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

Song Liu
2023-06-16T18:19:00Z

On Fri, Jun 16, 2023 at 9:48 AM Kent Overstreet
<kent.overstreet@linux.dev> wrote:
>
> 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>

Acked-by: Song Liu <song@kernel.org>