On Thu, Jun 1, 2023 at 3:13 AM Mike Rapoport [off-list ref] wrote:

From: "Mike Rapoport (IBM)" <rppt@kernel.org>

Hi,

module_alloc() is used everywhere as a mean to allocate memory for code.

Beside being semantically wrong, this unnecessarily ties all subsystmes
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.

This set splits code allocation from modules by introducing
jit_text_alloc(), jit_data_alloc() and jit_free() APIs, replaces call
sites of module_alloc() and module_memfree() with the new APIs and
implements core text and related allocation in a central place.

Instead of architecture specific overrides for module_alloc(), the
architectures that require non-default behaviour for text allocation must
fill jit_alloc_params structure and implement jit_alloc_arch_params() that
returns a pointer to that structure. If an architecture does not implement
jit_alloc_arch_params(), the defaults compatible with the current
modules::module_alloc() are used.

The new jitalloc infrastructure allows decoupling of kprobes and ftrace
from modules, and most importantly it enables ROX allocations for
executable memory.

This set does look cleaner than my version [1]. However, this is
partially because this set only separates text and data; while [1]
also separates rw data, ro data, and ro_after_init data. We need
such separation to fully cover module usage, and to remove
VM_FLUSH_RESET_PERMS. Once we add these logic to this
set, the two versions will look similar.

OTOH, I do like the fact this version enables kprobes (and
potentially ftrace and bpf) without CONFIG_MODULES. And
mm/ seems a better home for the logic.

That being said, besides comments in a few patches, this
version looks good to me. With the fix I suggested for patch
12/13, it passed my tests on x86_64 with modules, kprobes,
ftrace, and BPF.

If we decided to ship this version, I would appreciate it if I
could get more credit for my work in [1] and research work
before that.

Thanks,
Song

[1] https://lore.kernel.org/lkml/20230526051529.3387103-1-song@kernel.org/ (local)