On Fri, Jan 6, 2023 at 11:51 AM David Vernet <void@xxxxxxxxxxxxx> wrote: > > BPF kfuncs are kernel functions that can be invoked by BPF programs. > kfuncs can be kernel functions which are also called elsewhere in the > main kernel (such as crash_kexec()), or may be functions that are only > meant to be used by BPF programs, such as bpf_task_acquire(), and which > are not called from anywhere else in the kernel. > > While thus far we haven't observed any issues such as kfuncs being > elided by the compiler, at some point we could easily run into problems > such as the following: > > - static kernel functions that are also used as kfuncs could be inlined > and/or elided by the compiler. > - BPF-specific kfuncs with external linkage may at some point be elided > by the compiler in LTO builds, when it's determined that they aren't > called anywhere. > > To address this, this patch set introduces a new __bpf_kfunc macro which > should be added to all kfuncs, and which will protect kfuncs from such > problems. Note that some kfuncs kind of try to do this already by > specifying noinline or __used. We are inconsistent in how this is > applied. __bpf_kfunc should provide a uniform and more-future-proof way > to do this. The series looks reasonable to me. Would be nice if we can somehow prevent (with a checkpatch?) adding new kfuncs without this new tag, but I don't see an easy way. I was waiting in case other would like to comment, but if nothing to discuss: Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxx> > David Vernet (3): > bpf: Add __bpf_kfunc tag for marking kernel functions as kfuncs > bpf: Document usage of the new __bpf_kfunc macro > bpf: Add __bpf_kfunc tag to all kfuncs > > Documentation/bpf/kfuncs.rst | 18 +++++ > Documentation/conf.py | 3 + > include/linux/btf.h | 9 +++ > kernel/bpf/helpers.c | 19 +++++ > kernel/cgroup/rstat.c | 2 + > kernel/kexec_core.c | 2 + > kernel/trace/bpf_trace.c | 4 + > net/bpf/test_run.c | 76 ++++++++++++------- > net/ipv4/tcp_bbr.c | 8 ++ > net/ipv4/tcp_cong.c | 5 ++ > net/ipv4/tcp_cubic.c | 6 ++ > net/ipv4/tcp_dctcp.c | 6 ++ > net/netfilter/nf_conntrack_bpf.c | 14 +++- > net/netfilter/nf_nat_bpf.c | 1 + > net/xfrm/xfrm_interface_bpf.c | 4 +- > .../selftests/bpf/bpf_testmod/bpf_testmod.c | 2 +- > 16 files changed, 146 insertions(+), 33 deletions(-) > > -- > 2.39.0 >
