1'virt' Generic Virtual Platform (``virt``) 2========================================== 3 4The ``virt`` board is a platform which does not correspond to any real hardware; 5it is designed for use in virtual machines. It is the recommended board type 6if you simply want to run a guest such as Linux and do not care about 7reproducing the idiosyncrasies and limitations of a particular bit of 8real-world hardware. 9 10Supported devices 11----------------- 12 13The ``virt`` machine supports the following devices: 14 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 25 26The hypervisor extension has been enabled for the default CPU, so virtual 27machines with hypervisor extension can simply be used without explicitly 28declaring. 29 30Hardware configuration information 31---------------------------------- 32 33The ``virt`` machine automatically generates a device tree blob ("dtb") 34which it passes to the guest, if there is no ``-dtb`` option. This provides 35information about the addresses, interrupt lines and other configuration of 36the various devices in the system. Guest software should discover the devices 37that are present in the generated DTB. 38 39If users want to provide their own DTB, they can use the ``-dtb`` option. 40These DTBs should have the following requirements: 41 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 46 47Boot options 48------------ 49 50The ``virt`` machine can start using the standard -kernel functionality 51for loading a Linux kernel, a VxWorks kernel, an S-mode U-Boot bootloader 52with the default OpenSBI firmware image as the -bios. It also supports 53the recommended RISC-V bootflow: U-Boot SPL (M-mode) loads OpenSBI fw_dynamic 54firmware and U-Boot proper (S-mode), using the standard -bios functionality. 55 56Using flash devices 57------------------- 58 59By default, the first flash device (pflash0) is expected to contain 60S-mode firmware code. It can be configured as read-only, with the 61second flash device (pflash1) available to store configuration data. 62 63For example, booting edk2 looks like 64 65.. code-block:: bash 66 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 \ 71 ... other args .... 72 73For TCG guests only, it is also possible to boot M-mode firmware from 74the first flash device (pflash0) by additionally passing ``-bios 75none``, as in 76 77.. code-block:: bash 78 79 $ qemu-system-riscv64 \ 80 -bios none \ 81 -blockdev node-name=pflash0,driver=file,read-only=on,filename=<m_mode_code> \ 82 -M virt,pflash0=pflash0 \ 83 ... other args .... 84 85Firmware images used for pflash must be exactly 32 MiB in size. 86 87Machine-specific options 88------------------------ 89 90The following machine-specific options are supported: 91 92- aclint=[on|off] 93 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 97- aia=[none|aplic|aplic-imsic] 98 99 This option allows selecting interrupt controller defined by the AIA 100 (advanced interrupt architecture) specification. The "aia=aplic" selects 101 APLIC (advanced platform level interrupt controller) to handle wired 102 interrupts whereas the "aia=aplic-imsic" selects APLIC and IMSIC (incoming 103 message signaled interrupt controller) to handle both wired interrupts and 104 MSIs. When not specified, this option is assumed to be "none" which selects 105 SiFive PLIC to handle wired interrupts. 106 107- aia-guests=nnn 108 109 The number of per-HART VS-level AIA IMSIC pages to be emulated for a guest 110 having AIA IMSIC (i.e. "aia=aplic-imsic" selected). When not specified, 111 the default number of per-HART VS-level AIA IMSIC pages is 0. 112 113Running Linux kernel 114-------------------- 115 116Linux mainline v5.12 release is tested at the time of writing. To build a 117Linux mainline kernel that can be booted by the ``virt`` machine in 11864-bit mode, simply configure the kernel using the defconfig configuration: 119 120.. code-block:: bash 121 122 $ export ARCH=riscv 123 $ export CROSS_COMPILE=riscv64-linux- 124 $ make defconfig 125 $ make 126 127To boot the newly built Linux kernel in QEMU with the ``virt`` machine: 128 129.. code-block:: bash 130 131 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \ 132 -display none -serial stdio \ 133 -kernel arch/riscv/boot/Image \ 134 -initrd /path/to/rootfs.cpio \ 135 -append "root=/dev/ram" 136 137To build a Linux mainline kernel that can be booted by the ``virt`` machine 138in 32-bit mode, use the rv32_defconfig configuration. A patch is required to 139fix the 32-bit boot issue for Linux kernel v5.12. 140 141.. code-block:: bash 142 143 $ export ARCH=riscv 144 $ export CROSS_COMPILE=riscv64-linux- 145 $ curl https://patchwork.kernel.org/project/linux-riscv/patch/20210627135117.28641-1-bmeng.cn@gmail.com/mbox/ > riscv.patch 146 $ git am riscv.patch 147 $ make rv32_defconfig 148 $ make 149 150Replace ``qemu-system-riscv64`` with ``qemu-system-riscv32`` in the command 151line above to boot the 32-bit Linux kernel. A rootfs image containing 32-bit 152applications shall be used in order for kernel to boot to user space. 153 154Running U-Boot 155-------------- 156 157U-Boot mainline v2021.04 release is tested at the time of writing. To build an 158S-mode U-Boot bootloader that can be booted by the ``virt`` machine, use 159the qemu-riscv64_smode_defconfig with similar commands as described above for Linux: 160 161.. code-block:: bash 162 163 $ export CROSS_COMPILE=riscv64-linux- 164 $ make qemu-riscv64_smode_defconfig 165 166Boot the 64-bit U-Boot S-mode image directly: 167 168.. code-block:: bash 169 170 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \ 171 -display none -serial stdio \ 172 -kernel /path/to/u-boot.bin 173 174To test booting U-Boot SPL which in M-mode, which in turn loads a FIT image 175that bundles OpenSBI fw_dynamic firmware and U-Boot proper (S-mode) together, 176build the U-Boot images using riscv64_spl_defconfig: 177 178.. code-block:: bash 179 180 $ export CROSS_COMPILE=riscv64-linux- 181 $ export OPENSBI=/path/to/opensbi-riscv64-generic-fw_dynamic.bin 182 $ make qemu-riscv64_spl_defconfig 183 184The minimal QEMU commands to run U-Boot SPL are: 185 186.. code-block:: bash 187 188 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \ 189 -display none -serial stdio \ 190 -bios /path/to/u-boot-spl \ 191 -device loader,file=/path/to/u-boot.itb,addr=0x80200000 192 193To test 32-bit U-Boot images, switch to use qemu-riscv32_smode_defconfig and 194riscv32_spl_defconfig builds, and replace ``qemu-system-riscv64`` with 195``qemu-system-riscv32`` in the command lines above to boot the 32-bit U-Boot. 196 197Enabling TPM 198------------ 199 200A TPM device can be connected to the virt board by following the steps below. 201 202First launch the TPM emulator: 203 204.. code-block:: bash 205 206 $ swtpm socket --tpm2 -t -d --tpmstate dir=/tmp/tpm \ 207 --ctrl type=unixio,path=swtpm-sock 208 209Then launch QEMU with some additional arguments to link a TPM device to the backend: 210 211.. code-block:: bash 212 213 $ qemu-system-riscv64 \ 214 ... other args .... \ 215 -chardev socket,id=chrtpm,path=swtpm-sock \ 216 -tpmdev emulator,id=tpm0,chardev=chrtpm \ 217 -device tpm-tis-device,tpmdev=tpm0 218 219The TPM device can be seen in the memory tree and the generated device 220tree and should be accessible from the guest software. 221