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SubjectRe: [PATCH v2 3/3] arm64: implement KPROBES_ON_FTRACE
Date
On Tue, 20 Aug 2019 03:54:20 +0000 Jisheng Zhang 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.
>
> This patch implements KPROBES_ON_FTRACE for arm64.
>
> Tested on berlin arm64 platform.

some performance numbers may be interesting.

HW: Berlin arm64 platform, cpufreq is forced to 800MHZ
SW: getppid syscall micro-benchmark, source code is put at the end of this email.

A. Not probed.
B. Probed at __arm64_sys_getppid w/ non-operation probe functions, w/o KPROBES_ON_FTRACE
C. Probed at __arm64_sys_getppid w/ non-operation probe functions, w/ KPROBES_ON_FTRACE

A: 1905 ns/call
B: 5833 ns/call
C: 2169 ns/call

The overhead of kprobes is 5833 - 1905 = 3928 ns/call
The overhead of kprobes w/ KPROBES_ON_FTRACE is 2169 - 1905 = 264 ns/call

As can be seen, KPROBES_ON_FTRACE significantly reduce the overhead of kprobes.

Thanks

<---8---
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <unistd.h>

int main (int argc, char *argv[])
{
struct timeval tv;
unsigned long count;
struct rusage usage;

for (count = 0; count < 10000000; count++)
getppid();
getrusage(RUSAGE_SELF, &usage);
tv = usage.ru_stime;
tv.tv_sec += usage.ru_utime.tv_sec;
tv.tv_usec += usage.ru_utime.tv_usec;
fprintf(stderr, "getppid was called %u times: %d nsec per call\n",
count, (tv.tv_sec*1000*1000 + tv.tv_usec)/(count/1000));

return 0;
}

>
> ~ # 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@synaptics.com>
> ---
> .../debug/kprobes-on-ftrace/arch-support.txt | 2 +-
> arch/arm64/Kconfig | 1 +
> arch/arm64/kernel/probes/Makefile | 1 +
> arch/arm64/kernel/probes/ftrace.c | 60 +++++++++++++++++++
> 4 files changed, 63 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..52901ffff570
> --- /dev/null
> +++ b/arch/arm64/kernel/probes/ftrace.c
> @@ -0,0 +1,60 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Dynamic Ftrace based Kprobes Optimization
> + *
> + * Copyright (C) Hitachi Ltd., 2012
> + * Copyright (C) 2019 Jisheng Zhang <jszhang@kernel.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);
> + /* Kprobe handler expects regs->pc = pc + 1 as breakpoint hit */
> + instruction_pointer_set(regs, ip + sizeof(kprobe_opcode_t));
> +
> + __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);
> +
> +int arch_prepare_kprobe_ftrace(struct kprobe *p)
> +{
> + p->ainsn.api.insn = NULL;
> + return 0;
> +}
> --
> 2.23.0.rc1
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org

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