netdev - Re: [PATCH 00/13] mm: jit/text allocator

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Message-ID: <CAPhsuW5Em5Sj9uCGyfM6BheTuvA4pviavRTUK-3MbGsd9yCRbQ@mail.gmail.com>
Date: Thu, 1 Jun 2023 17:36:21 -0700
From: Song Liu <song@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, 
	Catalin Marinas <catalin.marinas@....com>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	"David S. Miller" <davem@...emloft.net>, Dinh Nguyen <dinguyen@...nel.org>, 
	Heiko Carstens <hca@...ux.ibm.com>, Helge Deller <deller@....de>, Huacai Chen <chenhuacai@...nel.org>, 
	Kent Overstreet <kent.overstreet@...ux.dev>, Luis Chamberlain <mcgrof@...nel.org>, 
	Michael Ellerman <mpe@...erman.id.au>, "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Russell King <linux@...linux.org.uk>, 
	Steven Rostedt <rostedt@...dmis.org>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
	Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, bpf@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org, 
	linux-mm@...ck.org, linux-modules@...r.kernel.org, 
	linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev, 
	netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 00/13] mm: jit/text allocator

On Thu, Jun 1, 2023 at 3:13 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> From: "Mike Rapoport (IBM)" <rppt@...nel.org>
>
> Hi,
>
> module_alloc() is used everywhere as a mean to allocate memory for code.
>
> Beside being semantically wrong, this unnecessarily ties all subsystmes
> that need to allocate code, such as ftrace, kprobes and BPF to modules
> and puts the burden of code allocation to the modules code.
>
> Several architectures override module_alloc() because of various
> constraints where the executable memory can be located and this causes
> additional obstacles for improvements of code allocation.
>
> This set splits code allocation from modules by introducing
> jit_text_alloc(), jit_data_alloc() and jit_free() APIs, replaces call
> sites of module_alloc() and module_memfree() with the new APIs and
> implements core text and related allocation in a central place.
>
> Instead of architecture specific overrides for module_alloc(), the
> architectures that require non-default behaviour for text allocation must
> fill jit_alloc_params structure and implement jit_alloc_arch_params() that
> returns a pointer to that structure. If an architecture does not implement
> jit_alloc_arch_params(), the defaults compatible with the current
> modules::module_alloc() are used.
>
> The new jitalloc infrastructure allows decoupling of kprobes and ftrace
> from modules, and most importantly it enables ROX allocations for
> executable memory.

This set does look cleaner than my version [1]. However, this is
partially because this set only separates text and data; while [1]
also separates rw data, ro data, and ro_after_init data. We need
such separation to fully cover module usage, and to remove
VM_FLUSH_RESET_PERMS. Once we add these logic to this
set, the two versions will look similar.

OTOH, I do like the fact this version enables kprobes (and
potentially ftrace and bpf) without CONFIG_MODULES. And
mm/ seems a better home for the logic.

That being said, besides comments in a few patches, this
version looks good to me. With the fix I suggested for patch
12/13, it passed my tests on x86_64 with modules, kprobes,
ftrace, and BPF.

If we decided to ship this version, I would appreciate it if I
could get more credit for my work in [1] and research work
before that.

Thanks,
Song

[1] https://lore.kernel.org/lkml/20230526051529.3387103-1-song@kernel.org/