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[76.102.12.149]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2c10b2e6c30sm3345405eec.25.2026.03.20.08.01.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Mar 2026 08:01:34 -0700 (PDT) Date: Fri, 20 Mar 2026 08:01:33 -0700 From: Stanislav Fomichev To: Maciej Fijalkowski Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, magnus.karlsson@intel.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, larysa.zaremba@intel.com, aleksander.lobakin@intel.com, bjorn@kernel.org Subject: Re: [PATCH v2 net 2/8] xsk: respect tailroom for ZC setups Message-ID: References: <20260319175538.479139-1-maciej.fijalkowski@intel.com> <20260319175538.479139-3-maciej.fijalkowski@intel.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260319175538.479139-3-maciej.fijalkowski@intel.com> On 03/19, Maciej Fijalkowski wrote: > Multi-buffer XDP stores information about frags in skb_shared_info that > sits at the tailroom of a packet. The storage space is reserved via > xdp_data_hard_end(): > > ((xdp)->data_hard_start + (xdp)->frame_sz - \ > SKB_DATA_ALIGN(sizeof(struct skb_shared_info))) > > and then we refer to it via macro below: > > static inline struct skb_shared_info * > xdp_get_shared_info_from_buff(const struct xdp_buff *xdp) > { > return (struct skb_shared_info *)xdp_data_hard_end(xdp); > } > > Currently we do not respect this tailroom space in multi-buffer AF_XDP > ZC scenario. To address this, introduce xsk_pool_get_tailroom() and use > it within xsk_pool_get_rx_frame_size() which is used in ZC drivers to > configure length of HW Rx buffer. > > xsk_pool_get_tailroom() is only reserving necessary space when pool is > zc and underlying netdev supports zc multi-buffer. Rely on pool->dev > state when configuring tailroom. xsk_pool_get_rx_frame_size() inside > ndo_bpf is usually called when bringing up queues and before xsk's dma > mappings have been configured, which makes it valid to rely on > pool->dev. > > Fixes: 24ea50127ecf ("xsk: support mbuf on ZC RX") > Signed-off-by: Maciej Fijalkowski Acked-by: Stanislav Fomichev