diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/hyperv.txt | 13 | ||||
| -rw-r--r-- | docs/microvm.rst | 108 | ||||
| -rw-r--r-- | docs/virtio-net-failover.rst | 68 |
3 files changed, 189 insertions, 0 deletions
diff --git a/docs/hyperv.txt b/docs/hyperv.txt index 8fdf25c829..6518b716a9 100644 --- a/docs/hyperv.txt +++ b/docs/hyperv.txt @@ -184,6 +184,19 @@ enabled. Requires: hv-vpindex, hv-synic, hv-time, hv-stimer +3.17. hv-no-nonarch-coresharing=on/off/auto +=========================================== +This enlightenment tells guest OS that virtual processors will never share a +physical core unless they are reported as sibling SMT threads. This information +is required by Windows and Hyper-V guests to properly mitigate SMT related CPU +vulnerabilities. +When the option is set to 'auto' QEMU will enable the feature only when KVM +reports that non-architectural coresharing is impossible, this means that +hyper-threading is not supported or completely disabled on the host. This +setting also prevents migration as SMT settings on the destination may differ. +When the option is set to 'on' QEMU will always enable the feature, regardless +of host setup. To keep guests secure, this can only be used in conjunction with +exposing correct vCPU topology and vCPU pinning. 4. Development features ======================== diff --git a/docs/microvm.rst b/docs/microvm.rst new file mode 100644 index 0000000000..aae811a922 --- /dev/null +++ b/docs/microvm.rst @@ -0,0 +1,108 @@ +==================== +microvm Machine Type +==================== + +``microvm`` is a machine type inspired by ``Firecracker`` and +constructed after its machine model. + +It's a minimalist machine type without ``PCI`` nor ``ACPI`` support, +designed for short-lived guests. microvm also establishes a baseline +for benchmarking and optimizing both QEMU and guest operating systems, +since it is optimized for both boot time and footprint. + + +Supported devices +----------------- + +The microvm machine type supports the following devices: + +- ISA bus +- i8259 PIC (optional) +- i8254 PIT (optional) +- MC146818 RTC (optional) +- One ISA serial port (optional) +- LAPIC +- IOAPIC (with kernel-irqchip=split by default) +- kvmclock (if using KVM) +- fw_cfg +- Up to eight virtio-mmio devices (configured by the user) + + +Limitations +----------- + +Currently, microvm does *not* support the following features: + + - PCI-only devices. + - Hotplug of any kind. + - Live migration across QEMU versions. + + +Using the microvm machine type +------------------------------ + +Machine-specific options +~~~~~~~~~~~~~~~~~~~~~~~~ + +It supports the following machine-specific options: + +- microvm.x-option-roms=bool (Set off to disable loading option ROMs) +- microvm.pit=OnOffAuto (Enable i8254 PIT) +- microvm.isa-serial=bool (Set off to disable the instantiation an ISA serial port) +- microvm.pic=OnOffAuto (Enable i8259 PIC) +- microvm.rtc=OnOffAuto (Enable MC146818 RTC) +- microvm.auto-kernel-cmdline=bool (Set off to disable adding virtio-mmio devices to the kernel cmdline) + + +Boot options +~~~~~~~~~~~~ + +By default, microvm uses ``qboot`` as its BIOS, to obtain better boot +times, but it's also compatible with ``SeaBIOS``. + +As no current FW is able to boot from a block device using +``virtio-mmio`` as its transport, a microvm-based VM needs to be run +using a host-side kernel and, optionally, an initrd image. + + +Running a microvm-based VM +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +By default, microvm aims for maximum compatibility, enabling both +legacy and non-legacy devices. In this example, a VM is created +without passing any additional machine-specific option, using the +legacy ``ISA serial`` device as console:: + + $ qemu-system-x86_64 -M microvm \ + -enable-kvm -cpu host -m 512m -smp 2 \ + -kernel vmlinux -append "earlyprintk=ttyS0 console=ttyS0 root=/dev/vda" \ + -nodefaults -no-user-config -nographic \ + -serial stdio \ + -drive id=test,file=test.img,format=raw,if=none \ + -device virtio-blk-device,drive=test \ + -netdev tap,id=tap0,script=no,downscript=no \ + -device virtio-net-device,netdev=tap0 + +While the example