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[80.230.85.71]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5ad2e1b49aasm3607701e87.77.2026.06.16.08.51.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Jun 2026 08:51:46 -0700 (PDT) Date: Tue, 16 Jun 2026 11:51:42 -0400 From: "Michael S. Tsirkin" To: Ding Hui Cc: Gavin Shan , qemu-arm@nongnu.org, qemu-devel@nongnu.org, peterx@redhat.com, alex@shazbot.org, richard.henderson@linaro.org, peter.maydell@linaro.org, berrange@redhat.com, philmd@oss.qualcomm.com, philmd@mailo.com, david@kernel.org, clg@redhat.com, pbonzini@redhat.com, phrdina@redhat.com, jugraham@redhat.com, liugang24219@sangfor.com.cn, shan.gavin@gmail.com Subject: Re: [PATCH v3 1/2] system/memory: Use qemu_ram_{copy, move}() in ram device region accessors Message-ID: <20260616115004-mutt-send-email-mst@kernel.org> References: <20260616052552.389021-1-gshan@redhat.com> <20260616052552.389021-2-gshan@redhat.com> <20260616021153-mutt-send-email-mst@kernel.org> <20260616054555-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: jL9vX-VMXv0P8aSXrEIiTvvCepNMCmtJRPdP7A7rk8M_1781625108 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org On Tue, Jun 16, 2026 at 08:50:27PM +0800, Ding Hui wrote: > > What is the question, exactly? That's why I made the list of 11 issues. > > Is that unclear, somehow? Another reason to include that, maybe. > > > > We can take the e1000 issue on aarch64 for example: > > Link: https://lore.kernel.org/qemu-devel/20260527091711.3901-1-liugang24219@sangfor.com.cn/ > > The software allocate ring buffer for hardware to receive packet. > In normal case, the hardware fill the RX ring descriptor, and with status DD bit=1 (Descriptor Done), > then the ownership of the ring descriptor is converted to software, after the software consume > the descriptor, it will write status DD bit=0 and give it back to hardware to refill data. > > pci_dma_write calls memcpy at the underlying level, and on aarch64 with glibc 2.24+, > the memcpy/memmove implementation uses a branchless sequence that copies > the same byte three times when count == 1. Yes this is issue 11: 10. on non-x86 memcpy will do multiple overlapping stores even for single byte writes. E.g. it does it to avoid extra branches. This is causing issues in practice. -- MST