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Subject: Re: [PATCH v2] LoongArch: Add jump-label implementation
To:     WANG Xuerui <kernel@xen0n.name>
References: <1683710206-23905-1-git-send-email-tangyouling@loongson.cn>
 <3b360532-6ad5-b22c-b02a-103be491be4c@xen0n.name>
Cc:     Huacai Chen <chenhuacai@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Jason Baron <jbaron@akamai.com>,
        Zhangjin Wu <falcon@tinylab.org>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, loongarch@lists.linux.dev
From:   Youling Tang <tangyouling@loongson.cn>
Message-ID: <72b6c81a-d4ee-575a-ff48-6be7e034ac96@loongson.cn>
Date:   Thu, 11 May 2023 09:33:37 +0800
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Hi, Xuerui

On 05/10/2023 05:28 PM, WANG Xuerui wrote:
> Hi Youling,
>
> On 2023/5/10 17:16, Youling Tang wrote:
>> Add jump-label implementation based on the ARM64 version.
>
> "Add support for jump labels based on ..." sounds better IMO.

OK.

>
>>
>> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
>> ---
>> Changes in v2:
>> - Fix build errors.
>> - fix comment.
>>
>>   .../core/jump-labels/arch-support.txt         |  2 +-
>>   arch/loongarch/Kconfig                        |  2 +
>>   arch/loongarch/configs/loongson3_defconfig    |  1 +
>>   arch/loongarch/include/asm/jump_label.h       | 51 +++++++++++++++++++
>>   arch/loongarch/kernel/Makefile                |  2 +
>>   arch/loongarch/kernel/jump_label.c            | 23 +++++++++
>>   6 files changed, 80 insertions(+), 1 deletion(-)
>>   create mode 100644 arch/loongarch/include/asm/jump_label.h
>>   create mode 100644 arch/loongarch/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 2328eada3a49..94d9dece580f 100644
>> --- a/Documentation/features/core/jump-labels/arch-support.txt
>> +++ b/Documentation/features/core/jump-labels/arch-support.txt
>> @@ -13,7 +13,7 @@
>>       |        csky: |  ok  |
>>       |     hexagon: | TODO |
>>       |        ia64: | TODO |
>> -    |   loongarch: | TODO |
>> +    |   loongarch: |  ok  |
>
> +1 for updating the docs along with the implementation!
>
>>       |        m68k: | TODO |
>>       |  microblaze: | TODO |
>>       |        mips: |  ok  |
>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>> index d38b066fc931..193a959a5611 100644
>> --- a/arch/loongarch/Kconfig
>> +++ b/arch/loongarch/Kconfig
>> @@ -83,6 +83,8 @@ config LOONGARCH
>>       select GPIOLIB
>>       select HAS_IOPORT
>>       select HAVE_ARCH_AUDITSYSCALL
>> +    select HAVE_ARCH_JUMP_LABEL
>> +    select HAVE_ARCH_JUMP_LABEL_RELATIVE
>>       select HAVE_ARCH_MMAP_RND_BITS if MMU
>>       select HAVE_ARCH_SECCOMP_FILTER
>>       select HAVE_ARCH_TRACEHOOK
>> diff --git a/arch/loongarch/configs/loongson3_defconfig
>> b/arch/loongarch/configs/loongson3_defconfig
>> index 6cd26dd3c134..33a0f5f742f6 100644
>> --- a/arch/loongarch/configs/loongson3_defconfig
>> +++ b/arch/loongarch/configs/loongson3_defconfig
>> @@ -63,6 +63,7 @@ CONFIG_EFI_ZBOOT=y
>>   CONFIG_EFI_GENERIC_STUB_INITRD_CMDLINE_LOADER=y
>>   CONFIG_EFI_CAPSULE_LOADER=m
>>   CONFIG_EFI_TEST=m
>> +CONFIG_JUMP_LABEL=y
>>   CONFIG_MODULES=y
>>   CONFIG_MODULE_FORCE_LOAD=y
>>   CONFIG_MODULE_UNLOAD=y
>> diff --git a/arch/loongarch/include/asm/jump_label.h
>> b/arch/loongarch/include/asm/jump_label.h
>> new file mode 100644
>> index 000000000000..2f9fdec256c5
>> --- /dev/null
>> +++ b/arch/loongarch/include/asm/jump_label.h
>> @@ -0,0 +1,51 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Copyright (C) 2023 Loongson Technology Corporation Limited
>> + *
>> + * 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
>
> Saying LOONGARCH_INSN_SIZE here might be better for reducing redundancy,
> although that'll necessitate an extra include of <asm/inst.h>. Leaving
> the 4 alone won't cause much harm so I'm fine with either.

