OverviewHistoryStatsSecurity
npx skills add ...
Documentation
SKILL.md
npx skills add mohitmishra786/low-level-dev-skills --skill qemu-kvm
QEMU/KVM skill for virtualization and kernel development. Use when running qemu-system-x86_64 with KVM, configuring virtio devices, VFIO passthrough, QMP monitor, libvirt, or booting custom kernels. Activates on queries about QEMU, KVM, virtio, VFIO, virsh, virt-install, or -kernel -append.
npx skills add mohitmishra786/low-level-dev-skills --skill qemu-kvm
Guide agents through QEMU system emulation and KVM acceleration: key qemu-system-x86_64 flags, virtio devices, VFIO device passthrough, QMP monitor protocol, libvirt/virsh management, and QEMU for kernel development with -kernel -initrd -append.
| Flag | Purpose |
|---|---|
-enable-kvm | Use KVM acceleration |
-cpu host | Pass through host CPU features |
-m | RAM in MB |
-smp | vCPU count |
-drive | Disk image |
-netdev / -device | Network backend |
Always prefer virtio over emulated devices for performance.
Requires IOMMU enabled (intel_iommu=on or amd_iommu=on in kernel cmdline).
| Symptom | Cause | Fix |
|---|---|---|
| KVM disabled warning | BIOS VT-x off or nested issue | Enable VT-x/AMD-V; check /dev/kvm |
| VM very slow | KVM not active | Add -enable-kvm; install kvm modules |
| VFIO group error | Device not in IOMMU group | Use find /sys/kernel/iommu_groups/ |
| No network in VM | Wrong netdev backend | user networking vs tap/bridge |
| Kernel panic on boot | Wrong root= or missing driver | Add virtio drivers to initrd |
| QMP connection refused | Socket not ready | Wait for QEMU start; check path |
skills/virtualization/hypervisor-internals — VT-x/SVM theory under KVMskills/kernel/kernel-testing — boot test kernels in QEMUskills/kernel/os-dev-scratch — minimal OS development in QEMUskills/kernel/kernel-debugging — kgdb with QEMU -s -Sskills/async-io/dpdk — DPDK with QEMU virtioskills/platform/riscv-privileged — qemu-system-riscv64# virtio-blk (paravirtual disk — faster)
-device virtio-blk-pci,drive=hd0 \
-drive if=none,id=hd0,file=disk.qcow2,format=qcow2
# virtio-net
-netdev tap,id=net0,ifname=tap0,script=no,downscript=no \
-device virtio-net-pci,netdev=net0
# virtio-balloon (dynamic memory)
-device virtio-balloon-pci
# virtio-scsi
-device virtio-scsi-pci,id=scsi0 \
-device scsi-hd,drive=hd0,bus=scsi0.0# Bind device to vfio-pci
echo 10de 1c03 | sudo tee /sys/bus/pci/drivers/vfio-pci/new_id
sudo virsh nodedev-detach pci_0000_01_00_0
# QEMU with passthrough
qemu-system-x86_64 \
-enable-kvm -m 8192 -smp 8 \
-device vfio-pci,host=01:00.0 \
...# Start with QMP socket
qemu-system-x86_64 ... \
-qmp unix:/tmp/qmp.sock,server,nowait
# Send QMP commands
socat - UNIX-CONNECT:/tmp/qmp.sock
{"execute":"qmp_capabilities"}
{"execute":"query-status"}
{"execute":"system_powerdown"}
{"execute":"savevm", "arguments":{"name":"checkpoint1"}}# Define VM from XML
virsh define myvm.xml
# Start/stop
virsh start myvm
virsh shutdown myvm
virsh destroy myvm # force power off
# Console
virsh console myvm
# Snapshot
virsh snapshot-create-as myvm snap1 "before upgrade"
# List
virsh list --all# Create VM interactively
virt-install \
--name ubuntu-vm \
--ram 4096 \
--vcpus 4 \
--disk path=/var/lib/libvirt/images/ubuntu.qcow2,size=20 \
--os-variant ubuntu22.04 \
--network bridge=virbr0 \
--graphics none \
--console pty,target_type=serial \
--location http://archive.ubuntu.com/ubuntu/dists/jammy/main/installer-amd64/ \
--extra-args 'console=ttyS0,115200n8'# Direct kernel boot (no disk install needed)
qemu-system-x86_64 \
-enable-kvm \
-m 512 \
-kernel arch/x86/boot/bzImage \
-initrd /path/to/initramfs.cpio.gz \
-append "console=ttyS0 root=/dev/sda rw nokaslr" \
-serial stdio \
-display none \
-no-reboot# With custom rootfs on virtio disk
-drive file=rootfs.ext4,format=raw,if=virtio \
-append "console=ttyS0 root=/dev/vda rw"# GDB stub for kernel
qemu-system-x86_64 \
-kernel bzImage -append "console=ttyS0 nokaslr" \
-s -S \ # -s = gdb port 1234, -S = wait for gdb
-serial stdio -display none
# Host GDB
gdb vmlinux
(gdb) target remote :1234
(gdb) break start_kernel
(gdb) continueqemu-img create -f qcow2 disk.qcow2 20G
qemu-img snapshot -c clean disk.qcow2
qemu-img convert -O raw disk.qcow2 disk.raw
qemu-img info disk.qcow2