ChangeLog/5.1

System emulation

New deprecated options and features

Consult the "Deprecated Features" chapter of the QEMU System Emulation User's Guide for the full list of historically deprecated features/options.

Arm

• Emulation of the following architecture features is now implemented:
  • ARMv8.2-TTS2UXN
• xlnx-versal-virt: machine now supports RTC and SD
• New board model: sonorapass-bmc
• Host memory errors can now be reported to AArch64 KVM guests via ACPI when using the 'virt' board (this is disabled by default; enable with '-machine ras=on')
• All the imx6 and imx7 machines now support the watchdog timer device
• The Raspberry Pi boards now support the USB controller. Note that for the moment booting a Raspbian guest kernel requires adding "dwc_otg.fiq_fsm_enable=0" to the guest kernel command line.

PowerPC

• The "label-size" property is now mandatory for NVDIMMs on the "pseries" machine type (the PAPR specification only supports labelled NVDIMMs)
• NVLink2 devices can no longer be unplugged. This is not possible on real hardware, and was never supported by the guest side drivers, so this makes things safer.
• We no longer use reconfiguration reboots to handle difficult cases during CAS option negotiation
• Added an interface to inject POWER style NMIs
• scv and rfscv instructions now supported in TCG
• Can now select POWER10 with the "pseries" machine type

RISC-V

• OpenSBI loaded by default for virt and sifive_u machines
• The spike_v1.9.1 and spike_v1.10 machines have been removed
• The rv32gcsu-v1.9.1, rv32gcsu-v1.10.0, rv64gcsu-v1.9.1, rv64gcsu-v1.10.0, rv32imacu-nommu and rv64imacu-nommu CPUs have been removed
• The RISC-V privilege spec 1.09.1 has been removed
• Spike machine supports more then 1 CPU
• Spike machine supports the -bios option
• OpenSBI updated to v0.7
• linux-usermode improvements
• Support for the SiFive E34 CPU
• 32-bit improvements for the sifive_u machine
• Corrections to the Hypervisor extension page table walking
• Expose a "serial" property for the sifive_u machine that specifys the board serial number
• Support for the Ibex CPU
• Support for the OpenTitan machine (opentitan)

s390

• Support for protected virtualization aka secure execution has been merged (KVM only)
  • The host needs to be a z15 or Linux One III with at least Linux 5.7
• vfio-ccw devices no longer require that the issuer sets the 'allow prefetch' bit in the ORB
  • The host kernel still may reject those requests, though (5.7 or older)
  • Note that a channel program that actually relies on no prefetching being done will still fail. In practice, though, this only applies to IPL CCWs, and that process is accommodated by the s390-ccw bios already.
  • The 'force-orb-pfch' property to force setting of the 'allow prefetch' bit by vfio-ccw itself still exists.

Tricore

• Add gdb stub
• Fix segfault due to uninitialized ctx->env ptr

Device emulation and assignment

ACPI

• QEMU now exposes a WAET (Windows ACPI Emulated Devices Table) to guests -

this reduces virtualization overhead for non-enlightened windows (Vista and later) guests by avoiding guest workarounds for an unreliable ACPI PM timer.

• QEMU now supports both cold and hot plug of nvdimms for ARM Guests with ACPI.

PCI/PCIe

Attempts to hotplug devices into a pci slot with hotplug disabled will now return an error instead of adding the device without notifying the guest.

virtio

• TCG guests can now use vhost-user daemons (including virtiofsd). There are corner cases which could interfere with TCG's self-modifying code detection although this shouldn't occur with sane guest OSes.

virtiofs

• virtiofsd:
  • Security fix: CVE-2020-10717, resource exhaustion of host fd's
  • Jailing improvements
  • Ensure that existing mounts under the shared directory are visible to the guest

Character devices

• The 'socket' backend now supports the abstract namespace for UNIX sockets, with the new 'abstract' and 'tight' options

GUI

• Windows keyboard fixes for GTK and SDL

GDBStub

• bug fix to m68k gdbstub
• linux-user now supports unix socket for debugging (needs a new gdb)
• some tests for the stub added to check-tcg
• wider watchpoints are supported in system emulation mode

Migration

• Migration of block dirty bitmaps when not using -blockdev now avoids using generated node names; without this fix, a migration attempt that included bitmaps and was attempted while a mirror job was active (which was a common scenario with older libvirt that did not use -blockdev but set up an NBD mirror for storage migration in parallel) would generally fail due to the difference in generated node names between the source and destination.

Block device backends and tools

• Optional zstd compression for qcow2 (enable with compression_type=zstd as a creation option)
• Fixed regression with 'qemu-nbd -c /dev/nbd0' keeping inherited stderr open (introduced in 4.1)
• 'qemu-img map' gained --start-offset and --max-length options for mapping only a subset of a file
• 'qemu-img' gained a new command mode 'bitmap' for manipulating persistent bitmaps in qcow2 files
• 'qemu-img measure' now reports the space occupied by persistent bitmaps in qcow2 files
• 'qemu-img convert' gained a new --bitmaps option for convenience in copying bitmaps alongside guest-visible content of qcow2 files

Miscellaneous

• HMP: qom-set now takes JSON for the value. This means it no longer accepts numbers of the form '100M'
• HMP: new command: qom-get can now be used to read the value of a qom property

TCG

• support for wider watchpoints in system emulation

Build Information

Container Based Builds

• Updated aarch64 container for bullseye based compiler for testing newer features

Build Dependencies

• Now requires GTK 3.22 or newer

Testing

• vm-build tests can now use alternatives to genisoimage (cdrkit)

Known issues

• see Planning/5.1