[PATCH v2 02/12] mm: introduce execmem_text_alloc() and jit_text_alloc()

[Andy Lutomirski]

On Fri, Jun 16, 2023, at 1:50 AM, Mike Rapoport wrote:
> From: "Mike Rapoport (IBM)" <rppt at kernel.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