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Tsirkin" To: David Woodhouse Cc: Richard Cochran , Peter Hilber , linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-rtc@vger.kernel.org, "Ridoux, Julien" , virtio-dev@lists.linux.dev, "Luu, Ryan" , "Chashper, David" , "Mohamed Abuelfotoh, Hazem" , "Christopher S . Hall" , Jason Wang , John Stultz , netdev@vger.kernel.org, Stephen Boyd , Thomas Gleixner , Xuan Zhuo , Marc Zyngier , Mark Rutland , Daniel Lezcano , Alessandro Zummo , Alexandre Belloni , qemu-devel , Simon Horman Subject: Re: [PATCH] ptp: Add vDSO-style vmclock support Message-ID: <20240726084836-mutt-send-email-mst@kernel.org> References: <20240725122603-mutt-send-email-mst@kernel.org> <0959390cad71b451dc19e5f9396d3f4fdb8fd46f.camel@infradead.org> <20240725163843-mutt-send-email-mst@kernel.org> <20240725170328-mutt-send-email-mst@kernel.org> <20240725174327-mutt-send-email-mst@kernel.org> <9261e393083bcd151a017a5af3345a1364b3e0f3.camel@infradead.org> <20240726015613-mutt-send-email-mst@kernel.org> <2e427b102d8fd899a9a3db2ec17a628beb24bc01.camel@infradead.org> Precedence: bulk X-Mailing-List: virtio-dev@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <2e427b102d8fd899a9a3db2ec17a628beb24bc01.camel@infradead.org> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Fri, Jul 26, 2024 at 09:35:51AM +0100, David Woodhouse wrote: > But for this use case, we only need a memory region that the hypervisor > can update. We don't need any of that complexity of gratuitously > interrupting all the vCPUs just to ensure that none of them can be > running userspace while one of them does an update for itself, > potentially translating from one ABI to another. The hypervisor can > just update the user-visible memory in place. Looks like then your userspace is hypervisor specific, and that's a problem because it's a one way street - there is no way for hypervisor to know what does userspace need, so no way for hypervisor to know which information to provide. No real way to fix bugs. -- MST