qemu-troubleshooting.md

QEMU Troubleshooting Guide

Common issues encountered when running the linux-inference-memory-hints project in QEMU.

1. Patch Application Failure

• Symptoms: scripts/build_kernel.sh fails during the git am phase.
• Cause: The base kernel version (6.6.x) may have drifted significantly, or the patches were applied out of order.
• Fix: Ensure you are using the exact version specified in build_kernel.sh (6.6.20). Try rm -rf kernel-build and restart.

2. Kernel Panic on Boot

• Symptoms: QEMU hangs or loops after "End of boot".
• Cause: Usually a missing init in the rootfs or incorrect root= parameter.
• Fix: Verify your rootfs.ext4 contains a valid /sbin/init or /bin/sh.

3. 9p Mount Failure

• Symptoms: scripts/run_in_vm.sh fails to find /mnt/repo.
• Cause: The guest kernel lacks CONFIG_NET_9P or CONFIG_9P_FS.
• Fix: build_kernel.sh enables these via defconfig. If using a custom config, ensure 9P support is built-in (not a module).

4. Semantic Hints Still Unsupported

• Symptoms: verify_semantic_pipeline.sh reports [UNSUPPORTED].
• Cause: You may be booting an old bzImage instead of the newly patched one.
• Fix: Check uname -r inside the VM and verify it matches your build timestamp.

5. No pgscan/pgsteal Movement

• Symptoms: Reclaim counters stay at zero.
• Cause: Insufficient memory pressure.
• Fix: Increase the background load in memory_pressure or reduce the VM RAM (e.g., -m 1G).

6. DebugFS Unavailable

• Symptoms: /sys/kernel/debug is empty.
• Fix: Run mount -t debugfs none /sys/kernel/debug inside the guest.