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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: <20240725015120-mutt-send-email-mst@kernel.org> References: <14d1626bc9ddae9d8ad19d3c508538d10f5a8e44.camel@infradead.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <14d1626bc9ddae9d8ad19d3c508538d10f5a8e44.camel@infradead.org> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wed, Jul 24, 2024 at 06:16:37PM +0100, David Woodhouse wrote: > From: David Woodhouse > > The vmclock "device" provides a shared memory region with precision clock > information. By using shared memory, it is safe across Live Migration. > > Like the KVM PTP clock, this can convert TSC-based cross timestamps into > KVM clock values. Unlike the KVM PTP clock, it does so only when such is > actually helpful. > > The memory region of the device is also exposed to userspace so it can be > read or memory mapped by application which need reliable notification of > clock disruptions. > > Signed-off-by: David Woodhouse one other thing worth mentioning is that this design can't work with confidential computing setups. By comparison, mapping e.g. a range in a PCI BAR would work for these setups. Is there a reason this functionality is not interesting for confidential VMs? -- MST