From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 3C21B4EDCAC; Thu, 17 Sep 2026 16:55:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789664151; cv=none; b=Ka1ZdRHNxrxUk+XPUVIwJwHsXDabWKURTtNob4jWhTCdbWjfMbIAsdaMQyOjtRiYeXCacFwBMrdx466H6o/+ObKakMaZ8UKg6nbo39cCDJlZr92bwm8bkXlULW4hqcn3rd+NcNx7SnSwqjV8vFZaruvov6S0R0U8XoiPk4xTa1Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789664151; c=relaxed/simple; bh=ibxS1jIK7TXYiwWUj2nG92zsaxoE2PpDqi4xxwe+9/w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=TnCrpc/cilxXDxV0DC+izNQlMX/nXnbok+6ZVPDWyEwv7RY9pX9vv5fnZEAROScFASmzaQxODuKDMORBsRYHssIV9Shu+eh5J7NW79sn7ZIRjntaSzz6787hW5DfLakgsNwtiMeYkvMx8zzvpjXEBpBkSsN1jhiJVa+9LtCKyAg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=xCfl5d53; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="xCfl5d53" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8F20D1F000FF; Thu, 17 Sep 2026 16:55:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789664150; bh=S5gkYmU8UI4U/TvOoF1vPR+1BLFmwUAfh0/A6yVDzAg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=xCfl5d53i0kaDnjlLq7BziCkrtFYoFsjFgQEITdzhbqzJxGDlyC5ylCjtIWO8KKDS DjRLa9d0lkXlUGO2XLehGV9nYlTvQslpUiXlBSgUeVrL7YDNwOwNpffT3G/p0pG1kK JoaATDZB68D5g0MLr9t453yPcC6s9OozEGSULVv0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Rosen Penev , Paolo Abeni , Sasha Levin Subject: [PATCH 6.18 0276/1250] net: ibm: emac: Reserve VLAN header in MJS limit Date: Thu, 17 Sep 2026 16:01:11 +0100 Message-ID: <20260917151559.616992266@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260917151551.901433442@linuxfoundation.org> References: <20260917151551.901433442@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Rosen Penev [ Upstream commit 0906c117f81c2ae6e6dbfa82719f79c75e1c9325 ] The IBM EMAC programs its Maximum Jumbo Size (MJS) drop threshold from ndev->mtu directly. The hardware sizes the threshold against the L2 frame minus the ethernet header, but does not discount the 802.1Q tag, so a frame carrying a VLAN tag and a full 1500-byte payload exceeds MJS by exactly 4 bytes and is dropped. This is normally hidden because JPSM (and therefore the MJS check) only engages when the MTU is raised above ETH_DATA_LEN. With the qca8k DSA tagger the conduit MTU is bumped by QCA_HDR_LEN to 1502 during dsa_conduit_setup(), which is enough to enable JPSM and expose the off-by-VLAN-tag in the limit. Pad MJS by VLAN_HLEN so a VLAN-tagged full-MTU frame passes. Reported on Meraki MX60 (qca8k switch): tagged VLAN traffic drops at 1500-byte payload, while 1496 bytes works and untagged 1500 bytes works. Assisted-by: Claude:Opus-4.7 Signed-off-by: Rosen Penev Link: https://patch.msgid.link/20260526202247.13823-1-rosenp@gmail.com Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- drivers/net/ethernet/ibm/emac/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c index e1047915e101e..f48568140480e 100644 --- a/drivers/net/ethernet/ibm/emac/core.c +++ b/drivers/net/ethernet/ibm/emac/core.c @@ -30,6 +30,7 @@ #include #include #include +#include #include #include #include @@ -457,7 +458,7 @@ static inline u32 emac_iff2rmr(struct net_device *ndev) if (emac_has_feature(dev, EMAC_APM821XX_REQ_JUMBO_FRAME_SIZE)) { r &= ~EMAC4_RMR_MJS_MASK; - r |= EMAC4_RMR_MJS(ndev->mtu); + r |= EMAC4_RMR_MJS(ndev->mtu + VLAN_HLEN); } return r; -- 2.53.0