Linux KVM - dirty-page tracking without a vCPU on a dying VM: KVM warned (and on panic_on_warn hosts, panicked)

Impact

KVM warned (and on panic_on_warn hosts, panicked) when a page was marked dirty without an associated vCPU while a VM was being torn down. A guest that can arrange the teardown timing turns a warning into a host crash on any fleet running panic_on_warn - which plenty of hardened kernels do.

Who can reach it

From inside a guest, by timing VM teardown. Tenant-reachable.

What to do

Fixed in the Linux kernel. Take the distro kernel update (RHEL/Rocky, Ubuntu, SLES) and reboot the host - no firmware, VBIOS or AGESA step. On a GPU fleet this is a cordon, drain and rolling reboot; plan it as normal kernel maintenance. If you run panic_on_warn on GPU hosts for crash-dump fidelity, note that it converts warning-class kernel bugs like this into fleet availability incidents - worth reviewing that setting alongside the patch.

References