Hi Jisheng, On Thu, 22 Aug 2019 11:25:00 +0000 Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> Looks good to me. Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx> 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@xxxxxxxxxx> > + * 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@xxxxxxxxxx>
