From patchwork Wed Oct 23 15:39:20 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Puranjay Mohan X-Patchwork-Id: 13847303 X-Patchwork-Delegate: bpf@iogearbox.net Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 875331C8781; Wed, 23 Oct 2024 15:39:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729697991; cv=none; b=IsNEQZxMXmLd11uODeL3hQXzw4YVPWjFmD5J040XGxNDFbrA8NGVNgn9rNidMgsvl0SyZ5mYNP2XP/rArvYrmQ4a0CiGPKDBGRYY4dvF/i/qY5eR/4oI7PPmvfDBkoCpDbCahU/wY3tfLlHeYUAQnX6xX36TsIgLctcgR3ct4nI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729697991; c=relaxed/simple; bh=hs0lXbcOH7c9T/cGcTNkAHvTScTMvbdw0SB7nKBj1RE=; h=From:To:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=kcUdXed+z/ChqTQNtw0bSgWGVnSOyMAcC7iYt9jMScqQD0aXMaWIaq/U38JM1/7/4mQ8VxRb5UjiV8wyZxwMxejjX0aY7bqrPi265FhOTQ7xhBK99P66dXzuI+ZnHPyIHVjlz64fk2Ew+7XCiH4yWUa9WD6JuvschetVa4tQjbM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CLXkRVYM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CLXkRVYM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B94B1C4CEC6; Wed, 23 Oct 2024 15:39:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1729697991; bh=hs0lXbcOH7c9T/cGcTNkAHvTScTMvbdw0SB7nKBj1RE=; h=From:To:Subject:Date:In-Reply-To:References:From; b=CLXkRVYMKhLzKMnLaS5EdZKHPPcUn+76PrLIXutI7U7lnmOtG7xAlx/T6eUgfP9Lf iRnHCzrrhQzMSO30G8hyKYGiQlNWbYQe1UdjYh5qk3fEm4Sw4L9HlRQUGDG92IZIdR 1lPKPE9Z580GvVAMZTQ2iKxapj4MdVIlSXR425bYdCaYVAPgEfK2iu+wAQ7G9XtgXr zCWqbwuHW48kEEQtTny3dFmZrnujNEy13djB4XQ2HLJ4x+ZB3GdEHZ1J5QqqCeu5rB DdlQrflJp4OHqetFDcsmUWeCSGAL94qex3lkro+Q2P8LUDd/4rOvs7STpUIijFgyoU HbU94z2on57xA== From: Puranjay Mohan To: Albert Ou , Alexei Starovoitov , Andrew Morton , Andrii Nakryiko , bpf@vger.kernel.org, Daniel Borkmann , "David S. Miller" , Eduard Zingerman , Eric Dumazet , Hao Luo , Helge Deller , Jakub Kicinski , "James E.J. Bottomley" , Jiri Olsa , John Fastabend , KP Singh , linux-kernel@vger.kernel.org, linux-parisc@vger.kernel.org, linux-riscv@lists.infradead.org, Martin KaFai Lau , Mykola Lysenko , netdev@vger.kernel.org, Palmer Dabbelt , Paolo Abeni , Paul Walmsley , Puranjay Mohan , Puranjay Mohan , Shuah Khan , Song Liu , Stanislav Fomichev , Yonghong Song Subject: [PATCH bpf-next v2 2/4] bpf: bpf_csum_diff: optimize and homogenize for all archs Date: Wed, 23 Oct 2024 15:39:20 +0000 Message-Id: <20241023153922.86909-3-puranjay@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20241023153922.86909-1-puranjay@kernel.org> References: <20241023153922.86909-1-puranjay@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net 1. Optimization ------------ The current implementation copies the 'from' and 'to' buffers to a scratchpad and it takes the bitwise NOT of 'from' buffer while copying. In the next step csum_partial() is called with this scratchpad. so, mathematically, the current implementation is doing: result = csum(to - from) Here, 'to' and '~ from' are copied in to the scratchpad buffer, we need it in the scratchpad buffer because csum_partial() takes a single contiguous buffer and not two disjoint buffers like 'to' and 'from'. We can re write this equation to: result = csum(to) - csum(from) using the distributive property of csum(). this allows 'to' and 'from' to be at different locations and therefore this scratchpad and copying is not needed. This in C code will look like: result = csum_sub(csum_partial(to, to_size, seed), csum_partial(from, from_size, 0)); 2. Homogenization -------------- The bpf_csum_diff() helper calls csum_partial() which is implemented by some architectures like arm and x86 but other architectures rely on the generic implementation in lib/checksum.c The generic implementation in lib/checksum.c returns a 16 bit value but the arch specific implementations can return more than 16 bits, this works out in most places because before the result is used, it is passed through csum_fold() that turns it into a 16-bit value. bpf_csum_diff() directly returns the value from csum_partial() and therefore the returned values could be different on different architectures. see discussion in [1]: for the int value 28 the calculated checksums are: x86 : -29 : 0xffffffe3 generic (arm64, riscv) : 65507 : 0x0000ffe3 arm : 131042 : 0x0001ffe2 Pass the result of bpf_csum_diff() through from32to16() before returning to homogenize this result for all architectures. NOTE: from32to16() is used instead of csum_fold() because csum_fold() does from32to16() + bitwise NOT of the result, which is not what we want to do here. [1] https://lore.kernel.org/bpf/CAJ+HfNiQbOcqCLxFUP2FMm5QrLXUUaj852Fxe3hn_2JNiucn6g@mail.gmail.com/ Signed-off-by: Puranjay Mohan Acked-by: Daniel Borkmann Reviewed-by: Toke Høiland-Jørgensen --- net/core/filter.c | 37 +++++++++---------------------------- 1 file changed, 9 insertions(+), 28 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index bd0d08bf76bb8..e00bec7de9edd 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -1654,18 +1654,6 @@ void sk_reuseport_prog_free(struct bpf_prog *prog) bpf_prog_destroy(prog); } -struct bpf_scratchpad { - union { - __be32 diff[MAX_BPF_STACK / sizeof(__be32)]; - u8 buff[MAX_BPF_STACK]; - }; - local_lock_t bh_lock; -}; - -static DEFINE_PER_CPU(struct bpf_scratchpad, bpf_sp) = { - .bh_lock = INIT_LOCAL_LOCK(bh_lock), -}; - static inline int __bpf_try_make_writable(struct sk_buff *skb, unsigned int write_len) { @@ -2022,11 +2010,6 @@ static const struct bpf_func_proto bpf_l4_csum_replace_proto = { BPF_CALL_5(bpf_csum_diff, __be32 *, from, u32, from_size, __be32 *, to, u32, to_size, __wsum, seed) { - struct bpf_scratchpad *sp = this_cpu_ptr(&bpf_sp); - u32 diff_size = from_size + to_size; - int i, j = 0; - __wsum ret; - /* This is quite flexible, some examples: * * from_size == 0, to_size > 0, seed := csum --> pushing data @@ -2035,19 +2018,17 @@ BPF_CALL_5(bpf_csum_diff, __be32 *, from, u32, from_size, * * Even for diffing, from_size and to_size don't need to be equal. */ - if (unlikely(((from_size | to_size) & (sizeof(__be32) - 1)) || - diff_size > sizeof(sp->diff))) - return -EINVAL; - local_lock_nested_bh(&bpf_sp.bh_lock); - for (i = 0; i < from_size / sizeof(__be32); i++, j++) - sp->diff[j] = ~from[i]; - for (i = 0; i < to_size / sizeof(__be32); i++, j++) - sp->diff[j] = to[i]; + if (from_size && to_size) + return csum_from32to16(csum_sub(csum_partial(to, to_size, seed), + csum_partial(from, from_size, 0))); + if (to_size) + return csum_from32to16(csum_partial(to, to_size, seed)); - ret = csum_partial(sp->diff, diff_size, seed); - local_unlock_nested_bh(&bpf_sp.bh_lock); - return ret; + if (from_size) + return csum_from32to16(~csum_partial(from, from_size, ~seed)); + + return seed; } static const struct bpf_func_proto bpf_csum_diff_proto = {