docs/system/arm/virt.rst

   1 'virt' generic virtual platform (``virt``)
   2 ==========================================
   3
   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
   9 hardware.
  10
  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.
  21
  22 Supported devices
  23 """""""""""""""""
  24
  25 The virt board supports:
  26
  27 - PCI/PCIe devices
  28 - Flash memory
  29 - One PL011 UART
  30 - An RTC
  31 - The fw_cfg device that allows a guest to obtain data from QEMU
  32 - A PL061 GPIO controller
  33 - An optional SMMUv3 IOMMU
  34 - hotpluggable DIMMs
  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:
  44
  45   - A second PL011 UART
  46   - A second PL061 GPIO controller, with GPIO lines for triggering
  47     a system reset or system poweroff
  48   - A secure flash memory
  49   - 16MB of secure RAM
  50
  51 Supported guest CPU types:
  52
  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 - ``a64fx`` (64-bit)
  59 - ``host`` (with KVM only)
  60 - ``max`` (same as ``host`` for KVM; best possible emulation with TCG)
  61
  62 Note that the default is ``cortex-a15``, so for an AArch64 guest you must
  63 specify a CPU type.
  64
  65 Graphics output is available, but unlike the x86 PC machine types
  66 there is no default display device enabled: you should select one from
  67 the Display devices section of "-device help". The recommended option
  68 is ``virtio-gpu-pci``; this is the only one which will work correctly
  69 with KVM. You may also need to ensure your guest kernel is configured
  70 with support for this; see below.
  71
  72 Machine-specific options
  73 """"""""""""""""""""""""
  74
  75 The following machine-specific options are supported:
  76
  77 secure
  78   Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the
  79   Arm Security Extensions (TrustZone). The default is ``off``.
  80
  81 virtualization
  82   Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the
  83   Arm Virtualization Extensions. The default is ``off``.
  84
  85 mte
  86   Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the
  87   Arm Memory Tagging Extensions. The default is ``off``.
  88
  89 highmem
  90   Set ``on``/``off`` to enable/disable placing devices and RAM in physical
  91   address space above 32 bits. The default is ``on`` for machine types
  92   later than ``virt-2.12``.
  93
  94 gic-version
  95   Specify the version of the Generic Interrupt Controller (GIC) to provide.
  96   Valid values are:
  97
  98   ``2``
  99     GICv2. Note that this limits the number of CPUs to 8.
 100   ``3``
 101     GICv3. This allows up to 512 CPUs.
 102   ``4``
 103     GICv4. Requires ``virtualization`` to be ``on``; allows up to 317 CPUs.
 104   ``host``
 105     Use the same GIC version the host provides, when using KVM
 106   ``max``
 107     Use the best GIC version possible (same as host when using KVM;
 108     with TCG this is currently ``3`` if ``virtualization`` is ``off`` and
 109     ``4`` if ``virtualization`` is ``on``, but this may change in future)
 110
 111 its
 112   Set ``on``/``off`` to enable/disable ITS instantiation. The default is ``on``
 113   for machine types later than ``virt-2.7``.
 114
 115 iommu
 116   Set the IOMMU type to create for the guest. Valid values are:
 117
 118   ``none``
 119     Don't create an IOMMU (the default)
 120   ``smmuv3``
 121     Create an SMMUv3
 122
 123 ras
 124   Set ``on``/``off`` to enable/disable reporting host memory errors to a guest
 125   using ACPI and guest external abort exceptions. The default is off.
 126
 127 dtb-kaslr-seed
 128   Set ``on``/``off`` to pass a random seed via the guest dtb
 129   kaslr-seed node (in both "/chosen" and /secure-chosen) to use
 130   for features like address space randomisation. The default is
 131   ``on``. You will want to disable it if your trusted boot chain will
 132   verify the DTB it is passed. It would be the responsibility of the
 133   firmware to come up with a seed and pass it on if it wants to.
 134
 135 Linux guest kernel configuration
 136 """"""""""""""""""""""""""""""""
 137
 138 The 'defconfig' for Linux arm and arm64 kernels should include the
 139 right device drivers for virtio and the PCI controller; however some older
 140 kernel versions, especially for 32-bit Arm, did not have everything
 141 enabled by default. If you're not seeing PCI devices that you expect,
 142 then check that your guest config has::
 143
 144   CONFIG_PCI=y
 145   CONFIG_VIRTIO_PCI=y
 146   CONFIG_PCI_HOST_GENERIC=y
 147
 148 If you want to use the ``virtio-gpu-pci`` graphics device you will also
 149 need::
 150
 151   CONFIG_DRM=y
 152   CONFIG_DRM_VIRTIO_GPU=y
 153
 154 Hardware configuration information for bare-metal programming
 155 """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
 156
 157 The ``virt`` board automatically generates a device tree blob ("dtb")
 158 which it passes to the guest. This provides information about the
 159 addresses, interrupt lines and other configuration of the various devices
 160 in the system. Guest code can rely on and hard-code the following
 161 addresses:
 162
 163 - Flash memory starts at address 0x0000_0000
 164
 165 - RAM starts at 0x4000_0000
 166
 167 All other information about device locations may change between
 168 QEMU versions, so guest code must look in the DTB.
 169
 170 QEMU supports two types of guest image boot for ``virt``, and
 171 the way for the guest code to locate the dtb binary differs:
 172
 173 - For guests using the Linux kernel boot protocol (this means any
 174   non-ELF file passed to the QEMU ``-kernel`` option) the address
 175   of the DTB is passed in a register (``r2`` for 32-bit guests,
 176   or ``x0`` for 64-bit guests)
 177
 178 - For guests booting as "bare-metal" (any other kind of boot),
 179   the DTB is at the start of RAM (0x4000_0000)