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[34.150.200.138]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7d389e1291asm65377997b3.12.2026.05.26.11.37.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 May 2026 11:37:08 -0700 (PDT) Date: Tue, 26 May 2026 14:37:07 -0400 From: Pasha Tatashin To: Alexander Graf , "Andersen, Tycho" , Anthony Yznaga , Baolu Lu , David Hildenbrand , David Matlack , "Heyne, Maximillian" , James Gowans , Jason Gunthorpe , Mike Rapoport , Pankaj Gupta , Pasha Tatashin , Pratyush Yadav , Praveen Kumar , Vipin Sharma , Vishal Annapurve , "Woodhouse, David" , Luca Boccassi , Samiullah Khawaja , Jork Loeser Cc: linux-mm@kvack.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [Hypervisor Live Update] Notes from May 18, 2026 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260526_113710_658579_CA353FA8 X-CRM114-Status: GOOD ( 14.07 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org Hi everybody, Here are the notes from the last Hypervisor Live Update call that happened on Monday, May 18. Thanks to everybody who was involved! These notes are intended to bring people up to speed who could not attend the call as well as keep the conversation going in between meetings. ----->o----- Administrative Updates & LPC 2026 To kick off the meeting, it was announced that I will be taking over the management of the Hypervisor Live Update meetings going forward, with David Matlack serving as a backup for scheduling conflicts. Thank you to David Rientjes for running these up to this point! Additionally, the Live Update micro-conference has been officially accepted for LPC 2026. Attendees are highly encouraged to submit topics and proposals as the micro-conference will be listed among the available tracks. ----->o----- Systemd LUO Integration Systemd: Luca's patch has been successfully merged into systemd. This allows for the use of the fdstore to pass file descriptors across a live update, which is a major milestone for adoption. ----->o----- MSHV + KHO Pratyush and I discussed using the Radix Tree as a sparse bitmap for MSHV. To improve code modularity, we agreed to explore establishing a new lib directory to house common data structures (e.g., blocked linked lists, memory management structures) that can be easily shared by the other KHO users. ----->o----- KHO, Boot Time & HugeTLB Preservation LSF/MM/BPF Debrief: Pratyush provided an update on the HugeTLB preservation talk. The consensus is that VFS hooks must be made aware of the freezing process. Generic fallocate and setattr functions will be updated to return errors up the stack immediately, rather than requiring individual filesystems to handle freezing logic. Boot Time Performance: The struct page initialization patch is ready for the upcoming merge window. Broader boot time optimizations (like refactoring the buddy memory allocator) remain a future project. HugeTLB Preservation: Progress is currently gated by the I/O freezing work and the fallback allocation strategy (which helps the kernel discover free memory ranges lacking preserved pages for HugeTLB allocation). Pratyush has requested reviews to unblock this. ----->o----- VFIO, PCI Core, & IOMMU Persistence PCI Core: David Matlack sent v5 last week and is planning to send v6 this week after incorporating recent feedback. He is currently awaiting reviews from Bjorn on the refactored code. IOMMU Persistence: Samiullah Khawaja noted that v2 of the series received positive feedback from Intel. He is preparing v3 and has also submitted related series for VFIO self-tests and DMA lock preservation. IOMMU Development Roadmap: Samiullah outlined the following milestones, noting that architecture-specific streams can run in parallel once foundational hooks land: Milestone 1 (Foundations): Intel IOMMU state persistence. Milestone 2 (Multi-Arch): ARM SMMU persistence; Intel 2nd stage hitless domain replacement. Milestone 3 (PASID): PASID support across core and driver components. Milestone 4 (Virtualization): vIOMMU and nested IOMMU virtualization (Intel VT-d, then ARM/AMD). ----->o----- guest_memfd & Confidential VMs guest_memfd: The team discussed the guest_memfd HugeTLB enlightenment RFC, highlighting challenges with handling shared vs. private mappings (since LU currently only supports fully shared guest memory). There is an ongoing debate regarding flags and whether one-time creation flags need dynamic conversions. CVMs: We acknowledged that supporting Confidential VMs will act as a massive stress test for KVM due to the high volume of 4K page table preservations. This topic was tabled for a future meeting. ----->o----- Process Memory Persistence (CRIU & Kexec) Maximilian Heyne presented a PoC using CRIU to preserve process memory across a kexec reboot without writing image files to disk, successfully keeping 10GB of memory in a memfd. ----->o----- Next meeting will be on Monday, June 1 at 8am PDT (UTC-7), everybody is welcome: https://meet.google.com/rjn-dmzu-hgq Topics for the next meeting: - Vipin and David Matlack roadmap for PCI and VFIO changes to solicit upstream feedback - Status of I/O freezing implementations and HugeTLB fallback allocation patches - PCI core changes v6 review and next steps - IOMMU persistence v3 and roadmap progress - Updates on vm_splice investigations for CRIU memory preservation - later: KHO support for Confidential VMs including page table preservation and pinning - later: versioning support for luo to negotiate - later: KHO enlightenment for ASI - later: testing methodology to allow downstream consumers to qualify that live update works from one version to another - later: reducing blackout window during live update