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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D5C71C43334 for ; Fri, 10 Jun 2022 11:21:55 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4LKJSy31qyz3fnk for ; Fri, 10 Jun 2022 21:21:54 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=DZohO9I/; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=2604:1380:4641:c500::1; helo=dfw.source.kernel.org; envelope-from=ardb@kernel.org; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=DZohO9I/; dkim-atps=neutral Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4LJlD04X5Pz3bmS for ; Thu, 9 Jun 2022 23:23:44 +1000 (AEST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 6698F61D27 for ; Thu, 9 Jun 2022 13:23:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D8D5CC341DA for ; Thu, 9 Jun 2022 13:23:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1654781021; bh=IcMP1Nqp9GJ7GlASLImme5YF3P4SQbrK4SBhBNQ9UV0=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=DZohO9I/XhGeYg2v+fuV+Yw/WbboCcjoukfIhBT2aDkvdb64wTEI+n9fVG2szkT1Y iOL0VKtqEPFb3q+kTZobuUeCKPpQvnexB3/8eJGmQyo1fElI45vcsbeL2sWwWpU1gX ZD6xR0vIOktS3YreT4FGFrduL9pIgfACnV+Gg2Tz9uVBvh8tQgzuzpYWcvEYAY4yMA z1mOoqx6dxmfKuS3GLSypYQ2K2LbKKv4DkruTejbsjqRoldFGtUHoKdl0pfhM9Q4qg OiCa0zfCzNnrBoW80IOu6NyNZhnOl2tvIlWC/jqtdzIlS9C+D3GLFQ8GsJs3aK+uRK 7MUm1zsOnNtFg== Received: by mail-oa1-f41.google.com with SMTP id 586e51a60fabf-fe4ac3b87fso826709fac.3 for ; Thu, 09 Jun 2022 06:23:41 -0700 (PDT) X-Gm-Message-State: AOAM530SyWxPNIszA3ivFjvu331X55Pd9guPsi40gyfSzTY73B3BfP1Y glFnqRsv8aafKsZsfKRVLwjUI0Qw+F3k4d8wvHU= X-Google-Smtp-Source: ABdhPJwc69XiDhgAtEuLcemFuiOzMfwrJQLG3YPNssqJ+a5mUfVOzUfeMKARLXGuY2TVerUlDPEZ6gFkcGbsfRaP3M8= X-Received: by 2002:a05:6808:300e:b0:32c:425e:df34 with SMTP id ay14-20020a056808300e00b0032c425edf34mr1704337oib.126.1654781009990; Thu, 09 Jun 2022 06:23:29 -0700 (PDT) MIME-Version: 1.0 References: <20220608000014.3054333-1-jarkko@profian.com> <20220608232115.ccd4399f4a1d133e9b65c2a9@kernel.org> In-Reply-To: From: Ard Biesheuvel Date: Thu, 9 Jun 2022 15:23:16 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] kprobes: Enable tracing for mololithic kernel images To: Jarkko Sakkinen Content-Type: text/plain; charset="UTF-8" X-Mailman-Approved-At: Fri, 10 Jun 2022 21:09:20 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dan Li , Heiko Stuebner , Linus Walleij , Guo Ren , Alexander Gordeev , Javier Martinez Canillas , Geert Uytterhoeven , Catalin Marinas , Christian Borntraeger , Guenter Roeck , =?UTF-8?Q?Andr=C3=A9_Almeida?= , Michael Roth , Nicholas Piggin , Thomas Gleixner , Andrey Konovalov , Nick Desaulniers , Linux Kernel Mailing List , Luis Chamberlain , Sven Schnelle , Wu Caize , Paul Mackerras , Andrew Morton , Mark Rutland , Luis Machado , Atsushi Nemoto , Dave Hansen , Joey Gouly , "James E.J. Bottomley" , Song Liu , linux-s390 , Ilya Leoshkevich , Anup Patel , Helge Deller , Anil S Keshavamurthy , Masami Hiramatsu , Tom Lendacky , Vasily Gorbik , Philipp Tomsich , Dave Anglin , Linux ARM , Daniel Axtens , Nicolas Pitre , "Eric W. Biederman" , "Aneesh Kumar K.V" , Daniel Bristot de Oliveira , Kefeng Wang , Emil Renner Berthing , Jordan Niethe , Atish Patra , A lexei Starovoitov , Will Deacon , Masahiro Yamada , Jarkko Sakkinen , Sami Tolvanen , "Naveen N. Rao" , Marco Elver , Kees Cook , Steven Rostedt , Nathan Chancellor , "Russell King \(Oracle\)" , Mark