Re: [PATCH bpf-next v1 0/4] Support bpf trampoline for RV64

[Björn Töpel]

Pu Lehui <pulehui@xxxxxxxxxxxxxxx> writes:

> BPF trampoline is the critical infrastructure of the bpf
> subsystem, acting as a mediator between kernel functions
> and BPF programs. Numerous important features, such as
> using ebpf program for zero overhead kernel introspection,
> rely on this key component. We can't wait to support bpf
> trampoline on RV64. Since RV64 does not support ftrace
> direct call yet, the current RV64 bpf trampoline is only
> used in bpf context.
>
> As most of riscv cpu support unaligned memory accesses,
> we temporarily use patch [1] to facilitate testing. The
> test results are as follow, and test_verifier with no
> new failure ceses.
>
> - fexit_bpf2bpf:OK
> - dummy_st_ops:OK
> - xdp_bpf2bpf:OK
>
> [1] https://lore.kernel.org/linux-riscv/20210916130855.4054926-2-chenhuang5@xxxxxxxxxx/
>
> v1:
> - Remove the logic of bpf_arch_text_poke supported for
>   kernel functions. (Kuohai and Björn)
> - Extend patch_text for multiple instructions. (Björn)
> - Fix OOB issue when image too big. (Björn)

This series is ready to go in as is.

@Palmer I'd like to take this series via the bpf-next tree (as usual),
but note that there are some non-BPF changes as well, related to text
poking.

@Lehui I'd like to see two follow-up patches:

1. Enable kfunc for RV64, by adding:
 | bool bpf_jit_supports_kfunc_call(void)
 | {
 |         return true;
 | }

2. Remove the checkpatch warning on patch 4:
 | WARNING: kfree(NULL) is safe and this check is probably not required
 | #313: FILE: arch/riscv/net/bpf_jit_comp64.c:984:
 | +	if (branches_off)
 | +		kfree(branches_off);


For the series:

Tested-by: Björn Töpel <bjorn@xxxxxxxxxxxx>
Acked-by: Björn Töpel <bjorn@xxxxxxxxxxxx>