ChangeLog/6.0

System emulation

Incompatible changes

• The deprecated pc-1.0, pc-1.1, pc-1.2 and pc-1.3 machine types have been removed (they likely could not be used for live migration from old QEMU versions anymore anyway). Use a newer pc-i440fx-... machine type instead.
• The change QMP command has been removed. Use blockdev-change-medium or change-vnc-password instead.
• The -show-cursor option has been removed. Use -display sdl,show-cursor=on instead.
• The -realtime option has been removed. Use -overcommit mem-lock=on|off' instead.
• The -tb-size option has been removed. Use -accel tcg,tb-size=... instead.
• The configure script --enable/disable-git-update args have been replaced with --with-git-submodules

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.

• The --enable-fips option has been deprecated. Consumers wishing to have FIPS compliance must build QEMU with libcrypt and gnutls, NOT nettle.

Arm

• QEMU now supports emulation of the Arm-v8.1M architecture and the Cortex-M55 CPU
• Emulation of the ARMv8.4-TTST extension is now supported
• Emulation of the ARMv8.4-SEL2 extension is now supported
• Emulation of the PAuth extension now supports an optional IMPDEF pauth algorithm which is not cryptographically secure but is much faster to compute
• Emulation of the ARMv8.4-DIT extension is now supported. (Note that QEMU's implementation does not in fact provide any timing guarantees; emulation of the extension is purely to support guests which query its presence and work with the PSTATE.DIT bit.)
• Emulation of the ARMv8.5-MemTag extension is now supported for linux-user. (It was already supported for system emulation.)
• xlnx-zynqmp boards now support the Xilinx ZynqMP CAN controllers
• the sbsa-ref board now supports Cortex-A53/57/72 cpus
• the xlnx-versal board now has USB support
• the sabrelite board emulation has been improved and it can now run U-Boot
• the npcm7xx boards support more devices: ADC, PWM, SMBus
• the gdbstub's representation of SVE registers allows GDB to properly handle aliasing
• the 'virt' board now provides a mechanism for secure (EL3) firmware to power down or reset the system
• documentation for vexpress/versatile has been updated with example kernel configuration/command lines

MIPS

• Loongson-3 "virt" machine added

PowerPC

• Deprecated 'compat' property of server class POWER cpus removed (use the 'max-cpu-compat' machine option instead)
• You can now explicitly choose 'kvm_type=auto' rather than only being able to do that by not setting it at all.
• powernv machine type now defaults to 1GiB of RAM
• powernv now allows an external BMC

RISC-V

• Improve the sifive_u DTB generation
• Add QSPI NOR flash to Microchip PFSoC
• Fix a bug in the Hypervisor HLVX/HLV/HSV instructions
• Fix some mstatus mask defines
• Ibex PLIC improvements
• OpenTitan memory layout update (Breaking change)
• Initial steps towards support for 32-bit CPUs on 64-bit builds
• Automate GDB XML generation (should fix GDB E14 errors)
• Sifive OTP handle OTP access failures
• Correctly generate a PMP failure when no PMP entry is configured
• Fix 32-bit Linux boot problems with DTB placement

s390

• Linux kernels built with clang-11 and clang-12 now work correctly under tcg

x86

• TCG can emulate the PKS feature (protection keys for supervisor pages).
• Intel PT can now be exposed to KVM guests when CPUID.(EAX=14,ECX=0).ECX[LIP] (bit 31) is 1. Previous versions only supported Intel PT when LIP=0
• New sev-inject-launch-secret QMP command
• The WHPX accelerator supports accelerated APIC ("-accel whpx,kernel-irqchip=on")
• The microvm machine type got a second (optional) ioapic for the virtio-mmio irq lines, which in turn allows 24 (instead of 8) virtio-mmio devices.
• Support for running SEV-ES encrypted guests.

Device emulation and assignment

Multi-process QEMU

• The experimental -machine x-remote and -device x-pci-proxy-dev options have been added to support out-of-process device emulation. Currently only the lsi53c895 SCSI device can be emulated in a separate process. Please see the documentation and Features/MultiProcessQEMU for details on this experimental feature, which is still subject to change.

