1'virt' generic virtual platform (``virt``) 2========================================== 3 4The `virt` board is a platform which does not correspond to any 5real hardware; it is designed for use in virtual machines. 6It is the recommended board type if you simply want to run 7a guest such as Linux and do not care about reproducing the 8idiosyncrasies and limitations of a particular bit of real-world 9hardware. 10 11This is a "versioned" board model, so as well as the ``virt`` machine 12type itself (which may have improvements, bugfixes and other minor 13changes between QEMU versions) a version is provided that guarantees 14to have the same behaviour as that of previous QEMU releases, so 15that VM migration will work between QEMU versions. For instance the 16``virt-5.0`` machine type will behave like the ``virt`` machine from 17the QEMU 5.0 release, and migration should work between ``virt-5.0`` 18of the 5.0 release and ``virt-5.0`` of the 5.1 release. Migration 19is not guaranteed to work between different QEMU releases for 20the non-versioned ``virt`` machine type. 21 22Supported devices 23""""""""""""""""" 24 25The 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 secure flash memory 47 - 16MB of secure RAM 48 49Supported guest CPU types: 50 51- ``cortex-a7`` (32-bit) 52- ``cortex-a15`` (32-bit; the default) 53- ``cortex-a53`` (64-bit) 54- ``cortex-a57`` (64-bit) 55- ``cortex-a72`` (64-bit) 56- ``host`` (with KVM only) 57- ``max`` (same as ``host`` for KVM; best possible emulation with TCG) 58 59Note that the default is ``cortex-a15``, so for an AArch64 guest you must 60specify a CPU type. 61 62Graphics output is available, but unlike the x86 PC machine types 63there is no default display device enabled: you should select one from 64the Display devices section of "-device help". The recommended option 65is ``virtio-gpu-pci``; this is the only one which will work correctly 66with KVM. You may also need to ensure your guest kernel is configured 67with support for this; see below. 68 69Machine-specific options 70"""""""""""""""""""""""" 71 72The following machine-specific options are supported: 73 74secure 75 Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the 76 Arm Security Extensions (TrustZone). The default is ``off``. 77 78virtualization 79 Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the 80 Arm Virtualization Extensions. The default is ``off``. 81 82mte 83 Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the 84 Arm Memory Tagging Extensions. The default is ``off``. 85 86highmem 87 Set ``on``/``off`` to enable/disable placing devices and RAM in physical 88 address space above 32 bits. The default is ``on`` for machine types 89 later than ``virt-2.12``. 90 91gic-version 92 Specify the version of the Generic Interrupt Controller (GIC) to provide. 93 Valid values are: 94 95 ``2`` 96 GICv2 97 ``3`` 98 GICv3 99 ``host`` 100 Use the same GIC version the host provides, when using KVM 101 ``max`` 102 Use the best GIC version possible (same as host when using KVM; 103 currently same as ``3``` for TCG, but this may change in future) 104 105its 106 Set ``on``/``off`` to enable/disable ITS instantiation. The default is ``on`` 107 for machine types later than ``virt-2.7``. 108 109iommu 110 Set the IOMMU type to create for the guest. Valid values are: 111 112 ``none`` 113 Don't create an IOMMU (the default) 114 ``smmuv3`` 115 Create an SMMUv3 116 117ras 118 Set ``on``/``off`` to enable/disable reporting host memory errors to a guest 119 using ACPI and guest external abort exceptions. The default is off. 120 121Linux guest kernel configuration 122"""""""""""""""""""""""""""""""" 123 124The 'defconfig' for Linux arm and arm64 kernels should include the 125right device drivers for virtio and the PCI controller; however some older 126kernel versions, especially for 32-bit Arm, did not have everything 127enabled by default. If you're not seeing PCI devices that you expect, 128then check that your guest config has:: 129 130 CONFIG_PCI=y 131 CONFIG_VIRTIO_PCI=y 132 CONFIG_PCI_HOST_GENERIC=y 133 134If you want to use the ``virtio-gpu-pci`` graphics device you will also 135need:: 136 137 CONFIG_DRM=y 138 CONFIG_DRM_VIRTIO_GPU=y 139 140Hardware configuration information for bare-metal programming 141""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 142 143The ``virt`` board automatically generates a device tree blob ("dtb") 144which it passes to the guest. This provides information about the 145addresses, interrupt lines and other configuration of the various devices 146in the system. Guest code can rely on and hard-code the following 147addresses: 148 149- Flash memory starts at address 0x0000_0000 150 151- RAM starts at 0x4000_0000 152 153All other information about device locations may change between 154QEMU versions, so guest code must look in the DTB. 155 156QEMU supports two types of guest image boot for ``virt``, and 157the way for the guest code to locate the dtb binary differs: 158 159- For guests using the Linux kernel boot protocol (this means any 160 non-ELF file passed to the QEMU ``-kernel`` option) the address 161 of the DTB is passed in a register (``r2`` for 32-bit guests, 162 or ``x0`` for 64-bit guests) 163 164- For guests booting as "bare-metal" (any other kind of boot), 165 the DTB is at the start of RAM (0x4000_0000) 166