linux-kernel - Re: [RFC][PATCH 0/4] Make bpf_jit and kprobes work with CONFIG

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Message-ID: <Zej66vQInnDYgpNy@gmail.com>
Date: Wed, 6 Mar 2024 15:23:22 -0800
From: Calvin Owens <jcalvinowens@...il.com>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: Song Liu <song@...nel.org>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Mike Rapoport <rppt@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Naveen N Rao <naveen.n.rao@...ux.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	David S Miller <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>, bpf@...r.kernel.org,
	linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 0/4] Make bpf_jit and kprobes work with
 CONFIG_MODULES=n

On Wednesday 03/06 at 13:34 -0800, Luis Chamberlain wrote:
> On Wed, Mar 06, 2024 at 12:05:07PM -0800, Calvin Owens wrote:
> > Hello all,
> > 
> > This patchset makes it possible to use bpftrace with kprobes on kernels
> > built without loadable module support.
> 
> This is a step in the right direction for another reason: clearly the
> module_alloc() is not about modules, and we have special reasons for it
> now beyond modules. The effort to share a generalize a huge page for
> these things is also another reason for some of this but that is more
> long term.
> 
> I'm all for minor changes here so to avoid regressions but it seems a
> rename is in order -- if we're going to all this might as well do it
> now. And for that I'd just like to ask you paint the bikeshed with
> Song Liu as he's been the one slowly making way to help us get there
> with the "module: replace module_layout with module_memory",
> and Mike Rapoport as he's had some follow up attempts [0]. As I see it,
> the EXECMEM stuff would be what we use instead then. Mike kept the
> module_alloc() and the execmem was just a wrapper but your move of the
> arch stuff makes sense as well and I think would complement his series
> nicely.

I apologize for missing that. I think these are the four most recent
versions of the different series referenced from that LWN link:

  a) https://lore.kernel.org/all/20230918072955.2507221-1-rppt@kernel.org/
  b) https://lore.kernel.org/all/20230526051529.3387103-1-song@kernel.org/
  c) https://lore.kernel.org/all/20221107223921.3451913-1-song@kernel.org/
  d) https://lore.kernel.org/all/20201120202426.18009-1-rick.p.edgecombe@intel.com/

Song and Mike, please correct me if I'm wrong, but I think what I've
done here (see [1], sorry for not adding you initially) is compatible
with everything both of you have recently proposed above. How do you
feel about this as a first step?

For naming, execmem_alloc() seems reasonable to me? I have no strong
feelings at all, I'll just use that going forward unless somebody else
expresses an opinion.

[1] https://lore.kernel.org/lkml/cover.1709676663.git.jcalvinowens@gmail.com/T/#m337096e158a5f771d0c7c2fb15a3b80a4443226a

> If you're gonna split code up to move to another place, it'd be nice
> if you can add copyright headers as was done with the kernel/module.c
> split into kernel/module/*.c

Silly question: should it be the same copyright header as the original
corresponding module.c, or a new one? I tried to preserve the license
header because I wasn't sure what to do about it.

Thanks,
Calvin

> Can we start with some small basic stuff we can all agree on?
> 
> [0] https://lwn.net/Articles/944857/
> 
>   Luis