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Message-Id: <20190823235721.fa481fca3475a3afd92c740c@kernel.org>
Date: Fri, 23 Aug 2019 23:57:21 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
Jonathan Corbet <corbet@....net>,
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Mark Rutland <mark.rutland@....com>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
Will Deacon <will@...nel.org>
Subject: Re: [PATCH v5] arm64: implement KPROBES_ON_FTRACE
Hi Jisheng,
On Thu, 22 Aug 2019 11:25:00 +0000
Jisheng Zhang <Jisheng.Zhang@...aptics.com> wrote:
> KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it
> eliminates the need for a trap, as well as the need to emulate or
> single-step instructions.
>
> Tested on berlin arm64 platform.
>
> ~ # mount -t debugfs debugfs /sys/kernel/debug/
> ~ # cd /sys/kernel/debug/
> /sys/kernel/debug # echo 'p _do_fork' > tracing/kprobe_events
>
> before the patch:
>
> /sys/kernel/debug # cat kprobes/list
> ffffff801009fe28 k _do_fork+0x0 [DISABLED]
>
> after the patch:
>
> /sys/kernel/debug # cat kprobes/list
> ffffff801009ff54 k _do_fork+0x4 [DISABLED][FTRACE]
>
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Looks good to me.
Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
Thank you,
> ---
>
> KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it
> eliminates the need for a trap, as well as the need to emulate or
> single-step instructions.
>
> Applied after arm64 FTRACE_WITH_REGS:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2019-August/674404.html
>
> Changes since v4:
> - correct reg->pc: probed on foo, then pre_handler see foo+0x4, while
> post_handler see foo+0x8
>
> Changes since v3:
> - move kprobe_lookup_name() and arch_kprobe_on_func_entry to ftrace.c since
> we only want to choose the ftrace entry for KPROBES_ON_FTRACE.
> - only choose ftrace entry if (addr && !offset)
>
> Changes since v2:
> - remove patch1, make it a single cleanup patch
> - remove "This patch" in the change log
> - implement arm64's kprobe_lookup_name() and arch_kprobe_on_func_entry instead
> of patching the common kprobes code
>
> Changes since v1:
> - make the kprobes/x86: use instruction_pointer and instruction_pointer_set
> as patch1
> - add Masami's ACK to patch1
> - add some description about KPROBES_ON_FTRACE and why we need it on
> arm64
> - correct the log before the patch
> - remove the consolidation patch, make it as TODO
> - only adjust kprobe's addr when KPROBE_FLAG_FTRACE is set
> - if KPROBES_ON_FTRACE, ftrace_call_adjust() the kprobe's addr before
> calling ftrace_location()
> - update the kprobes-on-ftrace/arch-support.txt in doc
>
> .../debug/kprobes-on-ftrace/arch-support.txt | 2 +-
> arch/arm64/Kconfig | 1 +
> arch/arm64/kernel/probes/Makefile | 1 +
> arch/arm64/kernel/probes/ftrace.c | 83 +++++++++++++++++++
> 4 files changed, 86 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/kernel/probes/ftrace.c
>
> diff --git a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt
> index 68f266944d5f..e8358a38981c 100644
> --- a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt
> +++ b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt
> @@ -9,7 +9,7 @@
> | alpha: | TODO |
> | arc: | TODO |
> | arm: | TODO |
> - | arm64: | TODO |
> + | arm64: | ok |
> | c6x: | TODO |
> | csky: | TODO |
> | h8300: | TODO |
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 663392d1eae2..928700f15e23 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -167,6 +167,7 @@ config ARM64
> select HAVE_STACKPROTECTOR
> select HAVE_SYSCALL_TRACEPOINTS
> select HAVE_KPROBES
> + select HAVE_KPROBES_ON_FTRACE
> select HAVE_KRETPROBES
> select HAVE_GENERIC_VDSO
> select IOMMU_DMA if IOMMU_SUPPORT
> diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile
> index 8e4be92e25b1..4020cfc66564 100644
> --- a/arch/arm64/kernel/probes/Makefile
> +++ b/arch/arm64/kernel/probes/Makefile
> @@ -4,3 +4,4 @@ obj-$(CONFIG_KPROBES) += kprobes.o decode-insn.o \
> simulate-insn.o
> obj-$(CONFIG_UPROBES) += uprobes.o decode-insn.o \
> simulate-insn.o
> +obj-$(CONFIG_KPROBES_ON_FTRACE) += ftrace.o
> diff --git a/arch/arm64/kernel/probes/ftrace.c b/arch/arm64/kernel/probes/ftrace.c
> new file mode 100644
> index 000000000000..9f80905f02fa
> --- /dev/null
> +++ b/arch/arm64/kernel/probes/ftrace.c
> @@ -0,0 +1,83 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Dynamic Ftrace based Kprobes Optimization
> + *
> + * Copyright (C) Hitachi Ltd., 2012
> + * Copyright (C) 2019 Jisheng Zhang <jszhang@...nel.org>
> + * Synaptics Incorporated
> + */
> +
> +#include <linux/kprobes.h>
> +
> +/* Ftrace callback handler for kprobes -- called under preepmt disabed */
> +void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
> + struct ftrace_ops *ops, struct pt_regs *regs)
> +{
> + struct kprobe *p;
> + struct kprobe_ctlblk *kcb;
> +
> + /* Preempt is disabled by ftrace */
> + p = get_kprobe((kprobe_opcode_t *)ip);
> + if (unlikely(!p) || kprobe_disabled(p))
> + return;
> +
> + kcb = get_kprobe_ctlblk();
> + if (kprobe_running()) {
> + kprobes_inc_nmissed_count(p);
> + } else {
> + unsigned long orig_ip = instruction_pointer(regs);
> +
> + instruction_pointer_set(regs, ip);
> + __this_cpu_write(current_kprobe, p);
> + kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> + if (!p->pre_handler || !p->pre_handler(p, regs)) {
> + /*
> + * Emulate singlestep (and also recover regs->pc)
> + * as if there is a nop
> + */
> + instruction_pointer_set(regs,
> + (unsigned long)p->addr + MCOUNT_INSN_SIZE);
> + if (unlikely(p->post_handler)) {
> + kcb->kprobe_status = KPROBE_HIT_SSDONE;
> + p->post_handler(p, regs, 0);
> + }
> + instruction_pointer_set(regs, orig_ip);
> + }
> + /*
> + * If pre_handler returns !0, it changes regs->pc. We have to
> + * skip emulating post_handler.
> + */
> + __this_cpu_write(current_kprobe, NULL);
> + }
> +}
> +NOKPROBE_SYMBOL(kprobe_ftrace_handler);
> +
> +kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
> +{
> + unsigned long addr = kallsyms_lookup_name(name);
> +
> + if (addr && !offset) {
> + unsigned long faddr;
> + /*
> + * with -fpatchable-function-entry=2, the first 4 bytes is the
> + * LR saver, then the actual call insn. So ftrace location is
> + * always on the first 4 bytes offset.
> + */
> + faddr = ftrace_location_range(addr,
> + addr + AARCH64_INSN_SIZE);
> + if (faddr)
> + return (kprobe_opcode_t *)faddr;
> + }
> + return (kprobe_opcode_t *)addr;
> +}
> +
> +bool arch_kprobe_on_func_entry(unsigned long offset)
> +{
> + return offset <= AARCH64_INSN_SIZE;
> +}
> +
> +int arch_prepare_kprobe_ftrace(struct kprobe *p)
> +{
> + p->ainsn.api.insn = NULL;
> + return 0;
> +}
> --
> 2.23.0.rc1
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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