1 'virt' generic virtual platform (``virt``)
2 ==========================================
4 The `virt` board is a platform which does not correspond to any
5 real hardware; it is designed for use in virtual machines.
6 It is the recommended board type if you simply want to run
7 a guest such as Linux and do not care about reproducing the
8 idiosyncrasies and limitations of a particular bit of real-world
11 This is a "versioned" board model, so as well as the ``virt`` machine
12 type itself (which may have improvements, bugfixes and other minor
13 changes between QEMU versions) a version is provided that guarantees
14 to have the same behaviour as that of previous QEMU releases, so
15 that VM migration will work between QEMU versions. For instance the
16 ``virt-5.0`` machine type will behave like the ``virt`` machine from
17 the QEMU 5.0 release, and migration should work between ``virt-5.0``
18 of the 5.0 release and ``virt-5.0`` of the 5.1 release. Migration
19 is not guaranteed to work between different QEMU releases for
20 the non-versioned ``virt`` machine type.
25 The virt board supports:
31 - The fw_cfg device that allows a guest to obtain data from QEMU
32 - A PL061 GPIO controller
33 - An optional SMMUv3 IOMMU
35 - hotpluggable NVDIMMs
36 - An MSI controller (GICv2M or ITS). GICv2M is selected by default along
37 with GICv2. ITS is selected by default with GICv3 (>= virt-2.7). Note
38 that ITS is not modeled in TCG mode.
39 - 32 virtio-mmio transport devices
40 - running guests using the KVM accelerator on aarch64 hardware
41 - large amounts of RAM (at least 255GB, and more if using highmem)
42 - many CPUs (up to 512 if using a GICv3 and highmem)
43 - Secure-World-only devices if the CPU has TrustZone:
46 - A second PL061 GPIO controller, with GPIO lines for triggering
47 a system reset or system poweroff
48 - A secure flash memory
51 Supported guest CPU types:
53 - ``cortex-a7`` (32-bit)
54 - ``cortex-a15`` (32-bit; the default)
55 - ``cortex-a53`` (64-bit)
56 - ``cortex-a57`` (64-bit)
57 - ``cortex-a72`` (64-bit)
58 - ``host`` (with KVM only)
59 - ``max`` (same as ``host`` for KVM; best possible emulation with TCG)
61 Note that the default is ``cortex-a15``, so for an AArch64 guest you must
64 Graphics output is available, but unlike the x86 PC machine types
65 there is no default display device enabled: you should select one from
66 the Display devices section of "-device help". The recommended option
67 is ``virtio-gpu-pci``; this is the only one which will work correctly
68 with KVM. You may also need to ensure your guest kernel is configured
69 with support for this; see below.
71 Machine-specific options
72 """"""""""""""""""""""""
74 The following machine-specific options are supported:
77 Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the
78 Arm Security Extensions (TrustZone). The default is ``off``.
81 Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the
82 Arm Virtualization Extensions. The default is ``off``.
85 Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the
86 Arm Memory Tagging Extensions. The default is ``off``.
89 Set ``on``/``off`` to enable/disable placing devices and RAM in physical
90 address space above 32 bits. The default is ``on`` for machine types
91 later than ``virt-2.12``.
94 Specify the version of the Generic Interrupt Controller (GIC) to provide.
102 Use the same GIC version the host provides, when using KVM
104 Use the best GIC version possible (same as host when using KVM;
105 currently same as ``3``` for TCG, but this may change in future)
108 Set ``on``/``off`` to enable/disable ITS instantiation. The default is ``on``
109 for machine types later than ``virt-2.7``.
112 Set the IOMMU type to create for the guest. Valid values are:
115 Don't create an IOMMU (the default)
120 Set ``on``/``off`` to enable/disable reporting host memory errors to a guest
121 using ACPI and guest external abort exceptions. The default is off.
123 Linux guest kernel configuration
124 """"""""""""""""""""""""""""""""
126 The 'defconfig' for Linux arm and arm64 kernels should include the
127 right device drivers for virtio and the PCI controller; however some older
128 kernel versions, especially for 32-bit Arm, did not have everything
129 enabled by default. If you're not seeing PCI devices that you expect,
130 then check that your guest config has::
134 CONFIG_PCI_HOST_GENERIC=y
136 If you want to use the ``virtio-gpu-pci`` graphics device you will also
140 CONFIG_DRM_VIRTIO_GPU=y
142 Hardware configuration information for bare-metal programming
143 """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
145 The ``virt`` board automatically generates a device tree blob ("dtb")
146 which it passes to the guest. This provides information about the
147 addresses, interrupt lines and other configuration of the various devices
148 in the system. Guest code can rely on and hard-code the following
151 - Flash memory starts at address 0x0000_0000
153 - RAM starts at 0x4000_0000
155 All other information about device locations may change between
156 QEMU versions, so guest code must look in the DTB.
158 QEMU supports two types of guest image boot for ``virt``, and
159 the way for the guest code to locate the dtb binary differs:
161 - For guests using the Linux kernel boot protocol (this means any
162 non-ELF file passed to the QEMU ``-kernel`` option) the address
163 of the DTB is passed in a register (``r2`` for 32-bit guests,
164 or ``x0`` for 64-bit guests)
166 - For guests booting as "bare-metal" (any other kind of boot),
167 the DTB is at the start of RAM (0x4000_0000)