
> Reviewed-by: Björn Töpel <bjorn.topel at gmail.com>

Tested-by: Björn Töpel <bjorn.topel at gmail.com>

> ---
>
> Tested on the HiFive Unleashed board.
>
> Changes since v1:
> - WARN and give up gracefully if the jump offset cannot be
>   represented in a JAL instruction.
> - Add missing braces.
> - Add CONFIG_JUMP_LABEL=y to defconfigs.
>
> All suggested by Björn Töpel.
>
> Changes since RFC:
> - Use RISCV_PTR and RISCV_LGPTR macros to match struct jump_table
>   also in 32bit kernels.
> - Remove unneeded branch ? 1 : 0, thanks Björn
> - Fix \n\n instead of \n\t mistake
>
>  .../core/jump-labels/arch-support.txt         |  2 +-
>  arch/riscv/Kconfig                            |  2 +
>  arch/riscv/configs/defconfig                  |  1 +
>  arch/riscv/configs/nommu_k210_defconfig       |  1 +
>  arch/riscv/configs/nommu_virt_defconfig       |  1 +
>  arch/riscv/configs/rv32_defconfig             |  1 +
>  arch/riscv/include/asm/jump_label.h           | 59 +++++++++++++++++++
>  arch/riscv/kernel/Makefile                    |  2 +
>  arch/riscv/kernel/jump_label.c                | 49 +++++++++++++++
>  9 files changed, 117 insertions(+), 1 deletion(-)
>  create mode 100644 arch/riscv/include/asm/jump_label.h
>  create mode 100644 arch/riscv/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 632a1c7aefa2..760243d18ed7 100644
> --- a/Documentation/features/core/jump-labels/arch-support.txt
> +++ b/Documentation/features/core/jump-labels/arch-support.txt
> @@ -23,7 +23,7 @@
>      |    openrisc: | TODO |
>      |      parisc: |  ok  |
>      |     powerpc: |  ok  |
> -    |       riscv: | TODO |
> +    |       riscv: |  ok  |
>      |        s390: |  ok  |
>      |          sh: | TODO |
>      |       sparc: |  ok  |
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index fd639937e251..d2f5c53fdc19 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -46,6 +46,8 @@ config RISCV
>         select GENERIC_TIME_VSYSCALL if MMU && 64BIT
>         select HANDLE_DOMAIN_IRQ
>         select HAVE_ARCH_AUDITSYSCALL
> +       select HAVE_ARCH_JUMP_LABEL
> +       select HAVE_ARCH_JUMP_LABEL_RELATIVE
>         select HAVE_ARCH_KASAN if MMU && 64BIT
>         select HAVE_ARCH_KGDB
>         select HAVE_ARCH_KGDB_QXFER_PKT
> diff --git a/arch/riscv/configs/defconfig b/arch/riscv/configs/defconfig
> index 4da4886246a4..d58c93efb603 100644
> --- a/arch/riscv/configs/defconfig
> +++ b/arch/riscv/configs/defconfig
> @@ -17,6 +17,7 @@ CONFIG_BPF_SYSCALL=y
>  CONFIG_SOC_SIFIVE=y
>  CONFIG_SOC_VIRT=y
>  CONFIG_SMP=y
> +CONFIG_JUMP_LABEL=y
>  CONFIG_MODULES=y
>  CONFIG_MODULE_UNLOAD=y
>  CONFIG_NET=y
> diff --git a/arch/riscv/configs/nommu_k210_defconfig b/arch/riscv/configs/nommu_k210_defconfig
> index b48138e329ea..cd1df62b13c7 100644
> --- a/arch/riscv/configs/nommu_k210_defconfig
> +++ b/arch/riscv/configs/nommu_k210_defconfig
> @@ -33,6 +33,7 @@ CONFIG_SMP=y
>  CONFIG_NR_CPUS=2
>  CONFIG_CMDLINE="earlycon console=ttySIF0"
>  CONFIG_CMDLINE_FORCE=y
> +CONFIG_JUMP_LABEL=y
>  # CONFIG_BLOCK is not set
>  CONFIG_BINFMT_FLAT=y
>  # CONFIG_COREDUMP is not set
> diff --git a/arch/riscv/configs/nommu_virt_defconfig b/arch/riscv/configs/nommu_virt_defconfig
> index cf74e179bf90..f27596e9663e 100644
> --- a/arch/riscv/configs/nommu_virt_defconfig
> +++ b/arch/riscv/configs/nommu_virt_defconfig
> @@ -30,6 +30,7 @@ CONFIG_MAXPHYSMEM_2GB=y
>  CONFIG_SMP=y
>  CONFIG_CMDLINE="root=/dev/vda rw earlycon=uart8250,mmio,0x10000000,115200n8 console=ttyS0"
>  CONFIG_CMDLINE_FORCE=y
> +CONFIG_JUMP_LABEL=y
>  # CONFIG_BLK_DEV_BSG is not set
>  CONFIG_PARTITION_ADVANCED=y
>  # CONFIG_MSDOS_PARTITION is not set
> diff --git a/arch/riscv/configs/rv32_defconfig b/arch/riscv/configs/rv32_defconfig
> index 05bbf5240569..3a55f0e00d6c 100644
> --- a/arch/riscv/configs/rv32_defconfig
> +++ b/arch/riscv/configs/rv32_defconfig
> @@ -17,6 +17,7 @@ CONFIG_BPF_SYSCALL=y
>  CONFIG_SOC_VIRT=y
>  CONFIG_ARCH_RV32I=y
>  CONFIG_SMP=y
> +CONFIG_JUMP_LABEL=y
>  CONFIG_MODULES=y
>  CONFIG_MODULE_UNLOAD=y
>  CONFIG_NET=y
> diff --git a/arch/riscv/include/asm/jump_label.h b/arch/riscv/include/asm/jump_label.h
> new file mode 100644
> index 000000000000..d5fb342bfccf
> --- /dev/null
> +++ b/arch/riscv/include/asm/jump_label.h
> @@ -0,0 +1,59 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2020 Emil Renner Berthing
> + *
> + * Based on arch/arm64/include/asm/jump_label.h
> + */
> +#ifndef __ASM_JUMP_LABEL_H
