Description
Proposal
Live Update is a specialized reboot process where selected devices are kept operational and kernel state is preserved and recreated across a kexec. For devices, DMA and interrupts may continue during the reboot.
The primary use-case of Live Update is to enable hypervisor updates in cloud environments with minimal disruption to running virtual machines. During a Live Update, a VM can pause and its state is stored to memory while the hypervisor reboots. PCIe devices attached to those VMs (such as GPUs, NICs, and SSDs), are kept running during the Live Update. After the reboot, VMs are recreated and restored from memory, reattached to devices, and resumed. The disruption is limited to the time it takes to complete this entire process.
With Live Update infrastructure in place, other use-cases may emerge, like for example preserving the state of GPU doing LLM, freezing running containers with CRIU, and preserving large in-memory databases.
The Live Update and state persistence functionality touch on different parts of the kernel and this microconference aims to bring together people from different subsystems. Upstream support for Live Updates is still in its infancy and there are a lot of unsolved aspects that will benefit from direct communication.
Key problems that will be discussed:
Support for memfd/guest_memfd/hugetlb/tmpfs Preserving the state of VFIO, IOMMUFD, and IOMMU drivers. Preserving vCPUs and Orphaned Virtual Machines LUO systemd integration Integration of Live Update with PCI and Device Model Leveraging suspend/resume functionality for device state preservation Optimizing kernel shutdown and boot times.
Last year achievements:
Following โMemory persistence over kexecโ BoF at LPC 2024 we we landed support for Kernel KHO, LUO, and memfd preservation.
Expanding the BoF to a full blown MC helped defining key data structures required for Live Update stability and isolating them into a dedicated kho/abi/ directory under include/linux.
Duing 2025 edition of Live Update MC we finalized the objectives and design for making KHO stateless and itโs now transitioned to a radix tree for memory preservation.
Key attendees:
- Alex Graf
- Alex Williamson
- Ben Herrenschmidt
- Bjorn Helgaas
- David Matlack
- David Rientjes
- David Woodhouse
- Evangelos Petrongonas
- Jason Gunthorpe
- Josh Hilke
- Luca Boccassi
- Michaล Cลapiลski
- Mike Rapoport
- Pasha Tatashin
- Pratyush Yadav
- Samiullah Khawaja
- Vipin Sharma
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Mr Luca Boccassi (Microsoft)06/10/2026, 15:00
systemd v261 added native support for LUO. System services, user services and nspawn containers can preserve data across kexec in a simple and transparent manner, using the existing File Descriptor Store API.
This talk will explore what is implemented and how to use it, and what are the next steps.
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Samiullah Khawaja06/10/2026, 15:15
Preserving subsystem state across a live update introduces a complex challenge: managing the dependencies of File Descriptors. Interconnected subsystemsโsuch as VFIO and IOMMUFD with a lot of shared state, IOMMUFD's dependency on memory providers memfd/guest_memfd or KVMfd/guest_memfd dependency requires preservation ordering to guarantee state immutability and performance.
Currently, the...
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Mr Prasanna Kumar T S M (Microsoft), Srivatsa Bhat (Microsoft)06/10/2026, 15:30
Motivation:
Kexec Hand-Over (KHO) helps minimize downtime during kernel updates by preserving state across the kexec reboot. However, there are some scenarios which need a deeper form of reboot to be effective -- for example, performing a firmware update or a device-tree refresh, or even to avoid known hardware/platform bugs that make the kexec path itself unreliable. In such cases, the...
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Logan Odell (Google), Pratyush Yadav06/10/2026, 15:50
Data that is serialized and preserved through a live update may have formatting differences between two kernels. This can affect the compatibility between two kernels when trying to perform a Live Update. Current efforts have been to use compatibility strings with implicit version numbers, like "memfd-v2" to help provide compatibility data. Changes to the formatting of the preserved data may...
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Tarun Sahu (Google)06/10/2026, 16:10
Guest_memfd is a specialized, guest-first memory subsystem within the Linux kernel, specifically designed for KVM. It provides an isolated file-descriptor-based approach to managing Virtual Machine memory.
For this MC, I want to propose the topic on Preservation of guest_memfd with LUO.
I will discuss the current development on guest_memfd preservation during kernel Liveupdate and (If...
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Michaล Cลapiลski (Google)06/10/2026, 17:00
Many use-cases of live-update require it to be fast. For cloud providers, executing host kernel updates without impacting guest workloads demands low-downtime live-update reboots.
We will discuss what improvements were already done to the Linux kernel, the ongoing work and future plans. This talk will also explain to developers how to configure their systems to achieve the best reboot performance.
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David Matlack (Google)06/10/2026, 17:15
Live Update minimizes downtime by allowing PCI devices, like those assigned to VMs via VFIO, to continue operating during a host kernel upgrade. The recently proposed v7 patch series introduces the foundational PCI core support for Live Update. By leveraging LUO to preserve the list of preserve devices, the infrastructure allows PCI devices to maintain uninterrupted memory transactions to/from...
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Pranjal Shrivastava, Samiullah Khawaja06/10/2026, 17:30
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The current IOMMU Live Update framework establishes the mechanism for preserving IOMMU hardware state and translation units (HWPTs) across a live update. By utilizing the IOMMUFD and Kernel Handover (KHO) framework. This session talks about the current state of Liveupdate IOMMU and the upcoming features, challenges and enhancements.
The session dives deeper into the design challenges... -
Vipin Sharma (Google)06/10/2026, 17:50
Live Update enables hypervisor updates with minimal guest downtime by preserving VM state across
kexec. While memory preservation (via KHO/LUO) covers VM RAM, pass-through PCIe devices assigned to VMs (e.g., GPUs, NICs, NVMe, accelerators) require kernel support to maintain device state across the reboot boundary.This talk presents the design of VFIO Live Update (Phase 1, recently posted...
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yanjun zhu06/10/2026, 18:10
As cloud infrastructure scales and Confidential Computing adoption increases, host-level Live Update via kexec has become vital for maintaining zero-downtime operations. While progress has been made in preserving guest memory (guest_memfd, hugetlb) and hardware device states (VFIO), a critical gap remains in the network stack: preserving virtual networking topologies and stateful...
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