RISC-V: Executing floating point instruction in VS mode under KVM acceleration leads to crash

Host environment

• Operating system: Ubuntu 24.10
• OS/kernel version: 6.11-rc7
• Architecture: riscv64
• QEMU flavor: qemu-system-riscv64
• QEMU version: 9.0.2+ds-4ubuntu5
• QEMU command line:

  • outer VM

    qemu-system-riscv64 \
    -machine virt -nographic -m 4096 -smp 4 \
    -bios /usr/lib/riscv64-linux-gnu/opensbi/generic/fw_jump.bin \
    -kernel /usr/lib/u-boot/qemu-riscv64_smode/uboot.elf \
    -device virtio-net-device,netdev=eth0 -netdev user,id=eth0 \
    -device virtio-rng-pci \
    -drive file=ubuntu-24.04-preinstalled-server-riscv64.img,format=raw,if=virtio

  • inner VM

    qemu-system-riscv64 \
    -machine virt -nographic -m 2048 -smp 4 -accel kvm \
    -kernel payload.bin

Emulated/Virtualized environment

• Payload: https://github.com/xypron/riscv_test_payload/blob/fa666634c3eeca583895bea78ea730e94bca1208/payload.S
• Architecture: riscv64

Description of problem

Executing fcvt.d.w fa5,a5 in VS mode leads to crash.

Steps to reproduce

1. Download the Ubuntu 24.10 image https://cdimage.ubuntu.com/ubuntu-server/daily-preinstalled/current/oracular-preinstalled-server-riscv64.img.xz
2. On your amd64 system launch a VM using -accel tcg
3. Inside the VM launch a new VM using -accel kvm with the payload mentioned above

Additional information

For more details see https://bugs.launchpad.net/ubuntu/+source/edk2/+bug/2077731