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 512 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.
59 By default, the first flash device (pflash0) is expected to contain
60 S-mode firmware code. It can be configured as read-only, with the
61 second flash device (pflash1) available to store configuration data.
63 For example, booting edk2 looks like
67 $ qemu-system-riscv64 \
68 -blockdev node-name=pflash0,driver=file,read-only=on,filename=<edk2_code> \
69 -blockdev node-name=pflash1,driver=file,filename=<edk2_vars> \
70 -M virt,pflash0=pflash0,pflash1=pflash1 \
73 For TCG guests only, it is also possible to boot M-mode firmware from
74 the first flash device (pflash0) by additionally passing ``-bios
79 $ qemu-system-riscv64 \
81 -blockdev node-name=pflash0,driver=file,read-only=on,filename=<m_mode_code> \
82 -M virt,pflash0=pflash0 \
85 Firmware images used for pflash must be exactly 32 MiB in size.
87 Machine-specific options
88 ------------------------
90 The following machine-specific options are supported:
94 When this option is "on", ACLINT devices will be emulated instead of
95 SiFive CLINT. When not specified, this option is assumed to be "off".
96 This option is restricted to the TCG accelerator.
98 - aia=[none|aplic|aplic-imsic]
100 This option allows selecting interrupt controller defined by the AIA
101 (advanced interrupt architecture) specification. The "aia=aplic" selects
102 APLIC (advanced platform level interrupt controller) to handle wired
103 interrupts whereas the "aia=aplic-imsic" selects APLIC and IMSIC (incoming
104 message signaled interrupt controller) to handle both wired interrupts and
105 MSIs. When not specified, this option is assumed to be "none" which selects
106 SiFive PLIC to handle wired interrupts.
110 The number of per-HART VS-level AIA IMSIC pages to be emulated for a guest
111 having AIA IMSIC (i.e. "aia=aplic-imsic" selected). When not specified,
112 the default number of per-HART VS-level AIA IMSIC pages is 0.
117 Linux mainline v5.12 release is tested at the time of writing. To build a
118 Linux mainline kernel that can be booted by the ``virt`` machine in
119 64-bit mode, simply configure the kernel using the defconfig configuration:
124 $ export CROSS_COMPILE=riscv64-linux-
128 To boot the newly built Linux kernel in QEMU with the ``virt`` machine:
132 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \
133 -display none -serial stdio \
134 -kernel arch/riscv/boot/Image \
135 -initrd /path/to/rootfs.cpio \
136 -append "root=/dev/ram"
138 To build a Linux mainline kernel that can be booted by the ``virt`` machine
139 in 32-bit mode, use the rv32_defconfig configuration. A patch is required to
140 fix the 32-bit boot issue for Linux kernel v5.12.
145 $ export CROSS_COMPILE=riscv64-linux-
146 $ curl https://patchwork.kernel.org/project/linux-riscv/patch/20210627135117.28641-1-bmeng.cn@gmail.com/mbox/ > riscv.patch
148 $ make rv32_defconfig
151 Replace ``qemu-system-riscv64`` with ``qemu-system-riscv32`` in the command
152 line above to boot the 32-bit Linux kernel. A rootfs image containing 32-bit
153 applications shall be used in order for kernel to boot to user space.
158 U-Boot mainline v2021.04 release is tested at the time of writing. To build an
159 S-mode U-Boot bootloader that can be booted by the ``virt`` machine, use
160 the qemu-riscv64_smode_defconfig with similar commands as described above for Linux:
164 $ export CROSS_COMPILE=riscv64-linux-
165 $ make qemu-riscv64_smode_defconfig
167 Boot the 64-bit U-Boot S-mode image directly:
171 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \
172 -display none -serial stdio \
173 -kernel /path/to/u-boot.bin
175 To test booting U-Boot SPL which in M-mode, which in turn loads a FIT image
176 that bundles OpenSBI fw_dynamic firmware and U-Boot proper (S-mode) together,
177 build the U-Boot images using riscv64_spl_defconfig:
181 $ export CROSS_COMPILE=riscv64-linux-
182 $ export OPENSBI=/path/to/opensbi-riscv64-generic-fw_dynamic.bin
183 $ make qemu-riscv64_spl_defconfig
185 The minimal QEMU commands to run U-Boot SPL are:
189 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \
190 -display none -serial stdio \
191 -bios /path/to/u-boot-spl \
192 -device loader,file=/path/to/u-boot.itb,addr=0x80200000
194 To test 32-bit U-Boot images, switch to use qemu-riscv32_smode_defconfig and
195 riscv32_spl_defconfig builds, and replace ``qemu-system-riscv64`` with
196 ``qemu-system-riscv32`` in the command lines above to boot the 32-bit U-Boot.
201 A TPM device can be connected to the virt board by following the steps below.
203 First launch the TPM emulator:
207 $ swtpm socket --tpm2 -t -d --tpmstate dir=/tmp/tpm \
208 --ctrl type=unixio,path=swtpm-sock
210 Then launch QEMU with some additional arguments to link a TPM device to the backend:
214 $ qemu-system-riscv64 \
215 ... other args .... \
216 -chardev socket,id=chrtpm,path=swtpm-sock \
217 -tpmdev emulator,id=tpm0,chardev=chrtpm \
218 -device tpm-tis-device,tpmdev=tpm0
220 The TPM device can be seen in the memory tree and the generated device
221 tree and should be accessible from the guest software.