docs/system/riscv/virt.rst

   1 'virt' Generic Virtual Platform (``virt``)
   2 ==========================================
   3
   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
   8 real-world hardware.
   9
  10 Supported devices
  11 -----------------
  12
  13 The ``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
  26 The hypervisor extension has been enabled for the default CPU, so virtual
  27 machines with hypervisor extension can simply be used without explicitly
  28 declaring.
  29
  30 Hardware configuration information
  31 ----------------------------------
  32
  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.
  38
  39 If users want to provide their own DTB, they can use the ``-dtb`` option.
  40 These 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
  47 Boot options
  48 ------------
  49
  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.
  55
  56 Machine-specific options
  57 ------------------------
  58
  59 The 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
  82 Running Linux kernel
  83 --------------------
  84
  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:
  88
  89 .. code-block:: bash
  90
  91   $ export ARCH=riscv
  92   $ export CROSS_COMPILE=riscv64-linux-
  93   $ make defconfig
  94   $ make
  95
  96 To 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
 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.
 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
 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.
 122
 123 Running U-Boot
 124 --------------
 125
 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:
 129
 130 .. code-block:: bash
 131
 132   $ export CROSS_COMPILE=riscv64-linux-
 133   $ make qemu-riscv64_smode_defconfig
 134
 135 Boot 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
 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:
 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
 153 The 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
 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.
 165
 166 Enabling TPM
 167 ------------
 168
 169 A TPM device can be connected to the virt board by following the steps below.
 170
 171 First 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
 178 Then 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
 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.