This release has been tracked in v50.0 group of our roadmap project.

Configurable Nested Virtualization Option on x86_64

The nested=on|off option has been added to --cpu to allow users
to configure nested virtualization support in the guest on x86_64
hosts (for both KVM and MSHV). The default value is on to maintain
consistency with existing behavior. (#7408)

Compression Support for QCOW2

QCOW2 support has been extended to handle compression clusters based on
zlib and zstd. (#7462)

Notable Performance Improvements

Performance of live migration has been improved via an optimized
implementation of dirty bitmap maintenance. (#7468)

Live Disk Resizing Support for Raw Images

The /vm.resize-disk API has been introduced to allow users to resize block
devices backed by raw images while a guest is running. (#7476)

Developer Experience Improvements

Significant improvements have been made to developer experience and
productivity. These include a simplified root manifest, codified and
tightened Clippy lints, and streamlined workflows for cargo clippy and
cargo test. (#7489)

Improved File-level Locking Support

Block devices now use byte-range advisory locks instead of whole-file
locks. While both approaches prevent multiple Cloud Hypervisor instances
from simultaneously accessing the same disk image with write
permissions, byte-range locks provide better compatibility with network
storage backends. (#7494)

Logging Improvements

Logs now include event information generated by the event-monitor
module. (#7512)

Notable Bug Fixes

• Fix several issues around CPUID in the guest (arch/x86_64: fix cpuid leaf 0x1 EBX bits 23-16 #7485, Fix V2 extended topology enumeration APIC ID reporting #7495, arch: Mask (out) extended AMX features #7508)
• Fix snapshot/restore for Windows Guest (hypervisor: kvm: Save KVM HyperV SynIC emulation state #7492)
• Respect queue size in block performance tests (performance-metrics: Respect queue size in block tests #7515)
• Fix several Serial Manager issues (Serial Manager fixes #7502)
• Fix several seccomp violation issues (seccomp: allow sendto for vsock thread #7477, seccomp: allow sendto for vfio_user devices #7497, seccomp: add arch_prctl syscall for amx #7518)
• Fix various issues around block and qcow (block: qcow: Set OFLAG_COPIED bit in L1 entries for QCOW2 spec compli… #7526, block: qcow2: Flush the buffer explicitly when writing pointer table #7528, block: qcow: Cluster Leak Fixes #7537, block: allow VIRTIO_BLK_T_GET_ID for read-only devices #7546,
  block: qcow: Add missing flush in write_refcount_block #7549)
• Retrieve MSRs list correctly on MSHV (hypervisor: mshv: retrieve MSRs list correctly #7543)
• Fix live migration (and snapshot/restore) with AMX state (hypervisor: AMX state snapshot and restore support #7534)

Contributors

Many thanks to everyone who has contributed to our release:

• Anatol Belski anbelski@linux.microsoft.com
• Anirudh Rayabharam anrayabh@microsoft.com
• Bo Chen bchen@crusoe.ai
• Changyuan Lyu changyuanl@google.com
• Chengyu Fu chengyu.fu@linux.alibaba.com
• Connor Brewster cbrewster@hey.com
• Demi Marie Obenour demiobenour@gmail.com
• Eugene Korenevsky ekorenevsky@aliyun.com
• Julian Stecklina julian.stecklina@cyberus-technology.de
• Matt Moriarity matt@mattmoriarity.com
• Muminul Islam muislam@microsoft.com
• Oliver Anderson oliver.anderson@cyberus-technology.de
• Pascal Scholz pascal.scholz@cyberus-technology.de
• Philipp Schuster philipp.schuster@cyberus-technology.de
• Praveen K Paladugu prapal@linux.microsoft.com
• Rob Bradford rbradford@rivosinc.com
• Sebastien Boeuf seb@rivosinc.com
• Songqian Li sionli@tencent.com
• Stefan Nürnberger stefan.nuernberger@cyberus-technology.de
• Thomas Prescher thomas.prescher@cyberus-technology.de
• Wei Liu liuwe@microsoft.com