Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220608000014.3054333-1-jarkko@profian.com> <CAJF2gTQgCn2CyZ4+VBqEEBT2b4+1KxoEXxrd+Ritk=58+U8EFA@mail.gmail.com>
 <YqAy0qjI4Lktk/uJ@iki.fi> <20220608232115.ccd4399f4a1d133e9b65c2a9@kernel.org>
 <CAPhsuW6iUieQvA6KqzSLgtxmjkVSWCuVwNA338DATb_myHxo7w@mail.gmail.com> <f7ff2a8d-4128-dac9-9768-1d98bfb06a06@csgroup.eu>
In-Reply-To: <f7ff2a8d-4128-dac9-9768-1d98bfb06a06@csgroup.eu>
From:   Song Liu <song@kernel.org>
Date:   Thu, 9 Jun 2022 15:23:02 -0700
Message-ID: <CAPhsuW4C0KJT3osBSC9bpi1x7X0HWUE+as+wZi1h63LzHVsptg@mail.gmail.com>
Subject: Re: [PATCH] kprobes: Enable tracing for mololithic kernel images
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Masami Hiramatsu <mhiramat@kernel.org>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Guo Ren <guoren@kernel.org>,
        Jarkko Sakkinen <jarkko@profian.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Nathaniel McCallum <nathaniel@profian.com>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
        Helge Deller <deller@gmx.de>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        "David S. Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Kees Cook <keescook@chromium.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Marco Elver <elver@google.com>,
        Dan Li <ashimida@linux.alibaba.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Chen Zhongjin <chenzhongjin@huawei.com>,
        Nicolas Pitre <nico@fluxnic.net>,
        Mark Brown <broonie@kernel.org>,
        Luis Machado <luis.machado@linaro.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Joey Gouly <joey.gouly@arm.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Atsushi Nemoto <anemo@mba.ocn.ne.jp>,
        Guenter Roeck <linux@roeck-us.net>,
        Dave Anglin <dave.anglin@bell.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Daniel Axtens <dja@axtens.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Jordan Niethe <jniethe5@gmail.com>,
        Anup Patel <anup@brainfault.org>,
        Atish Patra <atishp@atishpatra.org>,
        Changbin Du <changbin.du@intel.com>,
        Heiko Stuebner <heiko@sntech.de>,
        Liao Chang <liaochang1@huawei.com>,
        Philipp Tomsich <philipp.tomsich@vrull.eu>,
        Wu Caize <zepan@sipeed.com>,
        Emil Renner Berthing <kernel@esmil.dk>,
        Alexander Egorenkov <egorenar@linux.ibm.com>,
        Thomas Richter <tmricht@linux.ibm.com>,
        Tobias Huschle <huschle@linux.ibm.com>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Michael Roth <michael.roth@amd.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Javier Martinez Canillas <javierm@redhat.com>,
        Miroslav Benes <mbenes@suse.cz>,
        =?UTF-8?Q?Andr=C3=A9_Almeida?= <andrealmeid@igalia.com>,
        Tiezhu Yang <yangtiezhu@loongson.cn>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Aaron Tomlin <atomlin@redhat.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
        Parisc List <linux-parisc@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        linux-s390 <linux-s390@vger.kernel.org>,
        sparclinux <sparclinux@vger.kernel.org>,
        "linux-modules@vger.kernel.org" <linux-modules@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, Jun 9, 2022 at 1:34 AM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 08/06/2022 =C3=A0 18:12, Song Liu a =C3=A9crit :
> > On Wed, Jun 8, 2022 at 7:21 AM Masami Hiramatsu <mhiramat@kernel.org> w=
rote:
> >>
> >> Hi Jarkko,
> >>
> >> On Wed, 8 Jun 2022 08:25:38 +0300
> >> Jarkko Sakkinen <jarkko@kernel.org> 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 <jarkko@profian.com> =
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 f=
or 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 a=
ll
> >>>>> 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_M=
ODULES
> >>>>> or CONFIG_KPROBES is enabled.  In addition, flag kernel module spec=
ific
> >>>>> 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_all=
oc.
> >>>>
> >>>> 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.sakki=
nen@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 cal=
ling it
> > text_alloc() is not 100% accurate until we change the module code (to u=
se
> > a different API to allocate memory for data).
>
> When CONFIG_ARCH_WANTS_MODULES_DATA_IN_VMALLOC, module code uses
> module_alloc() for text and vmalloc() for data, see function
> move_module() in kernel/module/main.c

Thanks for the pointer! I will play with it.

Song