> On Nov 17, 2021, at 11:54 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Wed, Nov 17, 2021 at 11:57:12PM +0000, Song Liu wrote: > >> I would agree that __text_poke() is a safer option. But in this case, we >> will need the temporary hole to be 2MB in size. Also, we will probably >> hold the temporary mapping for longer time (the whole JITing process). >> Does this sound reasonable? > > No :-) > > Jit to a buffer, then copy the buffer into the 2M page using 4k aliases. > IIRC each program is still smaller than a single page, right? So at no > point do you need more than 2 pages mapped anyway. JITing to a separate buffer adds complexity to the JIT process, as we need to redo some offsets before the copy to match the final location of the program. I don't have much experience with the JIT engine, so I am not very sure how much work it gonna be. The BPF program could have up to 1000000 (BPF_COMPLEXITY_LIMIT_INSNS) instructions (BPF instructions). So it could easily go beyond a few pages. Mapping the 2MB page all together should make the logic simpler. Thanks, Song
