I bisected seabios and found this seabios change to be the cause of the problem
commit b837e68d5a6c1a5945513f1995875445a1594c8a (refs/bisect/bad) Author: Kevin O'Connor <ke...@koconnor.net> Date: Mon Nov 9 15:00:19 2015 -0500 resume: Make KVM soft reboot loop detection more flexible Move the check for soft reboot loops from resume.c to shadow.c and directly check for the case where the copy of the BIOS in flash appears to be a memory alias instead. This prevents a hang if an external reboot request occurs during the BIOS memcpy. Signed-off-by: Kevin O'Connor <ke...@koconnor.net> -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1747056 Title: FreeDOS / MS-Dos / Windows 3.11 cannot perform reboot with 'isapc' machine Status in QEMU: New Bug description: I was installing MS-Dos 6.22 + Windows 3.11 in preparation for running Microsoft Bob, and noticed that when they try to perform a reboot, they just get stuck. The console cursor stays flashing on/off, but the DOS prompt no longer responds to input. It is fairly easy to reproduce, even FreeDOS is impacted - download the FreeDOS bootable CDROM image, then $ qemu-img create demo.img 100MB $ qemu-system-x86_64 -machine isapc -cdrom ~/Downloads/FD12CD.iso -hda demo.img -monitor stdio Wait for the installer to startup, and then in the monitor console run sendkey ctrl-alt-delete It will fail to reboot Testing shows this is a regression from QEMU 2.8.0 onwards, and git bisect further narrowed it down to a SEABIOS update commit 6e99f5741ff1b408ea76e6caf2bd4f76df4060e9 (HEAD, tag: pull-seabios-20161027-2, tag: pull-seabios-20161027-1, refs/bisect/bad) Author: Gerd Hoffmann <kra...@redhat.com> Date: Thu Oct 27 16:42:28 2016 +0200 seabios: update to 1.10.0 release. Note that this seems particular to the "isapc" machine type - with the "pc" machine type, reboot still works To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1747056/+subscriptions