From mboxrd@z Thu Jan 1 00:00:00 1970 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 8166761FFE; Sun, 11 May 2025 00:41:31 +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=1746924091; cv=none; b=QRTWgjbWYwZdiQ5aIMk2Iy3ah3MsBoKw/YGYx4ikD1C4ZnvVLklN7IfOo9EEP9J+izSyvzZ8WI0vxLBx0B5BORZUlwjgPz+sxS24G/gbjZFHwyVruG6pPt8KIk62/IOJbHOt3jxMJitgW4ptvAJDtIXxchKZLQW4ExY4ZgTFEYU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746924091; c=relaxed/simple; bh=Er5gc2hUENA4gCdJhtwjHn21KMcLdvxvQg5p2KS53YU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=qw7Afkv+ULMIzIW+WzmNkmm3Fm9Em6RrDIpBLaOBvNiG2BMPyMclUnj2Px3hUkvxe9kIdk9de0KZfndtyz7fdS8ENttvKkjsguCNCFmW73MX5fLFv6iTd73wmf+Znmd51fMDjYjqyhM0jjstX+GAi+YuQD59TgwgZYvflMEOwlo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tscoOcsq; 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="tscoOcsq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E7173C4CEF2; Sun, 11 May 2025 00:41:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746924090; bh=Er5gc2hUENA4gCdJhtwjHn21KMcLdvxvQg5p2KS53YU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tscoOcsq7YtK4+n3cVHEr3de+HfaNOpYztWa9Umb5OukdiQO7MTKvPIKjnN3YiL8G Truwd0tO3gJoUvEuYwi2LlghvslZ4Gcuykja8KiO6PmNBLguFwNrZRfagm/7Ug5eJY 0zfccwrKcbUVJf3A32FZHOFMJUiFs0EIuKOYRX0X1nDP79Y33AjhOkWVTWj9MQIH21 vkIpbidhbGefydXm8iPEJEUgnwAFMJKNAijRvfCxh8brkpqOLXyx2a7yYKx4Qyo+q5 eS+IEz1otWLeACSjUsfy6vKdtFAuq8ZjW38lfLWMpZcNOKLIIqlpFWQ9B465Lvte5V xf/NuyBFuaUWA== From: Eric Biggers To: netdev@vger.kernel.org Cc: linux-nvme@lists.infradead.org, linux-sctp@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, Daniel Borkmann , Marcelo Ricardo Leitner , Sagi Grimberg , Ard Biesheuvel Subject: [PATCH net-next 02/10] net: add skb_crc32c() Date: Sat, 10 May 2025 17:41:02 -0700 Message-ID: <20250511004110.145171-3-ebiggers@kernel.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250511004110.145171-1-ebiggers@kernel.org> References: <20250511004110.145171-1-ebiggers@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Eric Biggers Add skb_crc32c(), which calculates the CRC32C of a sk_buff. It will replace __skb_checksum(), which unnecessarily supports arbitrary checksums. Compared to __skb_checksum(), skb_crc32c(): - Uses the correct type for CRC32C values (u32, not __wsum). - Does not require the caller to provide a skb_checksum_ops struct. - Is faster because it does not use indirect calls and does not use the very slow crc32c_combine(). According to commit 2817a336d4d5 ("net: skb_checksum: allow custom update/combine for walking skb") which added __skb_checksum(), the original motivation for the abstraction layer was to avoid code duplication for CRC32C and other checksums in the future. However: - No additional checksums showed up after CRC32C. __skb_checksum() is only used with the "regular" net checksum and CRC32C. - Indirect calls are expensive. Commit 2544af0344ba ("net: avoid indirect calls in L4 checksum calculation") worked around this using the INDIRECT_CALL_1 macro. But that only avoided the indirect call for the net checksum, and at the cost of an extra branch. - The checksums use different types (__wsum and u32), causing casts to be needed. - It made the checksums of fragments be combined (rather than chained) for both checksums, despite this being highly counterproductive for CRC32C due to how slow crc32c_combine() is. This can clearly be seen in commit 4c2f24549644 ("sctp: linearize early if it's not GSO") which tried to work around this performance bug. With a dedicated function for each checksum, we can instead just use the proper strategy for each checksum. Signed-off-by: Eric Biggers --- include/linux/skbuff.h | 1 + net/core/skbuff.c | 73 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 74 insertions(+) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index f3e72be6f634..33b33bb18aa6 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -4192,10 +4192,11 @@ extern const struct skb_checksum_ops *crc32c_csum_stub __read_mostly; __wsum __skb_checksum(const struct sk_buff *skb, int offset, int len, __wsum csum, const struct skb_checksum_ops *ops); __wsum skb_checksum(const struct sk_buff *skb, int offset, int len, __wsum csum); +u32 skb_crc32c(const struct sk_buff *skb, int offset, int len, u32 crc); static inline void * __must_check __skb_header_pointer(const struct sk_buff *skb, int offset, int len, const void *data, int hlen, void *buffer) { diff --git a/net/core/skbuff.c b/net/core/skbuff.c index d73ad79fe739..b9900cc16a24 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -62,10 +62,11 @@ #include #include #include #include #include +#include #include #include #include #include @@ -3626,10 +3627,82 @@ __wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset, BUG_ON(len); return csum; } EXPORT_SYMBOL(skb_copy_and_csum_bits); +#ifdef CONFIG_NET_CRC32C +u32 skb_crc32c(const struct sk_buff *skb, int offset, int len, u32 crc) +{ + int start = skb_headlen(skb); + int i, copy = start - offset; + struct sk_buff *frag_iter; + + if (copy > 0) { + copy = min(copy, len); + crc = crc32c(crc, skb->data + offset, copy); + len -= copy; + if (len == 0) + return crc; + offset += copy; + } + + if (WARN_ON_ONCE(!skb_frags_readable(skb))) + return 0; + + for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) { + int end; + skb_frag_t *frag = &skb_shinfo(skb)->frags[i]; + + WARN_ON(start > offset + len); + + end = start + skb_frag_size(frag); + copy = end - offset; + if (copy > 0) { + u32 p_off, p_len, copied; + struct page *p; + u8 *vaddr; + + copy = min(copy, len); + skb_frag_foreach_page(frag, + skb_frag_off(frag) + offset - start, + copy, p, p_off, p_len, copied) { + vaddr = kmap_atomic(p); + crc = crc32c(crc, vaddr + p_off, p_len); + kunmap_atomic(vaddr); + } + len -= copy; + if (len == 0) + return crc; + offset += copy; + } + start = end; + } + + skb_walk_frags(skb, frag_iter) { + int end; + + WARN_ON(start > offset + len); + + end = start + frag_iter->len; + copy = end - offset; + if (copy > 0) { + copy = min(copy, len); + crc = skb_crc32c(frag_iter, offset - start, copy, crc); + len -= copy; + if (len == 0) + return crc; + offset += copy; + } + start = end; + } + BUG_ON(len); + + return crc; +} +EXPORT_SYMBOL(skb_crc32c); +#endif /* CONFIG_NET_CRC32C */ + __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len) { __sum16 sum; sum = csum_fold(skb_checksum(skb, 0, len, skb->csum)); -- 2.49.0