above works, you might be interested in reducing the +footprint further by disabling some legacy devices. If you're using +``KVM``, you can disable the ``RTC``, making the Guest rely on +``kvmclock`` exclusively. Additionally, if your host's CPUs have the +``TSC_DEADLINE`` feature, you can also disable both the i8259 PIC and +the i8254 PIT (make sure you're also emulating a CPU with such feature +in the guest). + +This is an example of a VM with all optional legacy features +disabled:: + + $ qemu-system-x86_64 \ + -M microvm,x-option-roms=off,pit=off,pic=off,isa-serial=off,rtc=off \ + -enable-kvm -cpu host -m 512m -smp 2 \ + -kernel vmlinux -append "console=hvc0 root=/dev/vda" \ + -nodefaults -no-user-config -nographic \ + -chardev stdio,id=virtiocon0 \ + -device virtio-serial-device \ + -device virtconsole,chardev=virtiocon0 \ + -drive id=test,file=test.img,format=raw,if=none \ + -device virtio-blk-device,drive=test \ + -netdev tap,id=tap0,script=no,downscript=no \ + -device virtio-net-device,netdev=tap0 diff --git a/docs/virtio-net-failover.rst b/docs/virtio-net-failover.rst new file mode 100644 index 0000000000..22f64c7bc8 --- /dev/null +++ b/docs/virtio-net-failover.rst @@ -0,0 +1,68 @@ +======================== +QEMU virtio-net standby (net_failover) +======================== + +This document explains the setup and usage of virtio-net standby feature which +is used to create a net_failover pair of devices. + +The general idea is that we have a pair of devices, a (vfio-)pci and a +virtio-net device. Before migration the vfio device is unplugged and data flows +through the virtio-net device, on the target side another vfio-pci device is +plugged in to take over the data-path. In the guest the net_failover kernel +module will pair net devices with the same MAC address. + +The two devices are called primary and standby device. The fast hardware based +networking device is called the primary device and the virtio-net device is the +standby device. + +Restrictions +------------ + +Currently only PCIe devices are allowed as primary devices, this restriction +can be lifted in the future with enhanced QEMU support. Also, only networking +devices are allowed as primary device. The user needs to ensure that primary +and standby devices are not plugged into the same PCIe slot. + +Usecase +------- + + Virtio-net standby allows easy migration while using a passed-through fast + networking device by falling back to a virtio-net device for the duration of + the migration. It is like a simple version of a bond, the difference is that it + requires no configuration in the guest. When a guest is live-migrated to + another host QEMU will unplug the primary device via the PCIe based hotplug + handler and traffic will go through the virtio-net device. On the target + system the primary device will be automatically plugged back and the + net_failover module registers it again as the primary device. + +Usage +----- + + The primary device can be hotplugged or be part of the startup configuration + + -device virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:6f:55:cc, \ + bus=root2,failover=on + + With the parameter failover=on the VIRTIO_NET_F_STANDBY feature will be enabled. + + -device vfio-pci,host=5e:00.2,id=hostdev0,bus=root1,failover_pair_id=net1 + + failover_pair_id references the id of the virtio-net standby device. This + is only for pairing the devices within QEMU. The guest kernel module + net_failover will match devices with identical MAC addresses. + +Hotplug +------- + + Both primary and standby device can be hotplugged via the QEMU monitor. Note + that if the virtio-net device is plugged first a warning will be issued that it + couldn't find the primary device. + +Migration +--------- + + A new migration state wait-unplug was added for this feature. If failover primary + devices are present in the configuration, migration will go into this state. + It will wait until the device unplug is completed in the guest and then move into + active state. On the target system the primary devices will be automatically hotplugged + when the feature bit was negotiated for the virtio-net standby device. |