Re: [PATCH bpf-next v2] riscv, bpf: Add kfunc support for RV64

[Pu Lehui]

On 2023/2/20 22:34, Björn Töpel wrote:
> Pu Lehui <pulehui@xxxxxxxxxxxxxxx> writes:
>
> > From: Pu Lehui <pulehui@xxxxxxxxxx>
> >
> > As another important missing piece of RV64 JIT, kfunc allow bpf programs
> > call kernel functions. For now, RV64 is sufficient to enable it.
>
> Thanks Lehui!
>
> Maybe we can reword/massage the commit message a bit? What do you think
> about something like:
>
> "Now that the BPF trampoline is supported by RISC-V, it is possible to
> use BPF programs with kfunc calls.

kfunc and bpf trampoline are functionally independent. kfunc [1], like 
bpf helper functions, allows bpf programs to call exported kernel 
functions, while bpf trampoline provides a more efficient way than 
kprobe to act as a mediator between kernel functions and bpf programs, 
and between bpf programs.

In fact, it was already supported before the bpf trampoline 
implementation, I just turned it on. As for RV32 kfunc, it needs to do 
some registers parsing.

[1] https://lore.kernel.org/bpf/20210325015124.1543397-1-kafai@xxxxxx/

> Note that the trampoline functionality is only supported by RV64.
>
> Add bpf_jit_supports_kfunc_call() to the 64-bit JIT."
>
>
> Björn