qemu-system-loongarch64 failed to run with kvm accel on Loongarch host with kernel 6.6

Host environment

  • Operating system:

    Debian sid

  • OS/kernel version:

    Linux debian 6.6.52-loong64 #1 SMP Debian 6.6.52-1.4 (2025-05-14) loongarch64 GNU/Linux

  • Architecture:

    Loongarch64

  • QEMU flavor:

    qemu-system-loongarch64

  • QEMU version:

    QEMU emulator version 10.1.0 (Debian 1:10.1.0+ds-5)

  • QEMU command line:

    qemu-system-loongarch64 \
    -m 4G \
    -cpu la464-loongarch-cpu \
    -machine virt \
    -accel kvm \
    -smp 4 \
    -serial stdio \
    -device virtio-gpu-pci \
    -net nic -net user \
    -device nec-usb-xhci,id=xhci,addr=0x1b \
    -device usb-tablet,id=tablet,bus=xhci.0,port=1 \
    -device usb-kbd,id=keyboard,bus=xhci.0,port=2 \
    -hda archlinux-minimal-2024.04.23-loong64.qcow2 \
    -bios /usr/share/qemu-efi-loongarch64/QEMU_EFI.fd

Emulated/Virtualized environment

  • Operating system:

    ArchLinux

  • OS/kernel version:

    6.16

  • Architecture:

    Loongarch64

Description of problem

I have installed Debian sid on a loongarch machine. with Loongson 3A6000 CPU. The kernel in this OS is Linux 6.6, which is provided by Loongnix 25. After upgrading qemu-system-loongarch64 to 10.1, the qemu-system-loongarch64 command fails to work. The error message is

IPI KVM_CREATE_DEVICE failed: Operation not supported

I have tried to install different versions of qemu-system-loongarch64 in debian snapshot. version 1:10.0.3+ds-4 or lower works well and 1:10.1.0+ds-1 or higher versions failed to work.

I also tried to upgrade the kernel version to 6.16.7, and qemu-system-loongarch64 10.1 works. In conclusion, the problem happens with the combination of kernel 6.6 and qemu 10.1.

I also check the source code of qemu. The error message is introduced by a new function kvm_ipi_realize() in qemu 10.1 in file hw/intc/loongarch_ipi_kvm.c. This function is commited by Bibo Mao in commit 412f6555.

void kvm_ipi_realize(DeviceState \*dev, Error \*\*errp)

{

    LoongarchIPIState \*lis = LOONGARCH_IPI(dev);

int ret;

    ret = kvm_create_device(kvm_state, KVM_DEV_TYPE_LOONGARCH_IPI, false);

if (ret \< 0) {

fprintf(stderr, "IPI KVM_CREATE_DEVICE failed: %s\\n",

strerror(-ret));

abort();

    }

lis-\>dev_fd = ret;

}

Since kernel 6.6 is a long term version, qemu should support this version well or provide some compatibility plan at least.

Steps to reproduce

  1. Install Debian on a Loongson 3A6000 laptop computer with kernel 6.6.
  2. Install qemu-system-loongarch64 by "apt install qemu-system-misc"
  3. Download the virtual machine qcow2 file from https://loongarchlinux.org/pages/download/
  4. run the qemu command in the previous section.

Additional information

Edited by Ya-Fan Zhao