From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BC25C433F5 for ; Wed, 23 Feb 2022 21:41:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241960AbiBWVmE (ORCPT ); Wed, 23 Feb 2022 16:42:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234362AbiBWVmE (ORCPT ); Wed, 23 Feb 2022 16:42:04 -0500 Received: from mail-pg1-x52b.google.com (mail-pg1-x52b.google.com [IPv6:2607:f8b0:4864:20::52b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A074913D77; Wed, 23 Feb 2022 13:41:34 -0800 (PST) Received: by mail-pg1-x52b.google.com with SMTP id o8so2552023pgf.9; Wed, 23 Feb 2022 13:41:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=EG+iB3dFwWjygwETyeLB9Os/1lUyeWVlILzRoMGRiFE=; b=jUTL1UK7tCThWjlmG8kcatM4NJsuIbOhe+O/CWvbejFwB9eyuk6oUgrQNU+IfMBAvj Jn6o//EtdGiBnmMFTZ8ZToAmm6+p2nQpAsLMpeSiR9WHwYxTQpdvpYHCzSTcUom/uniH E5HSrFxhgkWYdfeqVM+30IeiY/ARWDfckEv+HuBnx+3kjGh4ocHnPaR3CkqBpWPsxVhh SV63hRgTZKRTci4nT7rMAbzW5XcLKZzFNjusmo7RkHOVljd+lXCwNHuOK9mJDWfeLWpY XnJ+rDpsKXwX4aqOPOlg0YN8IBdP0izQCTWSwtLnfGiMDWmAmY0hENRNbBXyAvYR8j+V iDkA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=EG+iB3dFwWjygwETyeLB9Os/1lUyeWVlILzRoMGRiFE=; b=24jZjUdVrbOFJElgkQFPvMfIYrWU5FdGFlfQmZ2AbCBK8gT04vpuDSlkJ0aUqpy/sX QgFBe+OIPKBNdr+nrAA8tb9sOq+aaQ5SHy4g7r/FgByXSfMV5Y/qHq86uPgzDgCrthR3 bRaW7dwfxRf6efAWK5GSUrMua2cz59+oD3+VXXMJYfTqIkTvjhERSfdtiy9LgkUKKNln 0Z8FObYMqzrjifLQuMbLyEozu3xWIUzhoshP4AiCYfKJgpbwqYC5uikgYUJ5T0+9mgGm xusf7lJ0RDQMGUuxdILY0bj8hiexmH03ERux2ixNUKZ6dvl5O225mLUDOx4qb+eC3ub5 jExA== X-Gm-Message-State: AOAM532Bhk1DKaFp6vCbGyNdq0PxZGqclxJG8sCJNk/C2hEQDSOOHkrI dY/rJZHkp1ETkJ3t04tNKRyQEEjw6ytqgp0Jw7kUIBycOko= X-Google-Smtp-Source: ABdhPJwlZWzWiS/QIXthR8l+4QB/0GvALzT7M+6p+lqZhRcg1BQGGGOBSq4XVmwGku9vPHG1gY/gSHGJlip4bX5Q7qA= X-Received: by 2002:a63:602:0:b0:373:efe4:8a24 with SMTP id 2-20020a630602000000b00373efe48a24mr1221110pgg.287.1645652493978; Wed, 23 Feb 2022 13:41:33 -0800 (PST) MIME-Version: 1.0 References: <20220220134813.3411982-1-memxor@gmail.com> <20220220134813.3411982-9-memxor@gmail.com> <20220222070405.i6esgcf7ouqrmoef@ast-mbp.dhcp.thefacebook.com> <20220223031310.d2jh4uwffn3jzoy4@apollo.legion> In-Reply-To: <20220223031310.d2jh4uwffn3jzoy4@apollo.legion> From: Alexei Starovoitov Date: Wed, 23 Feb 2022 13:41:22 -0800 Message-ID: Subject: Re: [PATCH bpf-next v1 08/15] bpf: Adapt copy_map_value for multiple offset case To: Kumar Kartikeya Dwivedi Cc: bpf , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= , Jesper Dangaard Brouer , netfilter-devel , Network Development Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Tue, Feb 22, 2022 at 7:13 PM Kumar Kartikeya Dwivedi wrote: > > On Tue, Feb 22, 2022 at 12:34:05PM IST, Alexei Starovoitov wrote: > > On Sun, Feb 20, 2022 at 07:18:06PM +0530, Kumar Kartikeya Dwivedi wrote: > > > The changes in this patch deserve closer look, so it has been split into > > > its own independent patch. While earlier we just had to skip two objects > > > at most while copying in and out of map, now we have potentially many > > > objects (at most 8 + 2 = 