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 56Machine-specific options 57------------------------ 58 59The following machine-specific options are supported: 60 61- aclint=[on|off] 62 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". 65 66- aia=[none|aplic|aplic-imsic] 67 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. 75 76- aia-guests=nnn 77 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. 81 82Running Linux kernel 83-------------------- 84 85Linux mainline v5.12 release is tested at the time of writing. To build a 86Linux mainline kernel that can be booted by the ``virt`` machine in 8764-bit mode, simply configure the kernel using the defconfig configuration: 88 89.. code-block:: bash 90 91 $ export ARCH=riscv 92 $ export CROSS_COMPILE=riscv64-linux- 93 $ make defconfig 94 $ make 95 96To boot the newly built Linux kernel in QEMU with the ``virt`` machine: 97 98.. code-block:: bash 99 100 $ 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" 105 106To build a Linux mainline kernel that can be booted by the ``virt`` machine 107in 32-bit mode, use the rv32_defconfig configuration. A patch is required to 108fix the 32-bit boot issue for Linux kernel v5.12. 109 110.. code-block:: bash 111 112 $ export ARCH=riscv 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 115 $ git am riscv.patch 116 $ make rv32_defconfig 117 $ make 118 119Replace ``qemu-system-riscv64`` with ``qemu-system-riscv32`` in the command 120line above to boot the 32-bit Linux kernel. A rootfs image containing 32-bit 121applications shall be used in order for kernel to boot to user space. 122 123Running U-Boot 124-------------- 125 126U-Boot mainline v2021.04 release is tested at the time of writing. To build an 127S-mode U-Boot bootloader that can be booted by the ``virt`` machine, use 128the qemu-riscv64_smode_defconfig with similar commands as described above for Linux: 129 130.. code-block:: bash 131 132 $ export CROSS_COMPILE=riscv64-linux- 133 $ make qemu-riscv64_smode_defconfig 134 135Boot the 64-bit U-Boot S-mode image directly: 136 137.. code-block:: bash 138 139 $ qemu-system-riscv64 -M virt -smp 4 -m 2G \ 140 -display none -serial stdio \ 141 -kernel /path/to/u-boot.bin 142 143To test booting U-Boot SPL which in M-mode, which in turn loads a FIT image 144that bundles OpenSBI fw_dynamic firmware and U-Boot proper (S-mode) together, 145build the U-Boot images using riscv64_spl_defconfig: 146 147.. code-block:: bash 148 149 $ export CROSS_COMPILE=riscv64-linux- 150 $ export OPENSBI=/path/to/opensbi-riscv64-generic-fw_dynamic.bin 151 $ make qemu-riscv64_spl_defconfig 152 153The minimal QEMU commands to run U-Boot SPL are: 154 155.. code-block:: bash 156 157 $ 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 161 162To test 32-bit U-Boot images, switch to use qemu-riscv32_smode_defconfig and 163riscv32_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. 165 166Enabling TPM 167------------ 168 169A TPM device can be connected to the virt board by following the steps below. 170 171First launch the TPM emulator: 172 173.. code-block:: bash 174 175 $ swtpm socket --tpm2 -t -d --tpmstate dir=/tmp/tpm \ 176 --ctrl type=unixio,path=swtpm-sock 177 178Then launch QEMU with some additional arguments to link a TPM device to the backend: 179 180.. code-block:: bash 181 182 $ 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 187 188The TPM device can be seen in the memory tree and the generated device 189tree and should be accessible from the guest software. 190