Brown , Borislav Petkov , Alexander Egorenkov , Thomas Bogendoerfer , Parisc List , Nathaniel McCallum , Dmitry Torokhov , "David S. Miller" , "Kirill A. Shutemov" , Tobias Huschle , "Peter Zijlstra \(Intel\)" , "H. Peter Anvin" , sparclinux , Tiezhu Yang , Miroslav Benes , Chen Zhongjin , linux-riscv , the arch/x86 maintainers , Russell King , Ingo Molnar , Aaron Tomlin , Albert Ou , Heiko Carstens , Liao Chang , Paul Walmsley , Josh Poimboeuf , Thomas Richter , "open list:BROADCOM NVRAM DRIVER" , Changbin Du , Palmer Dabbelt , linuxppc-dev , linux-modules@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, 9 Jun 2022 at 15:14, Jarkko Sakkinen wrote: > > On Wed, Jun 08, 2022 at 09:12:34AM -0700, Song Liu wrote: > > On Wed, Jun 8, 2022 at 7:21 AM Masami Hiramatsu wrote: > > > > > > Hi Jarkko, > > > > > > On Wed, 8 Jun 2022 08:25:38 +0300 > > > Jarkko Sakkinen wrote: > > > > > > > On Wed, Jun 08, 2022 at 10:35:42AM +0800, Guo Ren wrote: > > > > > . > > > > > > > > > > On Wed, Jun 8, 2022 at 8:02 AM Jarkko Sakkinen wrote: > > > > > > > > > > > > Tracing with kprobes while running a monolithic kernel is currently > > > > > > impossible because CONFIG_KPROBES is dependent of CONFIG_MODULES. This > > > > > > dependency is a result of kprobes code using the module allocator for the > > > > > > trampoline code. > > > > > > > > > > > > Detaching kprobes from modules helps to squeeze down the user space, > > > > > > e.g. when developing new core kernel features, while still having all > > > > > > the nice tracing capabilities. > > > > > > > > > > > > For kernel/ and arch/*, move module_alloc() and module_memfree() to > > > > > > module_alloc.c, and compile as part of vmlinux when either CONFIG_MODULES > > > > > > or CONFIG_KPROBES is enabled. In addition, flag kernel module specific > > > > > > code with CONFIG_MODULES. > > > > > > > > > > > > As the result, kprobes can be used with a monolithic kernel. > > > > > It's strange when MODULES is n, but vmlinux still obtains module_alloc. > > > > > > > > > > Maybe we need a kprobe_alloc, right? > > > > > > > > Perhaps not the best name but at least it documents the fact that > > > > they use the same allocator. > > > > > > > > Few years ago I carved up something "half-way there" for kprobes, > > > > and I used the name text_alloc() [*]. > > > > > > > > [*] https://lore.kernel.org/all/20200724050553.1724168-1-jarkko.sakkinen@linux.intel.com/ > > > > > > Yeah, I remember that. Thank you for updating your patch! > > > I think the idea (split module_alloc() from CONFIG_MODULE) is good to me. > > > If module support maintainers think this name is not good, you may be > > > able to rename it as text_alloc() and make the module_alloc() as a > > > wrapper of it. > > > > IIUC, most users of module_alloc() use it to allocate memory for text, except > > that module code uses it for both text and data. Therefore, I guess calling it > > text_alloc() is not 100% accurate until we change the module code (to use > > a different API to allocate memory for data). > > After reading the feedback, I'd stay on using module_alloc() because > it has arch-specific quirks baked in. Easier to deal with them in one > place. > In that case, please ensure that you enable this only on architectures where it is needed. arm64 implements alloc_insn_page() without relying on module_alloc() so I would not expect to see any changes there.