From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C324C2ECE96; Wed, 8 Oct 2025 15:16:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759936582; cv=none; b=Od48FcspQsgundhqnvjQfYJ5zd4h6El+BTwgRU1ERsq+Gd0ppI/1Z6zvJZXIr89kEmQpux7I5PF+UrC0uXgw0YE8s+3E+zkp7WIGJJpJOlx1y1ASJoKwvj0YtEW8jHhQiwLWSM72tdQkXYOvxAHfYnMD39Qzqam5++Qy5sbSQpc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759936582; c=relaxed/simple; bh=qht7upbZcN8Fp3kBFgjhtYFX7m/ywbptenojVx6vypA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jLsmuMpqVSAZZl4NF46cmVx0gHhlNC/NAvgZs4zhnqQUM83QTO+WxLk7Ur8zGUnibwvjw1gj0voBmXrKqfz4AHum0JbkZhjQDrw+F6HTlmnVgUcUoPNdT/NkfyVjj3QIOgOMTaG2nUIudxqtW3OHEV/RmyZFg/ya4/UaLXIXTpk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=RxpKTFHX; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="RxpKTFHX" Received: from [10.18.189.204] (unknown [167.220.238.76]) by linux.microsoft.com (Postfix) with ESMTPSA id 4A3D82038B69; Wed, 8 Oct 2025 08:16:08 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 4A3D82038B69 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1759936573; bh=5TpYtkIM3vm8SzLYGq6t368MueIPPKh5A747g7RJJ0U=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RxpKTFHXFhVvEfRgr19RhxzXiDCrYzYhGBJokLgnbduQD3cxckwoNxv9ZFW1avHy7 Cblr5iHoIFLvpXkvprGZmChticXo+37TJB/N0wzRll3bMIiopL1rNZ+bti6JHCl+td IcZMcV0y8ALXfV3AybyU2JJ53jjg04i+rNqpIOz0= Message-ID: <9d886861-2e1f-4ea8-9f2c-604243bd751b@linux.microsoft.com> Date: Wed, 8 Oct 2025 20:46:05 +0530 Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next] net: mana: Linearize SKB if TX SGEs exceeds hardware limit To: Eric Dumazet Cc: kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com, andrew+netdev@lunn.ch, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, longli@microsoft.com, kotaranov@microsoft.com, horms@kernel.org, shradhagupta@linux.microsoft.com, ernis@linux.microsoft.com, dipayanroy@linux.microsoft.com, shirazsaleem@microsoft.com, linux-hyperv@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, gargaditya@microsoft.com, ssengar@linux.microsoft.com References: <20251003154724.GA15670@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> Content-Language: en-US From: Aditya Garg In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 03-10-2025 21:45, Eric Dumazet wrote: > On Fri, Oct 3, 2025 at 8:47 AM Aditya Garg > wrote: >> >> The MANA hardware supports a maximum of 30 scatter-gather entries (SGEs) >> per TX WQE. In rare configurations where MAX_SKB_FRAGS + 2 exceeds this >> limit, the driver drops the skb. Add a check in mana_start_xmit() to >> detect such cases and linearize the SKB before transmission. >> >> Return NETDEV_TX_BUSY only for -ENOSPC from mana_gd_post_work_request(), >> send other errors to free_sgl_ptr to free resources and record the tx >> drop. >> >> Signed-off-by: Aditya Garg >> Reviewed-by: Dipayaan Roy >> --- >> drivers/net/ethernet/microsoft/mana/mana_en.c | 26 +++++++++++++++---- >> include/net/mana/gdma.h | 8 +++++- >> include/net/mana/mana.h | 1 + >> 3 files changed, 29 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c >> index f4fc86f20213..22605753ca84 100644 >> --- a/drivers/net/ethernet/microsoft/mana/mana_en.c >> +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c >> @@ -20,6 +20,7 @@ >> >> #include >> #include >> +#include >> >> static DEFINE_IDA(mana_adev_ida); >> >> @@ -289,6 +290,19 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev) >> cq = &apc->tx_qp[txq_idx].tx_cq; >> tx_stats = &txq->stats; >> >> + BUILD_BUG_ON(MAX_TX_WQE_SGL_ENTRIES != MANA_MAX_TX_WQE_SGL_ENTRIES); >> + #if (MAX_SKB_FRAGS + 2 > MANA_MAX_TX_WQE_SGL_ENTRIES) >> + if (skb_shinfo(skb)->nr_frags + 2 > MANA_MAX_TX_WQE_SGL_ENTRIES) { >> + netdev_info_once(ndev, >> + "nr_frags %d exceeds max supported sge limit. Attempting skb_linearize\n", >> + skb_shinfo(skb)->nr_frags); >> + if (skb_linearize(skb)) { > > This will fail in many cases. > > This sort of check is better done in ndo_features_check() > > Most probably this would occur for GSO packets, so can ask a software > segmentation > to avoid this big and risky kmalloc() by all means. > > Look at idpf_features_check() which has something similar. Hi Eric, Thank you for your review. I understand your concerns regarding the use of skb_linearize() in the xmit path, as it can fail under memory pressure and introduces additional overhead in the transmit path. Based on your input, I will work on a v2 that will move the SGE limit check to the ndo_features_check() path and for GSO skbs exceding the hw limit will disable the NETIF_F_GSO_MASK to enforce software segmentation in kernel before the call to xmit. Also for non GSO skb exceeding the SGE hw limit should we go for using skb_linearize only then or would you suggest some other approach here? Regards, Aditya