1 'virt' Generic Virtual Platform (``virt``)
2 ==========================================
4 The ``virt`` board is a platform which does not correspond to any real hardware;
5 it is designed for use in virtual machines. It is the recommended board type
6 if you simply want to run a guest such as Linux and do not care about
7 reproducing the idiosyncrasies and limitations of a particular bit of
13 The ``virt`` machine supports the following devices:
15 * Up to 8 generic RV32GC/RV64GC cores, with optional extensions
16 * Core Local Interruptor (CLINT)
17 * Platform-Level Interrupt Controller (PLIC)
18 * CFI parallel NOR flash memory
19 * 1 NS16550 compatible UART
20 * 1 Google Goldfish RTC
21 * 1 SiFive Test device
22 * 8 virtio-mmio transport devices
23 * 1 generic PCIe host bridge
24 * The fw_cfg device that allows a guest to obtain data from QEMU
26 The hypervisor extension has been enabled for the default CPU, so virtual
27 machines with hypervisor extension can simply be used without explicitly
30 Hardware configuration information
31 ----------------------------------
33 The ``virt`` machine automatically generates a device tree blob ("dtb")
34 which it passes to the guest, if there is no ``-dtb`` option. This provides
35 information about the addresses, interrupt lines and other configuration of
36 the various devices in the system. Guest software should discover the devices
37 that are present in the generated DTB.
39 If users want to provide their own DTB, they can use the ``-dtb`` option.
40 These DTBs should have the following requirements:
42 * The number of subnodes of the /cpus node should match QEMU's ``-smp`` option
43 * The /memory reg size should match QEMU’s selected ram_size via ``-m``
44 * Should contain a node for the CLINT device with a compatible string
45 "riscv,clint0" if using with OpenSBI BIOS images
50 The ``virt`` machine can start using the standard -kernel functionality
51 for loading a Linux kernel, a VxWorks kernel, an S-mode U-Boot bootloader
52 with the default OpenSBI firmware image as the -bios. It also supports
53 the recommended RISC-V bootflow: U-Boot SPL (M-mode) loads OpenSBI fw_dynamic
54 firmware and U-Boot proper (S-mode), using the standard -bios functionality.
56 Machine-specific options
57 ------------------------
59 The following machine-specific options are supported:
63 When this option is "on", ACLINT devices will be emulated instead of
64 SiFive CLINT. When not specified, this option is assumed to be "off".
66 - aia=[none|aplic|aplic-imsic]
68 This option allows selecting interrupt controller defined by the AIA
69 (advanced interrupt architecture) specification. The "aia=aplic" selects
70 APLIC (advanced platform level interrupt controller) to handle wired
71 interrupts whereas the "aia=aplic-imsic" selects APLIC and IMSIC (incoming
72 message signaled interrupt controller) to handle both wired interrupts and
73 MSIs. When not specified, this option is assumed to be "none" which selects
74 SiFive PLIC to handle wired interrupts.
78 The number of per-HART VS-level AIA IMSIC pages to be emulated for a guest
79 having AIA IMSIC (i.e. "aia=aplic-imsic" selected). When not specified,
80 the default number of per-HART VS-level AIA IMSIC pages is 0.
85 Linux mainline v5.12 release is tested at the time of writing. To build a
86 Linux mainline kernel that can be booted by the ``virt`` machine in
87 64-bit mode, simply configure the kernel using the defconfig configuration:
92 $ export CROSS_COMPILE=riscv64-linux-
96 To boot the newly built Linux kernel in QEMU with the ``virt`` machine:
100 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \
101 -display none -serial stdio \
102 -kernel arch/riscv/boot/Image \
103 -initrd /path/to/rootfs.cpio \
104 -append "root=/dev/ram"
106 To build a Linux mainline kernel that can be booted by the ``virt`` machine
107 in 32-bit mode, use the rv32_defconfig configuration. A patch is required to
108 fix the 32-bit boot issue for Linux kernel v5.12.
113 $ export CROSS_COMPILE=riscv64-linux-
114 $ curl https://patchwork.kernel.org/project/linux-riscv/patch/20210627135117.28641-1-bmeng.cn@gmail.com/mbox/ > riscv.patch
116 $ make rv32_defconfig
119 Replace ``qemu-system-riscv64`` with ``qemu-system-riscv32`` in the command
120 line above to boot the 32-bit Linux kernel. A rootfs image containing 32-bit
121 applications shall be used in order for kernel to boot to user space.
126 U-Boot mainline v2021.04 release is tested at the time of writing. To build an
127 S-mode U-Boot bootloader that can be booted by the ``virt`` machine, use
128 the qemu-riscv64_smode_defconfig with similar commands as described above for Linux:
132 $ export CROSS_COMPILE=riscv64-linux-
133 $ make qemu-riscv64_smode_defconfig
135 Boot the 64-bit U-Boot S-mode image directly:
139 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \
140 -display none -serial stdio \
141 -kernel /path/to/u-boot.bin
143 To test booting U-Boot SPL which in M-mode, which in turn loads a FIT image
144 that bundles OpenSBI fw_dynamic firmware and U-Boot proper (S-mode) together,
145 build the U-Boot images using riscv64_spl_defconfig:
149 $ export CROSS_COMPILE=riscv64-linux-
150 $ export OPENSBI=/path/to/opensbi-riscv64-generic-fw_dynamic.bin
151 $ make qemu-riscv64_spl_defconfig
153 The minimal QEMU commands to run U-Boot SPL are:
157 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \
158 -display none -serial stdio \
159 -bios /path/to/u-boot-spl \
160 -device loader,file=/path/to/u-boot.itb,addr=0x80200000
162 To test 32-bit U-Boot images, switch to use qemu-riscv32_smode_defconfig and
163 riscv32_spl_defconfig builds, and replace ``qemu-system-riscv64`` with
164 ``qemu-system-riscv32`` in the command lines above to boot the 32-bit U-Boot.
169 A TPM device can be connected to the virt board by following the steps below.
171 First launch the TPM emulator:
175 $ swtpm socket --tpm2 -t -d --tpmstate dir=/tmp/tpm \
176 --ctrl type=unixio,path=swtpm-sock
178 Then launch QEMU with some additional arguments to link a TPM device to the backend:
182 $ qemu-system-riscv64 \
183 ... other args .... \
184 -chardev socket,id=chrtpm,path=swtpm-sock \
185 -tpmdev emulator,id=tpm0,chardev=chrtpm \
186 -device tpm-tis-device,tpmdev=tpm0
188 The TPM device can be seen in the memory tree and the generated device
189 tree and should be accessible from the guest software.