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

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Date: Fri, 16 Jun 2023 12:48:02 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
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>,
	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 Edgecombe <rick.p.edgecombe@...el.com>,
	Russell King <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, x86@...nel.org
Subject: Re: [PATCH v2 02/12] mm: introduce execmem_text_alloc() and
 jit_text_alloc()

On Fri, Jun 16, 2023 at 11:50:28AM +0300, 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().
> 
> The names execmem_text_alloc() and jit_text_alloc() emphasize that the
> allocated memory is for executable code, the allocations of the
> associated data, like data sections of a module will use
> execmem_data_alloc() interface that will be added later.

I like the API split - at the risk of further bikeshedding, perhaps
near_text_alloc() and far_text_alloc()? Would be more explicit.

Reviewed-by: Kent Overstreet <kent.overstreet@...ux.dev>