From: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> Date: Thu, 23 Jan 2025 21:14:04 -0800 > On Wed, Jan 22, 2025 at 10:38 AM Saket Kumar Bhaskar > <skb99@xxxxxxxxxxxxx> wrote: >> >> For platforms on powerpc architecture with a default page size greater >> than 4096, there was an inconsistency in fragment size calculation. >> This caused the BPF selftest xdp_adjust_tail/xdp_adjust_frags_tail_grow >> to fail on powerpc. >> >> The issue occurred because the fragment buffer size in >> bpf_prog_test_run_xdp() was set to 4096, while the actual data size in >> the fragment within the shared skb was checked against PAGE_SIZE >> (65536 on powerpc) in min_t, causing it to exceed 4096 and be set >> accordingly. This discrepancy led to an overflow when >> bpf_xdp_frags_increase_tail() checked for tailroom, as skb_frag_size(frag) >> could be greater than rxq->frag_size (when PAGE_SIZE > 4096). >> >> This commit updates the page size references to 4096 to ensure consistency >> and prevent overflow issues in fragment size calculations. > > This isn't right. Please fix the selftest instead. It's not _that_ easy, I had tried in the past. Anyway, this patch is *not* a good "solution". If you (Saket) really want to fix this, both test_run and the selftest must be in sync, so you need to (both are arch-dependent): 1) get the correct PAGE_SIZE; 2) calculate the correct tailroom in userspace (which depends on sizeof(shinfo) and SKB_DATA_ALIGN -> SMP_CACHE_BYTES). > > pw-bot: cr Thanks, Olek
