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

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Message-Id: <f9a7eebe-d36e-4587-b99d-35d4edefdd14@app.fastmail.com>
Date:   Sat, 17 Jun 2023 13:38:29 -0700
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "Mike Rapoport" <rppt@...nel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Cc:     "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>,
        "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 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