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

Kent Overstreet
2023-06-16T16:48:16Z

On Fri, Jun 16, 2023 at 11:50:28AM +0300, Mike Rapoport wrote:
> From: "Mike Rapoport (IBM)" <rppt@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().
>
> 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@linux.dev>