Support QEMU's host C code being compiled in Thumb mode (as some gccs do by default)
KVM
Common
Countless fixes ported over from qemu-kvm, core is now shared with that tree, i.e. has the same quality
Pimped up threading model, now fully synchronized with qemu-kvm tree
Removed dependency on external kernel headers, all supported KVM features are now built into the binary
x86
Paravirtual kvmclock fixes
Stable guest TSC across migration
Support for SMEP CPU feature
Support for VIA CPU features
Reworked & fixed MCE support
Devices
virtio-serial
Various fixes for hot-unplug of ports
Disallow generic ports at id 0: port number 0 is reserved for console ports for backward compatibility; '-device virtserialport,nr=0' is now not allowed.
Allow re-use of a chardev after a port using it gets unplugged
Add trace events
RTC
MC146818 (for PCs): Follow host clock resets to the past immediately (instead of freezing the clock)
Balloon
Fix use-after-free bug that lead to qemu crash when 'balloon 0' was issued in the monitor
Multiple balloon devices are now forbidden; it doesn't make sense to have more than one device at a time.
Negative balloon values are now rejected. The previous behaviour was to silently deflate the balloon (negative values were parsed as very high positive values)
Fix memory leaks on exit or unplug of the virtio-balloon device
Fix migration after unplugging of the virtio-balloon device. Previously, the destination aborted migration for a missing section.
Block Layer
Added missing -drive options to the man page
Expose live snapshot support in QMP using the snapshot-blkdev-sync command (commit d967b2f)
Fixed removable media support to not cache the media size. Before this fix, the guest OS would see the old CD-ROM size even after changing the medium. (commit 46a4e4e)
qemu-img
qemu-img convert and rebase now support the -p option which enables progress display (commit 6b837bc)
qemu-img commit, convert and rebase now support the -t option which allows to specify a cache mode that should be used to open the image (commit 661a0f7)
The performance of qemu-img convert has been improved (commit f6a00aa)
Block Drivers
qcow2
Improved the performance of creating/deleting internal snapshots (commit 93913df)
Instead of the device ide-drive for both hard disks and CD-ROMs we have now separate ide-hd and ide-cd devices (commit 1f56e32)
Fixed confusion between the Busmaster IDE status register and internal error state, which could lead to crashes (commit def9379)
CDROM Emulation
Many fixes to comply with ATAPI specification
GET_EVENT_STATUS_NOTIFICATION: Implement 'media' subcommand that helps report tray open/close, media present/absent states to guests. Newer Linux guests (kernels 2.6.38+) rely on this command to revalidate discs.
Major code refactoring and cleanup
virtio-blk
The serial number of the drive is now exposed as a qdev property (commit a8686a9)
SCSI Disk Emulation
Instead of the device scsi-disk for both hard disks and CD-ROMs we have now separate scsi-hd and scsi-cd devices (commit b443ae6)
Networking
User space (slirp)
Fixed DHCP support in restrict (host-only) mode
Ping packet forwarding to external hosts via unprivileged ICMP sockets of Linux 3.0