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[204.195.96.226]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-842b84fb8ddsm2033647a12.42.2024.12.19.20.59.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Dec 2024 20:59:55 -0800 (PST) Date: Thu, 19 Dec 2024 20:59:52 -0800 From: Stephen Hemminger <stephen@networkplumber.org> To: "Wangyunjian(wangyunjian,TongTu)" <wangyunjian@huawei.com> Cc: "dev@dpdk.org" <dev@dpdk.org>, "maxime.coquelin@redhat.com" <maxime.coquelin@redhat.com>, "chenbox@nvidia.com" <chenbox@nvidia.com>, "Lilijun (Jerry)" <jerry.lilijun@huawei.com>, "xiawei (H)" <xiawei40@huawei.com>, wangzengyuan <wangzengyuan@huawei.com>, "stable@dpdk.org" <stable@dpdk.org> Subject: Re: [PATCH 1/1] vhost: fix a double fetch when dequeue offloading Message-ID: <20241219205952.08c09ae7@hermes.local> In-Reply-To: <f72d79f98e984283933a8955278bcee0@huawei.com> References: <91dc12662805a3867413940f856ba9454b91c579.1734588243.git.wangyunjian@huawei.com> <20241219081532.345c7536@hermes.local> <f72d79f98e984283933a8955278bcee0@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: patches for DPDK stable branches <stable.dpdk.org> List-Unsubscribe: <https://mails.dpdk.org/options/stable>, <mailto:stable-request@dpdk.org?subject=unsubscribe> List-Archive: <http://mails.dpdk.org/archives/stable/> List-Post: <mailto:stable@dpdk.org> List-Help: <mailto:stable-request@dpdk.org?subject=help> List-Subscribe: <https://mails.dpdk.org/listinfo/stable>, <mailto:stable-request@dpdk.org?subject=subscribe> Errors-To: stable-bounces@dpdk.org On Fri, 20 Dec 2024 02:17:12 +0000 "Wangyunjian(wangyunjian,TongTu)" <wangyunjian@huawei.com> wrote: > > -----Original Message----- > > From: Stephen Hemminger [mailto:stephen@networkplumber.org] > > Sent: Friday, December 20, 2024 12:16 AM > > To: Wangyunjian(wangyunjian,TongTu) <wangyunjian@huawei.com> > > Cc: dev@dpdk.org; maxime.coquelin@redhat.com; chenbox@nvidia.com; > > Lilijun (Jerry) <jerry.lilijun@huawei.com>; xiawei (H) <xiawei40@huawei.com>; > > wangzengyuan <wangzengyuan@huawei.com>; stable@dpdk.org > > Subject: Re: [PATCH 1/1] vhost: fix a double fetch when dequeue offloading > > > > On Thu, 19 Dec 2024 14:38:28 +0800 > > Yunjian Wang <wangyunjian@huawei.com> wrote: > > > > > - hdr = (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr); > > > + rte_memcpy((void *)(uintptr_t)&tmp_hdr, > > > + (void *)(uintptr_t)buf_vec[0].buf_addr, > > > + sizeof(struct virtio_net_hdr)); > > > } > > > > Do not introduce more rte_memcpy of a fixed size. > > You don't need that many casts! > > Why can you not use a structure assignment here. > > The virtio_hdr is a shared component, and other fields within it are read > multiple times. This can potentially result in a double fetch scenario. The point is do a copy, but not with rte_memcpy. Also you need a rte_compiler_barrier() anyway.