ChangeLog/4.0

System emulation

Incompatible changes

• The "handle" option to -fsdev and -virtfs has been removed. The "local" or "proxy" options should be used instead.

New deprecated options and features

• cpu-add QMP/HMP command
• machine-types pc-0.12, pc-0.13, pc-0.14 and pc-0.15

Consult the "Deprecated Features" appendix for the full list of historically deprecated features/options.

Arm

• Allow AArch64 processors to boot from a kernel placed over 4GB into RAM
• arm: Implement the ARMv8.1-HPD extension
• arm: Implement the ARMv8.2-AA32HPD extension
• arm: Implement the ARMv8.1-LOR extension (as the trivial "no limited ordering regions provided" minimum)
• arm: Implement the ARMv8.3-PAuth extension
• The micro:bit board supports more devices: timer, GPIO and RNG
• The cubieboard model now implements the 'A' SRAM
• The BLK_MAX register in the TZ MPC device now reports the correct value
• The u-boot "noload" image type is now supported for the Arm virt board
• stm32f2xx_usart: Do not update data register when device is disabled
• virt board ACPI tables: COHACC override flag now correctly set in IORT SMMUv3 node
• AArch32 exception return is fixed to permit a switch from Mon->Hyp mode
• ftgmac100: implement the new MDIO interface on Aspeed SoC
• Emulation of the ARM PMU has been improved

MIPS

• Build for MIPS n32 hosts fixed.

RISC-V

• The virt board now supports PCI and USB.

s390

• vfio-ap now no longer inhibits usage of memory ballooners
• zPCI devices now provide some instruction counters to the guest (for a Linux guest, check /sys/kernel/debug/pci/<function>/statistics)

x86

• The HAX accelerator is now supported for Linux hosts too.

Device emulation and assignment

Block devices

• IDE/via: Implement PCI IDE mode

Network devices

• pvrdma: Add support for RDMA MAD
• pvrdma: Removed the dev-caps-max-sge parameter

Crypto subsystem

• The block storage encryption backends are now capable of using multiple threads for encryption/decryption

GUI

• The VNC server will no longer accidentally delete its UNIX listener socket when clients disconnect

Monitor

• QMP can now execute a few commands "out of band". This is useful for postcopy recovery. For details, see docs/interop/qmp-spec.txt.
• query-qmp-schema reflects QEMU's build configuration more closely. For instance, stuff related to replication is properly absent when QEMU was built with --disable-replication.
• QMP events SHUTDOWN and RESET now carry a reason
• New QMP command query-current-machine
• QMP/HMP command system_wakeup now fails when the guest isn't suspended, or doesn't even support suspend.
• QMP/HMP command cpu-add is now deprecated
• New QMP commands block-dirty-bitmap-enable, block-dirty-bitmap-disable, and block-dirty-bitmap-merge, plus enhancements to transaction, nbd-server-add, and block-dirty-bitmap-add, allow a management application to perform incremental backups with an NBD client as a consumer learning which portions of the disk were changed while the bitmap was enabled. The experimental commands x-block-dirty-bitmap-enable, x-block-dirty-bitmap-disable, x-block-dirty-bitmap-merge and x-nbd-server-add-bitmap were removed in favor of the stable commands.

Block devices and tools

• Improved tracing and error diagnostics for NBD code
• Fix infinite loop in DMG image format
• A new --bitmap option to qemu-nbd allows the exposure of a persistent dirty bitmap for a qcow2 image not in use by a guest, in a simpler manner than the older procedure of using QMP commands to a temporary qemu process attached to the file.
• A new --list option to qemu-nbd enables the ability to probe a remote NBD server for information about what it is exporting.

Tracing

• The new qemu-trace-stap script makes it convenient to collect traces without writing SystemTap scripts. See "man qemu-trace-stap" for details.

Miscellaneous

• QEMU's builtin gdbstub now supports the gdb multiprocess extension. Boards which have more than one cluster of CPUs (like the 'xlnx-zcu102' board when run with '-smp 6') will report them as being two processes (each of which has one thread per CPU in the cluster). You will need at least GDB 7.2. Attach to QEMU with a GDB command sequence like:

target extended :1234

add-inferior

inferior 2

attach 2

and then the "info threads" command should show 2 processes.

• QEMU will default to KVM when compiled with --disable-tcg or when launched from an executable whose name ends with "kvm".

TCG

• SoftFloat acceleration - where it is safe to do so, the softfloat helpers will use host floating-point instructions yielding significant performance increases
• Dynamic sizing of software TLBs, yielding noticable performance increases
• Host support for 64-bit RISC-V.

Build Information

Build Dependencies

• QEMU now requires at least GCC version 4.8 or Clang version 3.4 (or Clang from Xcode 5.1) to be built
• Running the QEMU testsuite now requires the Perl Test::Harness module. Most Linux and BSD distributions however install it by default together with Perl.

Known issues

• see Planning/4.0