Hi Linus, > On Apr 21, 2022, at 2:28 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Apr 21, 2022 at 12:41 PM Song Liu <song@xxxxxxxxxx> wrote: >> >> The extra logic I had in the original patch was to erase the memory >> when a BPF program is freed. In this case, the memory will be >> returned to the bpf_prog_pack, and stays as RO+X. Actually, I >> am not quite sure whether we need this logic. If not, we only need >> the much simpler version. > > Oh, I think it would be good to do at free time too. > > I just would want that to use the same function we already have for > the allocation-time thing, instead of introducing completely new > infrastructure. That was what looked very odd to me. > > Now, the _smallest_ patch would likely be to just save away that > 'bpf_fill_ill_insns' function pointer in the 'struct bpf_prog_pack' > thing. [...] > > Why not just agree on a name - I suggest 'bpf_jit_fill_hole()' - and > just get rid of that stupid 'bpf_jit_fill_hole_t' type name that only > exists because of this thing? Last night, I had a version which is about 90% same as this idea. However, we cannot really use the same function at free time. The huge page is RO+X at free time, but we are only zeroing out a chunk of it. So regular memset/memcpy won’t work. Instead, we will need something like bpf_arch_text_copy(). Thanks, Song
