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Message-ID: <20131030005558.GE25346@mudshark.cambridge.arm.com>
Date: Wed, 30 Oct 2013 00:55:58 +0000
From: Will Deacon <will.deacon@....com>
To: Jiang Liu <liuj97@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Catalin Marinas <Catalin.Marinas@....com>,
Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
Jiang Liu <jiang.liu@...wei.com>,
Marc Zyngier <Marc.Zyngier@....com>,
Arnd Bergmann <arnd@...db.de>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 6/7] arm64, jump label: optimize jump label
implementation
On Fri, Oct 18, 2013 at 04:20:00PM +0100, Jiang Liu wrote:
> From: Jiang Liu <jiang.liu@...wei.com>
>
> Optimize jump label implementation for ARM64 by dynamically patching
> kernel text.
>
> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
> Cc: Jiang Liu <liuj97@...il.com>
> ---
> arch/arm64/Kconfig | 1 +
> arch/arm64/include/asm/jump_label.h | 52 +++++++++++++++++++++++++++++++++
> arch/arm64/kernel/Makefile | 1 +
> arch/arm64/kernel/jump_label.c | 58 +++++++++++++++++++++++++++++++++++++
> 4 files changed, 112 insertions(+)
> create mode 100644 arch/arm64/include/asm/jump_label.h
> create mode 100644 arch/arm64/kernel/jump_label.c
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index c044548..da388e4 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -17,6 +17,7 @@ config ARM64
> select GENERIC_SMP_IDLE_THREAD
> select GENERIC_TIME_VSYSCALL
> select HARDIRQS_SW_RESEND
> + select HAVE_ARCH_JUMP_LABEL
> select HAVE_ARCH_TRACEHOOK
> select HAVE_DEBUG_BUGVERBOSE
> select HAVE_DEBUG_KMEMLEAK
> diff --git a/arch/arm64/include/asm/jump_label.h b/arch/arm64/include/asm/jump_label.h
> new file mode 100644
> index 0000000..d268fab
> --- /dev/null
> +++ b/arch/arm64/include/asm/jump_label.h
> @@ -0,0 +1,52 @@
> +/*
> + * Copyright (C) 2013 Huawei Ltd.
> + * Author: Jiang Liu <jiang.liu@...wei.com>
> + *
> + * Based on arch/arm/include/asm/jump_label.h
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program. If not, see <http://www.gnu.org/licenses/>.
> + */
> +#ifndef _ASM_ARM64_JUMP_LABEL_H
> +#define _ASM_ARM64_JUMP_LABEL_H
> +#include <linux/types.h>
> +
> +#ifdef __KERNEL__
> +
> +#define JUMP_LABEL_NOP_SIZE 4
> +
> +static __always_inline bool arch_static_branch(struct static_key *key)
> +{
> + asm goto("1:\n\t"
> + "nop\n\t"
Minor nit: can you put the label on the same line as the nop please?
> + ".pushsection __jump_table, \"aw\"\n\t"
> + ".align 3\n\t"
> + ".quad 1b, %l[l_yes], %c0\n\t"
> + ".popsection\n\t"
> + : : "i"(key) : : l_yes);
> +
> + return false;
> +l_yes:
> + return true;
> +}
> +
> +#endif /* __KERNEL__ */
> +
> +typedef u64 jump_label_t;
> +
> +struct jump_entry {
> + jump_label_t code;
> + jump_label_t target;
> + jump_label_t key;
> +};
> +
> +#endif /* _ASM_ARM64_JUMP_LABEL_H */
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 9af6cb3..b7db65e 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -18,6 +18,7 @@ arm64-obj-$(CONFIG_SMP) += smp.o smp_spin_table.o smp_psci.o
> arm64-obj-$(CONFIG_HW_PERF_EVENTS) += perf_event.o
> arm64-obj-$(CONFIG_HAVE_HW_BREAKPOINT)+= hw_breakpoint.o
> arm64-obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
> +arm64-obj-$(CONFIG_JUMP_LABEL) += jump_label.o
>
> obj-y += $(arm64-obj-y) vdso/
> obj-m += $(arm64-obj-m)
> diff --git a/arch/arm64/kernel/jump_label.c b/arch/arm64/kernel/jump_label.c
> new file mode 100644
> index 0000000..871786a
> --- /dev/null
> +++ b/arch/arm64/kernel/jump_label.c
> @@ -0,0 +1,58 @@
> +/*
> + * Copyright (C) 2013 Huawei Ltd.
> + * Author: Jiang Liu <jiang.liu@...wei.com>
> + *
> + * Based on arch/arm/kernel/jump_label.c
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program. If not, see <http://www.gnu.org/licenses/>.
> + */
> +#include <linux/kernel.h>
> +#include <linux/jump_label.h>
> +#include <asm/jump_label.h>
> +#include <asm/insn.h>
> +
> +#ifdef HAVE_JUMP_LABEL
> +
> +static void __arch_jump_label_transform(struct jump_entry *entry,
> + enum jump_label_type type,
> + bool is_static)
> +{
> + void *addr = (void *)entry->code;
> + u32 insn;
> +
> + if (type == JUMP_LABEL_ENABLE) {
> + insn = aarch64_insn_gen_branch_imm(entry->code,
> + entry->target, 0);
Maybe have an enum or #define for the last parameter -- it's not at all
obvious that '0' means `no link'.
> + } else {
> + insn = aarch64_insn_gen_nop();
> + }
> +
> + if (is_static)
> + aarch64_insn_patch_text_nosync(&addr, &insn, 1);
I think I mentioned this before, but is it ever safe to patch more than one
instruction in the _nosync case? If not, I wouldn't even bother with that
last argument.
Will
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