10, due to the BPF_MAP_VALUE_OFF_MAX limit). > > > > > > Hence, divide the copy_map_value function into an inlined fast path and > > > function call to slowpath. The slowpath handles the case of > 3 offsets, > > > while we handle the most common cases (0, 1, 2, or 3 offsets) in the > > > inline function itself. > > > > > > In copy_map_value_slow, we use 11 offsets, just to make the for loop > > > that copies the value free of edge cases for the last offset, by using > > > map->value_size as final offset to subtract remaining area to copy from. > > > > > > Signed-off-by: Kumar Kartikeya Dwivedi > > > --- > > > include/linux/bpf.h | 43 +++++++++++++++++++++++++++++++--- > > > kernel/bpf/syscall.c | 55 ++++++++++++++++++++++++++++++++++++++++++++ > > > 2 files changed, 95 insertions(+), 3 deletions(-) > > > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > > index ae599aaf8d4c..5d845ca02eba 100644 > > > --- a/include/linux/bpf.h > > > +++ b/include/linux/bpf.h > > > @@ -253,12 +253,22 @@ static inline void check_and_init_map_value(struct bpf_map *map, void *dst) > > > memset(dst + map->spin_lock_off, 0, sizeof(struct bpf_spin_lock)); > > > if (unlikely(map_value_has_timer(map))) > > > memset(dst + map->timer_off, 0, sizeof(struct bpf_timer)); > > > + if (unlikely(map_value_has_ptr_to_btf_id(map))) { > > > + struct bpf_map_value_off *tab = map->ptr_off_tab; > > > + int i; > > > + > > > + for (i = 0; i < tab->nr_off; i++) > > > + *(u64 *)(dst + tab->off[i].offset) = 0; > > > + } > > > } > > > > > > +void copy_map_value_slow(struct bpf_map *map, void *dst, void *src, u32 s_off, > > > + u32 s_sz, u32 t_off, u32 t_sz); > > > + > > > /* copy everything but bpf_spin_lock and bpf_timer. There could be one of each. */ > > > static inline void copy_map_value(struct bpf_map *map, void *dst, void *src) > > > { > > > - u32 s_off = 0, s_sz = 0, t_off = 0, t_sz = 0; > > > + u32 s_off = 0, s_sz = 0, t_off = 0, t_sz = 0, p_off = 0, p_sz = 0; > > > > > > if (unlikely(map_value_has_spin_lock(map))) { > > > s_off = map->spin_lock_off; > > > @@ -268,13 +278,40 @@ static inline void copy_map_value(struct bpf_map *map, void *dst, void *src) > > > t_off = map->timer_off; > > > t_sz = sizeof(struct bpf_timer); > > > } > > > + /* Multiple offset case is slow, offload to function */ > > > + if (unlikely(map_value_has_ptr_to_btf_id(map))) { > > > + struct bpf_map_value_off *tab = map->ptr_off_tab; > > > + > > > + /* Inline the likely common case */ > > > + if (likely(tab->nr_off == 1)) { > > > + p_off = tab->off[0].offset; > > > + p_sz = sizeof(u64); > > > + } else { > > > + copy_map_value_slow(map, dst, src, s_off, s_sz, t_off, t_sz); > > > + return; > > > + } > > > + } > > > + > > > + if (unlikely(s_sz || t_sz || p_sz)) { > > > + /* The order is p_off, t_off, s_off, use insertion sort */ > > > > > > - if (unlikely(s_sz || t_sz)) { > > > + if (t_off < p_off || !t_sz) { > > > + swap(t_off, p_off); > > > + swap(t_sz, p_sz); > > > + } > > > if (s_off < t_off || !s_sz) { > > > swap(s_off, t_off); > > > swap(s_sz, t_sz); > > > + if (t_off < p_off || !t_sz) { > > > + swap(t_off, p_off); > > > + swap(t_sz, p_sz); > > > + } > > > } > > > - memcpy(dst, src, t_off); > > > + > > > + memcpy(dst, src, p_off); > > > + memcpy(dst + p_off + p_sz, > > > + src + p_off + p_sz, > > > + t_off - p_off - p_sz); > > > memcpy(dst + t_off + t_sz, > > > src + t_off + t_sz, > > > s_off - t_off - t_sz); > > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > > > index beb96866f34d..83d71d6912f5 100644 > > > --- a/kernel/bpf/syscall.c > > > +++ b/kernel/bpf/syscall.c > > > @@ -30,6 +30,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > #include > > > #include > > > #include > > > @@ -230,6 +231,60 @@ static int bpf_map_update_value(struct bpf_map *map, struct fd f, void *key, > > > return err; > > > } > > > > > > +static int copy_map_value_cmp(const void *_a, const void *_b) > > > +{ > > > + const u32 a = *(const u32 *)_a; > > > + const u32 b = *(const u32 *)_b; > > > + > > > + /* We only need to sort based on offset */ > > > + if (a < b) > > > + return -1; > > > + else if (a > b) > > > + return 1; > > > + return 0; > > > +} > > > + > > > +void copy_map_value_slow(struct bpf_map *map, void *dst, void *src, u32 s_off, > > > + u32 s_sz, u32 t_off, u32 t_sz) > > > +{ > > > + struct bpf_map_value_off *tab = map->ptr_off_tab; /* already set to non-NULL */ > > > + /* 3 = 2 for bpf_timer, bpf_spin_lock, 1 for map->value_size sentinel */ > > > + struct { > > > + u32 off; > > > + u32 sz; > > > + } off_arr[BPF_MAP_VALUE_OFF_MAX + 3]; > > > + int i, cnt = 0; > > > + > > > + /* Reconsider stack usage when bumping BPF_MAP_VALUE_OFF_MAX */ > > > + BUILD_BUG_ON(sizeof(off_arr) != 88); > > > + > > > + for (i = 0; i < tab->nr_off; i++) { > > > + off_arr[cnt].off = tab->off[i].offset; > > > + off_arr[cnt++].sz = sizeof(u64); > > > + } > > > + if (s_sz) { > > > + off_arr[cnt].off = s_off; > > > + off_arr[cnt++].sz = s_sz; > > > + } > > > + if (t_sz) { > > > + off_arr[cnt].off = t_off; > > > + off_arr[cnt++].sz = t_sz; > > > + } > > > + off_arr[cnt].off = map->value_size; > > > + > > > + sort(off_arr, cnt, sizeof(off_arr[0]), copy_map_value_cmp, NULL); > > > > Ouch. sort every time we need to copy map value? > > sort it once please. 88 bytes in a map are worth it. > > Especially since "slow" version will trigger with just 2 kptrs. > > (if I understand this correctly). > > Ok, also think we can reduce the size of the 88 bytes down to 55 bytes (32-bit > off + 8-bit size), and embed it in struct map. Then the shuffling needed for > timer and spin lock should also be gone. We can probably make this copy_map_value_slow to be the only function. I suspect + /* There is always at least one element */ + memcpy(dst, src, off_arr[0].off); + /* Copy the rest, while skipping other regions */ + for (i = 1; i < cnt; i++) { + u32 curr_off = off_arr[i - 1].off + off_arr[i - 1].sz; + u32 next_off = off_arr[i].off; + + memcpy(dst + curr_off, src + curr_off, next_off - curr_off); + } is faster than the dance we currently do in copy_map_value with a bunch of if-s.