Re: [PATCH 1/3] module: Rename module_alloc() to text_alloc() and move to kernel proper

From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	Paul Mackerras <paulus@samba.org>, Zong Li <zong.li@sifive.com>,
	Andi Kleen <ak@linux.intel.com>,
	Paul Burton <paulburton@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Vincent Whitchurch <vincent.whitchurch@axis.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Petr Mladek <pmladek@suse.com>, Brian Gerst <brgerst@gmail.com>,
	Andy Lutomirski <luto@kernel.org>, Yonghong Song <yhs@fb.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Jiri Kosina <jkosina@suse.cz>, Anup Patel <anup.patel@wdc.com>,
	linux-kernel@vger.kernel.org, Philipp Rudo <prudo@linux.ibm.com>,
	Torsten Duwe <duwe@lst.de>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mark Rutland <mark.rutland@arm.com>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	Vincent Chen <deanbo422@gmail.com>,
	"open list:S390" <linux-s390@vger.kernel.org>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Helge Deller <deller@gmx.de>,
	John Fastabend <john.fastabend@gmail.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Iurii Zaikin <yzaikin@google.com>,
	Andrii Nakryiko <andriin@fb.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	"moderated list:ARM PORT" <linux-arm-kernel@lists.infradead.org>,
	Daniel Axtens <dja@axtens.net>,
	Damien Le Moal <damien.lemoal@wdc.com>,
	Peter Oberparleiter <oberpar@linux.ibm.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Atish Patra <atish.patra@wdc.com>, Will Deacon <will@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Nayna Jain <nayna@linux.ibm.com>,
	Ley Foon Tan <ley.foon.tan@intel.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Mao Han <han_mao@c-sky.com>, Marco Elver <elver@google.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Babu Moger <Babu.Moger@amd.com>, Borislav Petkov <bp@alien8.de>,
	Greentime Hu <green.hu@gmail.com>,
	Ben Dooks <ben-linux@fluff.org>, Guan Xuetao <gxt@pku.edu.cn>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	"open list:PARISC ARCHITECTURE" <linux-parisc@vger.kernel.org>,
	Jessica Yu <jeyu@kernel.org>,
	"open list:BPF JIT for MIPS \(32-BIT AND 64-BIT\)"
	<bpf@vger.kernel.org>, "David S. Miller" <davem@davemloft.net>,
	Thiago Jung Bauermann <bauerman@linux.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"open list:SPARC + UltraSPARC \(sparc/sparc64\)"
	<sparclinux@vger.kernel.org>,
	Sandipan Das <sandipan@linux.ibm.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Amit Daniel Kachhap <amit.kachhap@arm.com>,
	Tiezhu Yang <yangtiezhu@loongson.cn>,
	Miroslav Benes <mbenes@suse.cz>, Jiri Olsa <jolsa@redhat.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Anders Roxell <anders.roxell@linaro.org>,
	Sven Schnelle <svens@stackframe.org>,
	"maintainer:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)"
	<x86@kernel.org>,
	"open list:RISC-V ARCHITECTURE" <linux-riscv@lists.infradead.org>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Ingo Molnar <mingo@redhat.com>, Albert Ou <aou@eecs.berkeley.edu>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	KP Singh <kpsingh@chromium.org>,
	Gerald Schaefer <gerald.schaefer@de.ibm.com>,
	Nick Hu <nickhu@andestech.com>,
	"open list:BPF JIT for MIPS \(32-BIT AND 64-BIT\)"
	<netdev@vger.kernel.org>,
	"open list:MIPS" <linux-mips@vger.kernel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	"open list:LINUX FOR POWERPC \(32-BIT AND 64-BIT\)"
	<linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH 1/3] module: Rename module_alloc() to text_alloc() and move to kernel proper
Date: Tue, 14 Jul 2020 14:43:09 +0300	[thread overview]
Message-ID: <20200714114309.GB1463346@linux.intel.com> (raw)
In-Reply-To: <20200714095346.GA1551@shell.armlinux.org.uk>

On Tue, Jul 14, 2020 at 10:53:46AM +0100, Russell King - ARM Linux admin wrote:
> On Tue, Jul 14, 2020 at 12:49:28PM +0300, Jarkko Sakkinen wrote:
> > On Mon, Jul 13, 2020 at 07:34:10PM +0100, Russell King - ARM Linux admin wrote:
> > > On Mon, Jul 13, 2020 at 09:19:37PM +0300, Jarkko Sakkinen wrote:
> > > > Rename module_alloc() to text_alloc() and module_memfree() to
> > > > text_memfree(), and move them to kernel/text.c, which is unconditionally
> > > > compiled to the kernel proper. This allows kprobes, ftrace and bpf to
> > > > allocate space for executable code without requiring to compile the modules
> > > > support (CONFIG_MODULES=y) in.
> > > 
> > > I'm not sure this is a good idea for 32-bit ARM.  The code you are
> > > moving for 32-bit ARM is quite specific to module use in that it also
> > > supports allocating from the vmalloc area, where the module code
> > > knows to add PLT entries.
> > > 
> > > If the other proposed users of this text_alloc() do not have the logic
> > > to add PLT entries when branches between kernel code and this
> > > allocation are not reachable by, e.g. a 26-bit signed offset for 32-bit
> > > ARM code, then this code is not suitable for that use.
> > 
> > My intention is to use this in kprobes code in the place of
> > module_alloc().  I'm not sure why moving this code out of the module
> > subsystem could possibly break anything.  Unfortunately I forgot to add
> > covere letter to my series. Sending v2 with that to explain my use case
> > for this.
> 
> Ah, so you're merely renaming module_alloc() to text_alloc() everywhere?
> It sounded from the initial patch like you were also converting other
> users to use module_alloc().

Yes, exactly. I'm making the allocators unconditionally part of the
kernel proper.

My application for this is test kernels. I never compile anything as
modules when I test a release.

Also, I could imagine that especially in small scale embedded devices,
it could be sometimes useful to be able to have tracing support w/o
module support.

/Jarkko

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv