Re: [PATCH bpf-next v2 0/5] execmem_alloc for BPF programs

[Song Liu <song@kernel.org>]

On Thu, Nov 17, 2022 at 12:50 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> On Mon, Nov 14, 2022 at 12:30:49PM -0800, Song Liu wrote:
> > On Sun, Nov 13, 2022 at 2:35 AM Mike Rapoport <rppt@kernel.org> wrote:
> > >
> > > My concern is that the proposed execmem_alloc() cannot be used for
> > > centralized handling of loading text. I'm not familiar enough with
> > > modules/ftrace/kprobes/BPF to clearly identify the potential caveats, but
> > > my gut feeling is that the proposed execmem_alloc() won't be an improvement
> > > but rather a hindrance for moving to centralized handling of loading text.
> >
> > I don't follow why this could ever be a hindrance. Luis is very excited about
> > this, and I am very sure it works for ftrace, kprobe, and BPF.
>
> Again, it's a gut feeling. But for execmem_alloc() to be a unified place of
> code allocation, it has to work for all architectures. If architectures
> have to override it, then where is the unification?
>
> The implementation you propose if great for x86, but to see it as unified
> solution it should be good at least for the major architectures.

As I mentioned earlier, folks are working on using bpf_prog_pack for BPF
JIT on powerpc. We will also work on something similar for ARM. I guess
these are good enough for major architectures?

>
> > > It feels to me that a lot of ground work is needed to get to the point
> > > where we can use centralized handling of loading text.
> >
> > Could you please be more specific on what is needed?
>
> The most obvious one to implement Peter's suggestion with VM_TOPDOWN_VMAP
> so that execmem_alloc() can be actually used by modules.

Current implementation is an alternative to VM_TOPDOWN_VMAP. I am
very sure it works for modules just like VM_TOPDOWN_VMAP solution.

Thanks,
Song