netdev - Re: [PATCH v2 02/12] mm: introduce execmem_text_alloc() and jit_text

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Message-ID: <20230619113426.c37bpwvdagbzyevn@moria.home.lan>
Date: Mon, 19 Jun 2023 07:34:26 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Andy Lutomirski <luto@...nel.org>
Cc: Mike Rapoport <rppt@...nel.org>,
	Linux Kernel Mailing List <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>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nadav Amit <nadav.amit@...il.com>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Puranjay Mohan <puranjay12@...il.com>,
	Rick P Edgecombe <rick.p.edgecombe@...el.com>,
	"Russell King (Oracle)" <linux@...linux.org.uk>,
	Song Liu <song@...nel.org>, 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,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH v2 02/12] mm: introduce execmem_text_alloc() and
 jit_text_alloc()

On Sat, Jun 17, 2023 at 01:38:29PM -0700, Andy Lutomirski wrote:
> On Fri, Jun 16, 2023, at 1:50 AM, Mike Rapoport wrote:
> > From: "Mike Rapoport (IBM)" <rppt@...nel.org>
> >
> > module_alloc() is used everywhere as a mean to allocate memory for code.
> >
> > Beside being semantically wrong, this unnecessarily ties all subsystems
> > 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.
> >
> > Start splitting code allocation from modules by introducing
> > execmem_text_alloc(), execmem_free(), jit_text_alloc(), jit_free() APIs.
> >
> > Initially, execmem_text_alloc() and jit_text_alloc() are wrappers for
> > module_alloc() and execmem_free() and jit_free() are replacements of
> > module_memfree() to allow updating all call sites to use the new APIs.
> >
> > The intention semantics for new allocation APIs:
> >
> > * execmem_text_alloc() should be used to allocate memory that must reside
> >   close to the kernel image, like loadable kernel modules and generated
> >   code that is restricted by relative addressing.
> >
> > * jit_text_alloc() should be used to allocate memory for generated code
> >   when there are no restrictions for the code placement. For
> >   architectures that require that any code is within certain distance
> >   from the kernel image, jit_text_alloc() will be essentially aliased to
> >   execmem_text_alloc().
> >
> 
> Is there anything in this series to help users do the appropriate synchronization when the actually populate the allocated memory with code?  See here, for example:
> 
> https://lore.kernel.org/linux-fsdevel/cb6533c6-cea0-4f04-95cf-b8240c6ab405@app.fastmail.com/T/#u

We're still in need of an arch independent text_poke() api.