On Sat, Aug 22, 2020 at 12:49 AM Hao Luo <haoluo@xxxxxxxxxx> wrote: > > On Fri, Aug 21, 2020 at 8:31 PM Andrii Nakryiko > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > On Fri, Aug 21, 2020 at 8:26 PM Andrii Nakryiko > > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > > > On Wed, Aug 19, 2020 at 3:42 PM Hao Luo <haoluo@xxxxxxxxxx> wrote: > > > > > > > > Add bpf_per_cpu_ptr() to help bpf programs access percpu vars. > > > > bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the kernel > > > > except that it may return NULL. This happens when the cpu parameter is > > > > out of range. So the caller must check the returned value. > > > > > > > > Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx> > > > > --- > > > > > > The logic looks correct, few naming nits, but otherwise: > > > > > > Acked-by: Andrii Nakryiko <andriin@xxxxxx> > > > > > > > include/linux/bpf.h | 3 ++ > > > > include/linux/btf.h | 11 +++++++ > > > > include/uapi/linux/bpf.h | 14 +++++++++ > > > > kernel/bpf/btf.c | 10 ------- > > > > kernel/bpf/verifier.c | 64 ++++++++++++++++++++++++++++++++++++++-- > > > > kernel/trace/bpf_trace.c | 18 +++++++++++ > > > > 6 files changed, 107 insertions(+), 13 deletions(-) > [...] > > > > btw, having bpf_this_cpu_ptr(const void *ptr) seems worthwhile as well, WDYT? > > > > It's probably not a good idea, IMHO. How does it interact with > preemption? Should we treat it as __this_cpu_ptr()? If so, I feel it's > easy to be misused, if the bpf program is called in a preemptible > context. > > Btw, is bpf programs always called with preemption disabled? How about > interrupts? I haven't thought about these questions before but I think > they matter as we start to have more ways for bpf programs to interact > with the kernel. non-sleepable BPF is always disabling CPU migration, so there is no problem with this_cpu_ptr. For sleepable not sure, but we can disable this helper for sleepable BPF programs, if that's a problem. > > Best, > Hao
