From: Masami Hiramatsu <mhiramat@kernel.org>
To: Qi Liu <liuqi115@huawei.com>
Cc: <catalin.marinas@arm.com>, <will@kernel.org>,
<naveen.n.rao@linux.ibm.com>, <anil.s.keshavamurthy@intel.com>,
<davem@davemloft.net>, <linux-arm-kernel@lists.infradead.org>,
<song.bao.hua@hisilicon.com>, <prime.zeng@hisilicon.com>,
<robin.murphy@arm.com>, <f.fangjian@huawei.com>,
<linuxarm@huawei.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] arm64: kprobe: Enable OPTPROBE for arm64
Date: Thu, 5 Aug 2021 10:54:01 +0900 [thread overview]
Message-ID: <20210805105401.4acd3217c566b4e3933f355c@kernel.org> (raw)
In-Reply-To: <20210804060209.95817-1-liuqi115@huawei.com>
On Wed, 4 Aug 2021 14:02:09 +0800
Qi Liu <liuqi115@huawei.com> wrote:
> This patch introduce optprobe for ARM64. In optprobe, probed
> instruction is replaced by a branch instruction to detour
> buffer. Detour buffer contains trampoline code and a call to
> optimized_callback(). optimized_callback() calls opt_pre_handler()
> to execute kprobe handler.
>
> Limitations:
> - We only support !CONFIG_RANDOMIZE_MODULE_REGION_FULL case to
> guarantee the offset between probe point and kprobe pre_handler
> is not larger than 128MiB.
>
> Performance of optprobe on Hip08 platform is test using kprobe
> example module[1] to analyze the latency of a kernel function,
> and here is the result:
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/samples/kprobes/kretprobe_example.c
>
> kprobe before optimized:
> [280709.846380] do_empty returned 0 and took 1530 ns to execute
> [280709.852057] do_empty returned 0 and took 550 ns to execute
> [280709.857631] do_empty returned 0 and took 440 ns to execute
> [280709.863215] do_empty returned 0 and took 380 ns to execute
> [280709.868787] do_empty returned 0 and took 360 ns to execute
> [280709.874362] do_empty returned 0 and took 340 ns to execute
> [280709.879936] do_empty returned 0 and took 320 ns to execute
> [280709.885505] do_empty returned 0 and took 300 ns to execute
> [280709.891075] do_empty returned 0 and took 280 ns to execute
> [280709.896646] do_empty returned 0 and took 290 ns to execute
> [280709.902220] do_empty returned 0 and took 290 ns to execute
> [280709.907807] do_empty returned 0 and took 290 ns to execute
>
> optprobe:
> [ 2965.964572] do_empty returned 0 and took 90 ns to execute
> [ 2965.969952] do_empty returned 0 and took 80 ns to execute
> [ 2965.975332] do_empty returned 0 and took 70 ns to execute
> [ 2965.980714] do_empty returned 0 and took 60 ns to execute
> [ 2965.986128] do_empty returned 0 and took 80 ns to execute
> [ 2965.991507] do_empty returned 0 and took 70 ns to execute
> [ 2965.996884] do_empty returned 0 and took 70 ns to execute
> [ 2966.002262] do_empty returned 0 and took 80 ns to execute
> [ 2966.007642] do_empty returned 0 and took 70 ns to execute
> [ 2966.013020] do_empty returned 0 and took 70 ns to execute
> [ 2966.018400] do_empty returned 0 and took 70 ns to execute
> [ 2966.023779] do_empty returned 0 and took 70 ns to execute
> [ 2966.029158] do_empty returned 0 and took 70 ns to execute
>
> Signed-off-by: Qi Liu <liuqi115@huawei.com>
>
> ---
>
> Changes since V1:
> - Address the comments from Masami, checks for all branch instructions, and
> use aarch64_insn_patch_text_nosync() instead of aarch64_insn_patch_text()
> in each probe.
Is it safe for the multicore system? If it is safe because it modifies
just one instruction (modifying 32bit in atomic), I understand it.
BTW, anyway, you should use _nosync() variant in arch_prepare_optimized_kprobe()
too, beacause the optprobe insn buffer is not touched until the probed instruction
is optimized by br.
[...]
> +int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
> +{
> + kprobe_opcode_t *code;
> + u32 insn;
> + int ret, i;
> + void *addrs[TMPL_END_IDX];
> + void *addr;
> +
> + code = get_optinsn_slot();
> + if (!code)
> + return -ENOMEM;
> +
> + if (!is_offset_in_range((unsigned long)code,
> + (unsigned long)orig->addr + 8))
> + goto error;
> +
> + if (!is_offset_in_range((unsigned long)code + TMPL_CALL_BACK,
> + (unsigned long)optimized_callback))
> + goto error;
> +
> + if (!is_offset_in_range((unsigned long)&code[TMPL_RESTORE_END],
> + (unsigned long)op->kp.addr + 4))
> + goto error;
> +
> + /* Setup template */
> + for (i = 0; i < TMPL_END_IDX; i++)
> + addrs[i] = code + i;
> +
> + ret = aarch64_insn_patch_text(addrs, optprobe_template_entry,
> + TMPL_END_IDX);
You should use aarch64_insn_patch_text_nosync() here (and all the
aarch64_insn_patch_text() in this function too), because the insn
buffer must not executed until the probe point is optimized.
> + if (ret < 0)
> + goto error;
> +
> + /* Set probe information */
> + addr = code + TMPL_VAL_IDX;
> + insn = (unsigned long long)op & 0xffffffff;
> + aarch64_insn_patch_text(&addr, &insn, 1);
> +
> + addr = addr + 4;
> + insn = ((unsigned long long)op & GENMASK_ULL(63, 32)) >> 32;
> + aarch64_insn_patch_text(&addr, &insn, 1);
> +
> + addr = code + TMPL_CALL_BACK;
> + insn = aarch64_insn_gen_branch_imm((unsigned long)addr,
> + (unsigned long)optimized_callback,
> + AARCH64_INSN_BRANCH_LINK);
> + aarch64_insn_patch_text(&addr, &insn, 1);
> +
> + /* The original probed instruction */
> + addr = code + TMPL_RESTORE_ORIGN_INSN;
> + insn = orig->opcode;
> + aarch64_insn_patch_text(&addr, &insn, 1);
> +
> + /* Jump back to next instruction */
> + addr = code + TMPL_RESTORE_END;
> + insn = aarch64_insn_gen_branch_imm(
> + (unsigned long)(&code[TMPL_RESTORE_END]),
> + (unsigned long)(op->kp.addr) + 4,
> + AARCH64_INSN_BRANCH_NOLINK);
> + aarch64_insn_patch_text(&addr, &insn, 1);
> +
> + flush_icache_range((unsigned long)code,
> + (unsigned long)(&code[TMPL_END_IDX]));
> + /* Set op->optinsn.insn means prepared. */
> + op->optinsn.insn = code;
> +
> + return 0;
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2021-08-05 1:54 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-04 6:02 [PATCH v2] arm64: kprobe: Enable OPTPROBE for arm64 Qi Liu
2021-08-05 1:54 ` Masami Hiramatsu [this message]
2021-08-05 9:25 ` liuqi (BA)
2021-08-05 16:44 ` Masami Hiramatsu
2021-08-09 6:33 ` liuqi (BA)
2021-08-05 8:55 ` Song Bao Hua (Barry Song)
2021-08-09 6:44 ` liuqi (BA)
2021-08-09 4:15 ` Amit Kachhap
2021-08-09 7:00 ` liuqi (BA)
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