NVDIMM

• nvdimm devices will check that -device nvdimm,unarmed=on option is used when using -object memory-backend-file,readonly=on

PCI/PCIe

• The 'pvpanic-pci' device is a PCI-device version of the 'pvpanic' ISA device, which can be used on systems with only PCI and no ISA bus as a mechanism for the guest to inform QEMU that it has paniced.

USB

• Support for writing usb traffic to package capture files for inspection with wireshark has been added. Use the new pcap=<file> property added to all usb devices to enable this.

virtiofs

• Security fix for CVE-2020-35517 - prevent opening of special files
• Performance improvements with new guest kernel feature FUSE_KILLPRIV_V2

Semihosting

• Added support for RiscV (ARM style semihosting)
• Added support for HEAPINFO, ELAPSED, TICKFREQ, TMPNAM and ISERROR to semihosting

GUI

• vnc: support for cursors with alpha channel has been added.
• vnc: support for extended desktop resize has been added. With virtio-vga the guest display should adapt to vnc client window resizes.

GDBStub

• the stub now supports the Xfer:auxv:read for Linux user guests
• the GDB stubs now uses the "official" gdb representation for SVE registers

TCG Plugins

• New API for querying details about HW access
• Bug fix to avoid double counting some instructions when using -icount

Memory backends

• hostmem-file: added readonly=on|off option

Migration

• New feature (experimental): Background RAM snapshot from Andrey Gruzdev; using the Linux UFFD-WP feature, enabling fixed size snapshots even with busy guests
• QMP native snapshot commands -snapshot-{save,load,delete}
• query/info-migrate now display the migration blocker status and the reasons for blocking.

Monitor

QMP

• A new command set-action has been introduced. The command generalizes watchdog-set-action and allows changes to all the settings of the (also new) -action command line option.
• New OOB commands yank and query-yank have been introduced. The yank command allows to recover from a hanging QEMU by shutting down sockets for example. See the QMP documentation for more information. The query-yank command lists the available things to yank.
• The new QMP commands load-snapshot, save-snapshot and delete-snapshot provide a mechanism for managing internal qcow2 snapshots, that was previously only available via HMP commands loadvm, savevm and delvm
• The block-bitmap-mapping parameter within the QMP command migrate-set-parameters gained a transform member for adjusting the persistence of a bitmap on the destination.

Block device backends and tools

• For its background operation, the backup job now runs multiple asynchronous requests in parallel
• The stream block job now uses the copy-on-read block driver (and its new bottom option) to let copy-on-read help make progress even when using any of block-stream’s base, base-node, or bottom options
• The new QMP commands load-snapshot, save-snapshot and delete-snapshot provide a mechanism for managing internal qcow2 snapshots, that was previously only available via HMP commands loadvm, savevm and delvm
• When qemu operates as an NBD server that will service multiple clients (whether via QMP nbd-server-start, qemu-storage-daemon, or qemu-nbd), it now allows a larger backlog of pending clients. When using a Unix socket, this avoids a client failing to connect due to EAGAIN.
• qemu-nbd --shared=0 now works to allow an unlimited number of shared clients to a single NBD server.

Miscellaneous

• A new command line option -action, with suboptions panic, shutdown, reboot and watchdog. -action subsumes the pre-existing options -no-shutdown (-action panic=pause,shutdown=pause), -no-reboot (-action reboot=shutdown) and -watchdog-action; plus, it allows the user to choose whether guest panic should pause the guest (-action panic=pause), shut it down (-action panic=poweroff, the default) or be ignored (-action panic=none).
• A new generic machine option confidential-guest-support was added to (partially) unify configuration for AMD SEV memory encrypt, POWER PEF and s390 Protected Virtualization, plus future methods of protecting a guest from eavesdropping by a compromised hypervisor.

User-mode emulation

Hexagon

Added support for the Qualcomm Hexagon processor, in linux-user mode only.

For more information, see our presenation from the 2019 KVM Forum or the README file

TCG

• Added support for Apple Silicon hosts (macOS)

Build Information

• Support for building with link-time optimization or with LLVM control-flow integrity
• New "gtags" build target for developers
• checkpatch now better handles commit ids when checking

Container Based Builds

• handling of binfmt_misc containers has improved the handling of dynamically linked binaries pointing at symlinks

Testing and CI

• shippable support has been removed
• more testing has been migrated from Travis to GitLab

Known issues

• see Planning/6.0