Speaker
Description
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 software-defined networking (SDN) backends, as well as high-performance memory buffers like dmabuf and devmem.
When a host undergoes a kexec warm reboot, virtual devices (such as netkit, veth, netkit, bonding) and software transport layers (RXE for Soft-RoCE, SIW for Soft-iWARP) lose their underlying kernel configurations, ring buffer indices, and state machines. Concurrently, zero-copy performance mechanisms like dmabuf and TCP devmem face the challenge of memory lifecycle decoupling—how to safely hand over page references and page tables across the kexec boundary without freeing the buffers or causing in-flight DMA corruption.
This interactive session aims to pinpoint the architectural constraints of virtual network state preservation and explore how to extend the Kexec HandOver (KHO) framework or complementary Live Update Orchestrators (LUO) to solve these stateful handover and high-performance memory recycling dilemmas.
Key Questions / Discussion Topics:
1. Generic State Management
Can we provide a generic state-management framework for Live Update, so individual drivers do not need to implement the full LUO/KHO callback lifecycle independently?
2. Preservation Ordering & Quiescence
How should Live Update coordinate the preservation of DMA-BUF with PCI, VFIO, and IOMMU, especially when fence cleanup and DMA quiescence require these components to remain operational?
3. State Synchronization
How can we synchronize restored DMA-BUF kernel state with hardware state, including IOMMU mappings, device contexts, rings, interrupts, and doorbells, without causing data corruption or IOMMU faults?
4. Dependency & Recovery Ordering
How can Live Update enforce dependencies and restore ordering across components, such as PCI → VFIO → IOMMU and NIC → Netkit → RXE?
5. Failure Handling & Dependency Status
How should DMA-BUF Live Update determine whether its dependencies are successfully preservable, and what should happen if PCI, VFIO, or IOMMU Live Update cannot be preserved?