> +#define __ASM_JUMP_LABEL_H
> +
> +#ifndef __ASSEMBLY__
> +
> +#include <linux/types.h>
> +
> +#define JUMP_LABEL_NOP_SIZE 4
> +
> +static __always_inline bool arch_static_branch(struct static_key *key,
> +                                              bool branch)
> +{
> +       asm_volatile_goto(
> +               "       .option push                            \n\t"
> +               "       .option norelax                         \n\t"
> +               "       .option norvc                           \n\t"
> +               "1:     nop                                     \n\t"
> +               "       .option pop                             \n\t"
> +               "       .pushsection    __jump_table, \"aw\"    \n\t"
> +               "       .align          " RISCV_LGPTR "         \n\t"
> +               "       .long           1b - ., %l[label] - .   \n\t"
> +               "       " RISCV_PTR "   %0 - .                  \n\t"
> +               "       .popsection                             \n\t"
> +               :  :  "i"(&((char *)key)[branch]) :  : label);
> +
> +       return false;
> +label:
> +       return true;
> +}
> +
> +static __always_inline bool arch_static_branch_jump(struct static_key *key,
> +                                                   bool branch)
> +{
> +       asm_volatile_goto(
> +               "       .option push                            \n\t"
> +               "       .option norelax                         \n\t"
> +               "       .option norvc                           \n\t"
> +               "1:     jal             zero, %l[label]         \n\t"
> +               "       .option pop                             \n\t"
> +               "       .pushsection    __jump_table, \"aw\"    \n\t"
> +               "       .align          " RISCV_LGPTR "         \n\t"
> +               "       .long           1b - ., %l[label] - .   \n\t"
> +               "       " RISCV_PTR "   %0 - .                  \n\t"
> +               "       .popsection                             \n\t"
> +               :  :  "i"(&((char *)key)[branch]) :  : label);
> +
> +       return false;
> +label:
> +       return true;
> +}
> +
> +#endif  /* __ASSEMBLY__ */
> +#endif /* __ASM_JUMP_LABEL_H */
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index b355cf485671..a5287ab9f7f2 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -53,4 +53,6 @@ endif
>  obj-$(CONFIG_HOTPLUG_CPU)      += cpu-hotplug.o
>  obj-$(CONFIG_KGDB)             += kgdb.o
>
> +obj-$(CONFIG_JUMP_LABEL)       += jump_label.o
> +
>  clean:
> diff --git a/arch/riscv/kernel/jump_label.c b/arch/riscv/kernel/jump_label.c
> new file mode 100644
> index 000000000000..1bab1abc1aa5
> --- /dev/null
> +++ b/arch/riscv/kernel/jump_label.c
> @@ -0,0 +1,49 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2020 Emil Renner Berthing
> + *
> + * Based on arch/arm64/kernel/jump_label.c
> + */
> +#include <linux/kernel.h>
> +#include <linux/jump_label.h>
> +#include <asm/bug.h>
> +#include <asm/patch.h>
> +
> +#define RISCV_INSN_NOP 0x00000013U
> +#define RISCV_INSN_JAL 0x0000006fU
> +
> +void arch_jump_label_transform(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 = jump_entry_target(entry) - jump_entry_code(entry);
> +
> +               if (WARN_ON(offset & 1 || offset < -524288 || offset >= 524288))
> +                       return;
> +
> +               insn = RISCV_INSN_JAL |
> +                       (((u32)offset & GENMASK(19, 12)) << (12 - 12)) |
> +                       (((u32)offset & GENMASK(11, 11)) << (20 - 11)) |
> +                       (((u32)offset & GENMASK(10,  1)) << (21 -  1)) |
> +                       (((u32)offset & GENMASK(20, 20)) << (31 - 20));
> +       } else {
> +               insn = RISCV_INSN_NOP;
> +       }
> +
> +       patch_text_nosync(addr, &insn, sizeof(insn));
> +}
> +
> +void arch_jump_label_transform_static(struct jump_entry *entry,
> +                                     enum jump_label_type type)
> +{
> +       /*
> +        * We use the same instructions in the arch_static_branch and
> +        * arch_static_branch_jump inline functions, so there's no
> +        * need to patch them up here.
> +        * The core will call arch_jump_label_transform  when those
> +        * instructions need to be replaced.
> +        */
> +}
> --
> 2.27.0
>



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