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[80.230.85.71]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4601f2dcbe3sm76782849f8f.8.2026.06.11.09.13.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Jun 2026 09:13:16 -0700 (PDT) Date: Thu, 11 Jun 2026 12:13:14 -0400 From: "Michael S. Tsirkin" To: Peter Maydell Cc: Gavin Shan , Peter Xu , Pavel Hrdina , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-devel@nongnu.org, qemu-arm@nongnu.org, jugraham@redhat.com, shan.gavin@gmail.com, Alex Williamson , David Hildenbrand Subject: Re: [PATCH RFCv1] virtio: Inherit max bounce buffer size from bus parent if possible Message-ID: <20260611120325-mutt-send-email-mst@kernel.org> References: <20260610121026-mutt-send-email-mst@kernel.org> <1e9515c9-7e32-4d95-9b73-aab8bf10bddc@redhat.com> <20260611012217-mutt-send-email-mst@kernel.org> <3726a607-6cac-41f1-b402-0eed7c4e3fe3@redhat.com> <20260611023428-mutt-send-email-mst@kernel.org> <0c3f1dba-3b2c-43c5-b181-1426f6da0951@redhat.com> <20260611093049-mutt-send-email-mst@kernel.org> <20260611110156-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: <20260611110156-mutt-send-email-mst@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 8jsUKG0olAL75NI3_Fs2sQOj4_MHHVDG-KKsiJ6CrJ8_1781194398 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; 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_H5=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 Thu, Jun 11, 2026 at 11:05:35AM -0400, Michael S. Tsirkin wrote: > > If and where we need to provide guarantees about "this access will > > really definitely only do this size access and it won't break it > > apart or anything like that" then we need to either be using compiler > > atomics or else inline asm. BTW you meant intrinsics, of course, but speaking of atomics, they do not work on device ram, or not yet. E.g. kvm does not support them when exiting to qemu I think (only if emulating within kernel) and it prints "emulating exchange as write". We are quite far from "arbitrary access" even on pure device RAM. -- MST