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Mon, 29 Nov 2021 14:50:23 +0800 Subject: Re: [PATCH v4 2/2] arm64: kprobe: Enable OPTPROBE for arm64 To: Masami Hiramatsu CC: Mark Rutland , , , , , , , , , , , , References: <20210818073336.59678-1-liuqi115@huawei.com> <20210818073336.59678-3-liuqi115@huawei.com> <20210824105001.GA96738@C02TD0UTHF1T.local> <20211127212302.f71345c34e5a62e5e779adb2@kernel.org> <4998f219-eb47-a07c-b3ed-c2ae46a77230@huawei.com> <20211129140040.87c5f423a72c95c90602c2c6@kernel.org> From: "liuqi (BA)" Message-ID: <3f8c1754-b677-971c-2e04-a04678206424@huawei.com> Date: Mon, 29 Nov 2021 14:50:22 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20211129140040.87c5f423a72c95c90602c2c6@kernel.org> Content-Language: en-GB X-Originating-IP: [10.67.102.185] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemm600003.china.huawei.com (7.193.23.202) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211128_225032_412002_2EE01AF7 X-CRM114-Status: GOOD ( 31.53 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2021/11/29 13:00, Masami Hiramatsu wrote: > On Mon, 29 Nov 2021 09:40:30 +0800 > "liuqi (BA)" wrote: > >> >> >> On 2021/11/27 20:23, Masami Hiramatsu wrote: >>> On Fri, 26 Nov 2021 18:31:06 +0800 >>> "liuqi (BA)" wrote: >>> >>>> >>>> >>>> On 2021/8/24 18:50, Mark Rutland wrote: >>>>>> diff --git a/arch/arm64/kernel/probes/optprobe_trampoline.S b/arch/arm64/kernel/probes/optprobe_trampoline.S >>>>>> new file mode 100644 >>>>>> index 000000000000..24d713d400cd >>>>>> --- /dev/null >>>>>> +++ b/arch/arm64/kernel/probes/optprobe_trampoline.S >>>>>> @@ -0,0 +1,37 @@ >>>>>> +/* SPDX-License-Identifier: GPL-2.0 */ >>>>>> +/* >>>>>> + * trampoline entry and return code for optprobes. >>>>>> + */ >>>>>> + >>>>>> +#include >>>>>> +#include >>>>>> +#include >>>>>> + >>>>>> + .global optprobe_template_entry >>>>>> +optprobe_template_entry: >>>>> Please use SYM_*(); see arch/arm64/kernel/entry-ftrace.S for examples of >>>>> how to use that for trampolines. >>>>> >>>>> This should be: >>>>> >>>>> SYM_CODE_START(optprobe_template) >>>>> >>>> Hi all, >>>> >>>> I meet a problem when I use SYM_CODE_START(optprobe_template) to replace >>>> optprobe_template_entry. >>>> >>>> If SYM_CODE_START is used, all optprobe will share one trampoline space. >>>> Under this circumstances, if user register two optprobes, trampoline >>>> will be overwritten by the newer one, and this will cause kernel panic >>>> when the old optprobe is trigger. >>> >>> Hm, this is curious, because the template should be copied to the >>> trampoline buffer for each optprobe and be modified. >>> >>>> >>>> Using optprobe_template_entry will not have this problem, as each >>>> optprobe has its own trampoline space (alloced in get_opinsn_slot()). >>> >>> Yes, it is designed to do so. >>> >>> Thank you, >>> >> >> Hi Masami, >> >> Thanks for your reply. But I also met a problem when using >> get_opinsn_slot() to alloc trampoline buffer. >> >> As module_alloc(like x86) is used to alloc buffer, trampoline is in >> module space, so if origin insn is in kernel space, the range between >> origin insn and trampoline is out of 128M. >> >> As module PLT cannot used here, I have no idea to achieve long jump in >> this situation. Do you have any good idea? > Hi Masami, Thanks so much for your reply. > One possible solution is to use pre-allocated trampoline space in > the text area, as same as ppc64 does. > (See arch/powerpc/kernel/optprobes_head.S, it embeds a space at "optinsn_slot") > I find something interesting in arch/powerpc/kernel/optprobes.c, it use "optinsn_slot" as a public buffer, and use a static "insn_page_in_use" to make sure there is only one optprobe in kernel. If we use this solution , users could only register one optprobe each time. This will also be a limitation for users, what's your opinion about this? > Also, the trampoline can be minimized, since what we need is the > probed address (and the address of struct optprobe). > A single trampoline entry will do the following; > > 1. push lr and a victim register (here, x0) > 2. load the address of optprobe to x0 > 3. call(br) common-optprobe asm code > 4. pop lr and x0 > 5. jump back to (next to) the original place > > Here the common-optprobe asm code does; > > c1. push all registers on the stack (like save_all_base_regs) for making > struct pt_regs. > c2. set the pt_regs address to x1. > c3. call optimized_callback() > c4. return > > Since arm64 will emulate the probed instruction, we can do this. > (On the other hand, x86 needs to run the probed insn in trampoline > code, it will do that between step 4 and 5) > I'll try to minimize the trampoline according to this, Thanks, Qi > The trampoline entry code is just 5 instructions (but may need an > immediate value (&optprobe) needs to be embedded). > > Thank you, > >> >> Thanks, >> Qi >> >>>> >>>> So how to reuse SYM_CODE_START in this situation, does anyone has a >>>> good idea? >>>> >>>> Thanks, >>>> Qi >>>>> ... and note the matching end below. >>>>> >>>>>> + sub sp, sp, #PT_REGS_SIZE >>>>>> + save_all_base_regs >>>>>> + /* Get parameters to optimized_callback() */ >>>>>> + ldr x0, 1f >>>>>> + mov x1, sp >>>>>> + /* Branch to optimized_callback() */ >>>>>> + .global optprobe_template_call >>>>>> +optprobe_template_call: >>>>> SYM_INNER_LABEL(optprobe_template_call, SYM_L_GLOBAL) >>>>> >>>>> ...and likewise for all the other labels. >>>>> >>>>>> + nop >>>>>> + restore_all_base_regs >>>>>> + ldr lr, [sp, #S_LR] >>>>>> + add sp, sp, #PT_REGS_SIZE >>>>>> + .global optprobe_template_restore_orig_insn >>>>>> +optprobe_template_restore_orig_insn: >>>>>> + nop >>>>>> + .global optprobe_template_restore_end >>>>>> +optprobe_template_restore_end: >>>>>> + nop >>>>>> + .global optprobe_template_end >>>>>> +optprobe_template_end: >>>>>> + .global optprobe_template_val >>>>>> +optprobe_template_val: >>>>>> + 1: .long 0 >>>>>> + .long 0 >>>>>> + .global optprobe_template_max_length >>>>>> +optprobe_template_max_length: >>>>> SYM_INNER_LABEL(optprobe_template_end, SYM_L_GLOBAL) >>>>> SYM_CODE_END(optprobe_template) >>>>> >>>>> Thanks, >>>>> Mark. >>>>> >>>>>> -- >>> >>> > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel