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 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 51Supported guest CPU types: 52 53- ``cortex-a7`` (32-bit) 54- ``cortex-a15`` (32-bit; the default) 55- ``cortex-a35`` (64-bit) 56- ``cortex-a53`` (64-bit) 57- ``cortex-a55`` (64-bit) 58- ``cortex-a57`` (64-bit) 59- ``cortex-a72`` (64-bit) 60- ``cortex-a76`` (64-bit) 61- ``a64fx`` (64-bit) 62- ``host`` (with KVM only) 63- ``neoverse-n1`` (64-bit) 64- ``max`` (same as ``host`` for KVM; best possible emulation with TCG) 65 66Note that the default is ``cortex-a15``, so for an AArch64 guest you must 67specify a CPU type. 68 69Graphics output is available, but unlike the x86 PC machine types 70there is no default display device enabled: you should select one from 71the Display devices section of "-device help". The recommended option 72is ``virtio-gpu-pci``; this is the only one which will work correctly 73with KVM. You may also need to ensure your guest kernel is configured 74with support for this; see below. 75 76Machine-specific options 77"""""""""""""""""""""""" 78 79The following machine-specific options are supported: 80 81secure 82 Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the 83 Arm Security Extensions (TrustZone). The default is ``off``. 84 85virtualization 86 Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the 87 Arm Virtualization Extensions. The default is ``off``. 88 89mte 90 Set ``on``/``off`` to enable/disable emulating a guest CPU which implements the 91 Arm Memory Tagging Extensions. The default is ``off``. 92 93highmem 94 Set ``on``/``off`` to enable/disable placing devices and RAM in physical 95 address space above 32 bits. The default is ``on`` for machine types 96 later than ``virt-2.12``. 97 98compact-highmem 99 Set ``on``/``off`` to enable/disable the compact layout for high memory regions. 100 The default is ``on`` for machine types later than ``virt-7.2``. 101 102highmem-redists 103 Set ``on``/``off`` to enable/disable the high memory region for GICv3 or 104 GICv4 redistributor. The default is ``on``. Setting this to ``off`` will 105 limit the maximum number of CPUs when GICv3 or GICv4 is used. 106 107highmem-ecam 108 Set ``on``/``off`` to enable/disable the high memory region for PCI ECAM. 109 The default is ``on`` for machine types later than ``virt-3.0``. 110 111highmem-mmio 112 Set ``on``/``off`` to enable/disable the high memory region for PCI MMIO. 113 The default is ``on``. 114 115gic-version 116 Specify the version of the Generic Interrupt Controller (GIC) to provide. 117 Valid values are: 118 119 ``2`` 120 GICv2. Note that this limits the number of CPUs to 8. 121 ``3`` 122 GICv3. This allows up to 512 CPUs. 123 ``4`` 124 GICv4. Requires ``virtualization`` to be ``on``; allows up to 317 CPUs. 125 ``host`` 126 Use the same GIC version the host provides, when using KVM 127 ``max`` 128 Use the best GIC version possible (same as host when using KVM; 129 with TCG this is currently ``3`` if ``virtualization`` is ``off`` and 130 ``4`` if ``virtualization`` is ``on``, but this may change in future) 131 132its 133 Set ``on``/``off`` to enable/disable ITS instantiation. The default is ``on`` 134 for machine types later than ``virt-2.7``. 135 136iommu 137 Set the IOMMU type to create for the guest. Valid values are: 138 139 ``none`` 140 Don't create an IOMMU (the default) 141 ``smmuv3`` 142 Create an SMMUv3 143 144ras 145 Set ``on``/``off`` to enable/disable reporting host memory errors to a guest 146 using ACPI and guest external abort exceptions. The default is off. 147 148dtb-randomness 149 Set ``on``/``off`` to pass random seeds via the guest DTB 150 rng-seed and kaslr-seed nodes (in both "/chosen" and 151 "/secure-chosen") to use for features like the random number 152 generator and address space randomisation. The default is 153 ``on``. You will want to disable it if your trusted boot chain 154 will verify the DTB it is passed, since this option causes the 155 DTB to be non-deterministic. It would be the responsibility of 156 the firmware to come up with a seed and pass it on if it wants to. 157 158dtb-kaslr-seed 159 A deprecated synonym for dtb-randomness. 160 161Linux guest kernel configuration 162"""""""""""""""""""""""""""""""" 163 164The 'defconfig' for Linux arm and arm64 kernels should include the 165right device drivers for virtio and the PCI controller; however some older 166kernel versions, especially for 32-bit Arm, did not have everything 167enabled by default. If you're not seeing PCI devices that you expect, 168then check that your guest config has:: 169 170 CONFIG_PCI=y 171 CONFIG_VIRTIO_PCI=y 172 CONFIG_PCI_HOST_GENERIC=y 173 174If you want to use the ``virtio-gpu-pci`` graphics device you will also 175need:: 176 177 CONFIG_DRM=y 178 CONFIG_DRM_VIRTIO_GPU=y 179 180Hardware configuration information for bare-metal programming 181""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 182 183The ``virt`` board automatically generates a device tree blob ("dtb") 184which it passes to the guest. This provides information about the 185addresses, interrupt lines and other configuration of the various devices 186in the system. Guest code can rely on and hard-code the following 187addresses: 188 189- Flash memory starts at address 0x0000_0000 190 191- RAM starts at 0x4000_0000 192 193All other information about device locations may change between 194QEMU versions, so guest code must look in the DTB. 195 196QEMU supports two types of guest image boot for ``virt``, and 197the way for the guest code to locate the dtb binary differs: 198 199- For guests using the Linux kernel boot protocol (this means any 200 non-ELF file passed to the QEMU ``-kernel`` option) the address 201 of the DTB is passed in a register (``r2`` for 32-bit guests, 202 or ``x0`` for 64-bit guests) 203 204- For guests booting as "bare-metal" (any other kind of boot), 205 the DTB is at the start of RAM (0x4000_0000) 206