From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9ADCDC433F5 for ; Tue, 30 Nov 2021 06:48:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238809AbhK3Gva (ORCPT ); Tue, 30 Nov 2021 01:51:30 -0500 Received: from szxga01-in.huawei.com ([45.249.212.187]:31927 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238795AbhK3Gv3 (ORCPT ); Tue, 30 Nov 2021 01:51:29 -0500 Received: from dggemv703-chm.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4J3CTZ4vjgzcbkR; Tue, 30 Nov 2021 14:48:02 +0800 (CST) Received: from kwepemm600003.china.huawei.com (7.193.23.202) by dggemv703-chm.china.huawei.com (10.3.19.46) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Tue, 30 Nov 2021 14:48:08 +0800 Received: from [10.67.102.185] (10.67.102.185) by kwepemm600003.china.huawei.com (7.193.23.202) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Tue, 30 Nov 2021 14:48:07 +0800 Subject: Re: [PATCH v4 2/2] arm64: kprobe: Enable OPTPROBE for arm64 To: Masami Hiramatsu , Linuxarm 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> <3f8c1754-b677-971c-2e04-a04678206424@huawei.com> <20211129233514.e59d953a7d90d9f4f3d6a097@kernel.org> From: "liuqi (BA)" Message-ID: <9fdb2ad3-539f-fb4d-7a96-c737fec967f7@huawei.com> Date: Tue, 30 Nov 2021 14:48:06 +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: <20211129233514.e59d953a7d90d9f4f3d6a097@kernel.org> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.102.185] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemm600003.china.huawei.com (7.193.23.202) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/11/29 22:35, Masami Hiramatsu wrote: >>>>>> 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? > No, that is just a memory area for pooling trampoline buffer. So optprobe > can allocate the buffer from that area. Please see kernel/kprobes.c:344. > optprobe allocates "insn_slot" from kprobe_optinsn_slots, which uses > alloc_optinsn_page() to allocate the pool of slots. > > Thank you, > Hi, Thanks for your reply, I test alloc_optinsn_page() and it does work well to alloc the pool of slots. But when I tried to use module PLT, something seems wrong here. Arm64 Module PLT in mod->arch.ftrace_trampolines is set in module_finalize, after that, mod->arch.ftrace_trampolines seems to be a read-only memory. But in arch_optimize_kprobes() we need to modify the destination of PLT (as each optprobe has its own trampoline buffer), if so, we cannot get rid of the 128M branch limit :( Thanks, Qi