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From:   Jianhua Liu <jianhua.ljh@gmail.com>
Date:   Tue, 4 Jan 2022 16:49:29 +0800
Message-ID: <CAAgTQPUL-DPTD2-sPQzYB+Eoko7aw40-bhyE_9Kjd90qowQBfw@mail.gmail.com>
Subject: Re: [PATCH v5] arm64: kprobe: Enable OPTPROBE for arm64
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     "liuqi (BA)" <liuqi115@huawei.com>, Will Deacon <will@kernel.org>,
        Linuxarm <linuxarm@huawei.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
        "Zengtao (B)" <prime.zeng@hisilicon.com>, robin.murphy@arm.com,
        linux-kernel@vger.kernel.org
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On Tue, Jan 4, 2022 at 10:36 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> Hi Jianhua,
>
> On Mon, 3 Jan 2022 17:03:33 +0800
> Jianhua Liu <jianhua.ljh@gmail.com> wrote:
>
> > Hi Qi,
> > I have tested your patch on UNISOC s9863a.
> > Test case "kprobe_example & kretprobe_example" is OK.
> >
> > Two point:
> > 1. backtrace is not perfect.
> >    optprobe_common does not saved frame pointer,
> >    backtrace lacks two calls.
> > such as for dup_mm: lack copy_process-->dup_mm
> > dup_mm backtrace from your patch:
> > [  832.387066] CPU: 0 PID: 296 Comm: sh Not tainted 5.16.0-rc5+ #8
> > [  832.387078] Hardware name: Spreadtrum SP9863A-1H10 Board (DT)
> > [  832.387083] Call trace:
> > [  832.387086]  dump_backtrace+0x0/0x1e0
> > [  832.387103]  show_stack+0x24/0x30
> > [  832.387112]  dump_stack_lvl+0x68/0x84
> > [  832.387123]  dump_stack+0x18/0x34
> > [  832.387131]  handler_pre+0x40/0x50 [kprobe_example]
> > [  832.387143]  opt_pre_handler+0x84/0xc0
> > [  832.387154]  optprobe_optimized_callback+0xec/0x164
> > [  832.387164]  optprobe_common+0x70/0xc4
> > [  832.387173]  kernel_clone+0x98/0x440
> > [  832.387182]  __do_sys_clone+0x54/0x80
> > [  832.387191]  __arm64_sys_clone+0x2c/0x40
> > [  832.387199]  invoke_syscall+0x50/0x120
> > [  832.387208]  el0_svc_common.constprop.0+0x4c/0xf4
> > [  832.387217]  do_el0_svc+0x30/0x9c
> > [  832.387225]  el0_svc+0x20/0x60
> > [  832.387235]  el0t_64_sync_handler+0xe8/0xf0
> > [  832.387242]  el0t_64_sync+0x1a0/0x1a4
> >
> >
> > dup_mm backtrace from other:
> > [  173.352294] CPU: 6 PID: 309 Comm: sh Not tainted 5.16.0-rc5+ #19
> > [  173.352301] Hardware name: Spreadtrum SP9863A-1H10 Board (DT)
> > [  173.352304] Call trace:
> > [  173.352307]  dump_backtrace+0x0/0x1d4
> > [  173.352319]  show_stack+0x18/0x24
> > [  173.352326]  dump_stack_lvl+0x68/0x84
> > [  173.352333]  dump_stack+0x18/0x34
> > [  173.352338]  handler_pre+0x38/0x48 [kprobe_example]
> > [  173.352347]  opt_pre_handler+0x74/0xb0
> > [  173.352354]  optimized_callback+0x108/0x130
> > [  173.352361]  optinsn_slot+0x258/0x1000
> > [  173.352366]  dup_mm+0x4/0x4b0
> > [  173.352373]  copy_process+0x1284/0x1360
> > [  173.352378]  kernel_clone+0x5c/0x3c0
> > [  173.352384]  __do_sys_clone+0x54/0x80
> > [  173.352390]  __arm64_sys_clone+0x24/0x30
> > [  173.352396]  invoke_syscall+0x48/0x114
> > [  173.352402]  el0_svc_common.constprop.0+0x44/0xec
> > [  173.352408]  do_el0_svc+0x24/0x90
> > [  173.352413]  el0_svc+0x20/0x60
> > [  173.352420]  el0t_64_sync_handler+0xe8/0xf0
> > [  173.352427]  el0t_64_sync+0x1a0/0x1a4
>
> Is the second one with your patch?
Yes, the second one is from my patch.

Thanks,
Jianhua

>
> >
> > 2. The reserve memory "OPT_SLOT_SIZE - PAGE_SIZE"  is waste.
> >    kernel/kprobe.c used only one PAGE_SIZE slot memory.
>
> Good catch!
> Qi, can you make an array (or bit map) of usage flags and
> manage the reserved memory?
>
> #define OPT_INSN_PAGES (OPT_SLOT_SIZE/PAGE_SIZE)
> static bool insn_page_in_use[OPT_INSN_PAGES];
>
> void *alloc_optinsn_page(void)
> {
>         int i;
>
>         for (i = 0; i < OPT_INSN_PAGES; i++)
>                 if (!insn_page_in_use[i])
>                         goto found;
>         return NULL;
> found:
>         insn_page_in_use[i] = true;
>         return (void *)((unsigned long)optinsn_slot + PAGE_SIZE * i);
> }
>
> void free_optinsn_page(void *page)
> {
>         unsigned long idx = (unsigned long)page - (unsigned long)optinsn_slot;
>
>         WARN_ONCE(idx & (PAGE_SIZE - 1));
>         idx >>= PAGE_SHIFT;
>         if (WARN_ONCE(idx >= OPT_INSN_PAGES))
>                 return;
>         insn_page_in_use[idx] = false;
> }
>
> Thank you,
>
>
>
>
> --
> Masami Hiramatsu <mhiramat@kernel.org>