ChangeLog/5.2

IMPORTANT NOTE: in this release we have switched our build system to internally use Meson. Building should be broadly unchanged for most users, but please see the 'Build Information' section of the changelog for details and for the list of new build dependencies you might now need to install.

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.

In particular, note that the Unicore32 and lm32 guest support have been deprecated and will be removed in a future version. They are now only built if explicitly enabled in --target-list.

Arm

• ARMv8.2 FEAT_FP16 (half-precision floating point) is now implemented for AArch32 emulation (AArch64 already supported this)
• The SMMUv3 model now supports SMMUv3.2 range invalidation
• The sbsa-ref board now has an embedded controller model for guest powerdown and reboot requests
• Support for KVM on 32-bit host CPUs (deprecated in 5.0) has now been removed. (32-bit KVM guests on 64-bit hosts remain supported.)
• Two new board models in the mps2 family: mps2-an386 (Cortex-M4 based) and mps2-an500 (Cortex-M7 based)
• New Nuvoton iBMC board models: npcm750-evb, quanta-gsj
• The 'max' CPU now implements a 48-bit physical address size when using TCG emulation.
• The 'virt' board supports kvm-steal-time (enabled by default for virt-5.2 and on) so that a guest OS can account for time when its CPUs were not running due to the host not scheduling the corresponding vCPU threads.

HPPA

• Added power button emulation
• Boots NetBSD
• Boots old Linux CDs, e.g debian-0.5 and debian-0.6.1
• Artist framebuffer fixes when running dtwm on HP-UX
• Artist graphics allows screen resolution up to 2048 x 2048 pixels
• fw_cfg interface added

PowerPC

• The pseries machine now respects the nvdimm= machine option (previously NVDIMMs could be attached even with nvdimm=off)
• The pseries machine now does a better job of reflecting the user specified NUMA distances in the guest (PAPR limitations mean it's still a pretty poor approximation, though)
• We now fail more gracefully if attempting to run an HPT guest as a nested KVM guest (which isn't supported in the kernel for now)
• spapr_vscsi should now properly report that it does not support hotplug
• The pnv machine now allows firmware images up to 16MiB, instead of just 4 MiB (this matches the limit on physical FSP machines)

RISC-V

• Improvements to the Ibex (OpenTitan) PLIC
• OpenSBI v0.8 included by default
• Generic OpenSBI platform used when no -bios argument is supplied
• Support for a noMMU Linux kernel with the `-kernel` option
• A dummy L2 cache controller for the sifive_u is now included
• Support for the SiFive OTP device
• PMPCFG CSR setting bug fixed for RV64
• Improvements to the floating point helpers
• Experimental Hypervisor support updated to v0.6.1 and bug fixes
• Support for NUMA sockets on Virt and Spike Machines
• Support for the Microchip PolarFire SoC Icicle Kit
• Fix for crash seen when running 'poweroff' command on virt machine

s390

• KVM: The diagnose 0x318 instruction is now supported.
• TCG: More instructions that were introduced with the z14 are now emulated.

x86

• A new KVM feature which improves the handling of asynchronous page faults is available with -cpu ...,kvm-async-pf-int. This requires Linux 5.8.

Xtensa

• DFPU coprocessor with single and double precision floating point opcodes is now supported
• NMI is now supported

Device emulation and assignment

NVMe

• Add support for mandatory features of version 1.3 of the NVM Express specification
• Add support for the Abort, Asynchronous Event Request and Get Log Page commands

SMBIOS

• The OEM Strings data can now be loaded from a file

9pfs

• Significant performance improvement of Treaddir requests.
• A performance warning is now logged on host side if 'msize' is set to a very small value, which especially includes Linux 9P clients not having any user specified 'msize' parameter at all. Simply setting 'msize' (on client/guest side) to any value larger than 8192 will cause the warning to disappear. See msize documentation for details.

Migration

• A new 'block-bitmap-mapping' migration parameter is added, allowing finer control of which bitmaps to migrate, even when node names differ between source and destination.
• Migration over 'vsock' is now allowed, for nested environments or hosts with hardware that looks like a vsock.
• A new 'calc-dirty-rate'/'query-dirty-rate' call gathers an approximation of the rate at which the guest is dirtying RAM and thus gives an idea about whether precopy migration is likely to proceed.
• The default migration bandwidth has been increased to 1Gbps; users are still encouraged to tune it to their own hardware.
• TLS+multifd is now supported for higher bandwidth encrypted migration.

Monitor

QMP

• Command block_resize no longer blocks the main loop.

HMP

• Command block_resize no longer blocks the main loop.

Block device backends and tools

• qcow2 files now support extended L2 entries that allow subcluster-based allocation (enable with extended_l2=on when creating the image).
• Using qemu as an NBD client has fewer scenarios where network timeouts stall guest execution
• More explicit errors are reported when use of O_DIRECT fails

Tracing

• Add support of dtrace backend on macOS

Miscellaneous

• The roms/edk2 submodule and the bundled edk2 binaries have been updated to edk2-stable202008.

User-mode emulation

• ppc64abi32-linux-user is deprecated and only built when explicitly enabled in--target-list
• tilegx-linux-user is deprecated and only built when explicitly enabled in--target-list
• better reporting when we can't mmap the guest_base we want on systems without MAP_FIXED_NOREPLACE

Build Information

• The build system is now partly based on Meson. However, building is still done with configure and make as in previous versions of QEMU.
• Binaries for emulators are placed in the root build directory, for example as qemu-system-ppc instead of ppc-softmmu/qemu-system-ppc. Symbolic links from the old binary are preserved to simplify the transition.
• In-tree builds are not supported anymore. The build system will try to cater for ./configure && make && make install by building QEMU in a directory named build, but you are encouraged to switch to out-of-tree builds instead.
• ivshmem-client and ivshmem-server are not installed anymore. They are merely examples, and not to be used in production.
• QEMU installations are now relocatable. For example, if QEMU is configured with bindir=/usr/local/bin and datadir=/usr/local/share, when QEMU is launched as /opt/local/qemu-5.2/bin/qemu-system-x86_64 it will look automatically for data files in /opt/local/qemu-5.2/share. Note that directories configured outside the prefix (as is often the case for /etc and /var) will not be relocated! Previously this was done only under Windows and only for emulators.

Python

• Python 3.6 or newer is now required to build QEMU.

Container Based Builds

• All Debian 9 based cross-compiler containers have been updated to Debian 10

Build Dependencies

• Ninja 1.7 or newer is now required to build QEMU.

Windows

• qemu-nbd is now built on mingw, and works for simple cases even if it can't duplicate the full functionality available on Unix systems

Known issues

• see Planning/5.2