Using LOONGARCH_INSN_SIZE in v1, but causing build errors due to
inclusion of <asm/inst.h> [1].

So I removed the <asm/inst.h> include and used hardcoded 4.

[1]: 
https://lore.kernel.org/loongarch/202305100412.gazWW71q-lkp@intel.com/T/#m0d8393aaf529aea0a4dcc5985469e698d63d66b3
>
>> +
>> +static __always_inline bool arch_static_branch(struct static_key *
>> const key,
>> +                           const bool branch)
>> +{
>> +    asm_volatile_goto(
>> +        "1:    nop                    \n\t"
>> +         "    .pushsection    __jump_table, \"aw\"    \n\t"
>> +         "    .align        3            \n\t"
>> +         "    .long        1b - ., %l[l_yes] - .    \n\t"
>> +         "    .quad        %0 - .            \n\t"
>> +         "    .popsection                \n\t"
>> +         :  :  "i"(&((char *)key)[branch]) :  : l_yes);
>> +
>> +    return false;
>> +l_yes:
>> +    return true;
>> +}
>> +
>> +static __always_inline bool arch_static_branch_jump(struct static_key
>> * const key,
>> +                            const bool branch)
>> +{
>> +    asm_volatile_goto(
>> +        "1:    b        %l[l_yes]        \n\t"
>> +         "    .pushsection    __jump_table, \"aw\"    \n\t"
>> +         "    .align        3            \n\t"
>> +         "    .long        1b - ., %l[l_yes] - .    \n\t"
>> +         "    .quad        %0 - .            \n\t"
>> +         "    .popsection                \n\t"
>> +         :  :  "i"(&((char *)key)[branch]) :  : l_yes);
>> +
>> +    return false;
>> +l_yes:
>> +    return true;
>> +}
>> +
>> +#endif  /* __ASSEMBLY__ */
>> +#endif    /* __ASM_JUMP_LABEL_H */
>> diff --git a/arch/loongarch/kernel/Makefile
>> b/arch/loongarch/kernel/Makefile
>> index 9a72d91cd104..64ea76f60e2c 100644
>> --- a/arch/loongarch/kernel/Makefile
>> +++ b/arch/loongarch/kernel/Makefile
>> @@ -54,4 +54,6 @@ obj-$(CONFIG_HAVE_HW_BREAKPOINT)    += hw_breakpoint.o
>>     obj-$(CONFIG_KPROBES)        += kprobes.o kprobes_trampoline.o
>>   +obj-$(CONFIG_JUMP_LABEL)    += jump_label.o
>> +
>>   CPPFLAGS_vmlinux.lds        := $(KBUILD_CFLAGS)
>> diff --git a/arch/loongarch/kernel/jump_label.c
>> b/arch/loongarch/kernel/jump_label.c
>> new file mode 100644
>> index 000000000000..b06245955f7a
>> --- /dev/null
>> +++ b/arch/loongarch/kernel/jump_label.c
>> @@ -0,0 +1,23 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Copyright (C) 2023 Loongson Technology Corporation Limited
>> + *
>> + * Based on arch/arm64/kernel/jump_label.c
>> + */
>> +#include <linux/jump_label.h>
>> +#include <linux/kernel.h>
>> +#include <asm/inst.h>
>> +
>> +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)
>
> Please use a switch for dealing with enum-typed values.

Because the current type only has JUMP_LABEL_NOP and JUMP_LABEL_JMP,
using if may be simpler than switch.

Thanks,
Youling.
>
>> +        insn = larch_insn_gen_b(jump_entry_code(entry),
>> jump_entry_target(entry));
>> +    else
>> +        insn = larch_insn_gen_nop();
>> +
>> +    larch_insn_patch_text(addr, insn);
>> +}
>