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

Mike Rapoport
2023-06-18T08:01:19Z

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@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:

This series only factors out the executable allocations from modules and
puts them in a central place.
Anything else would go on top after this lands.

> https://lore.kernel.org/linux-fsdevel/cb6533c6-cea0-4f04-95cf-b8240c6ab405@app.fastmail.com/T/#u

--
Sincerely yours,
Mike.