unaccelerated qemu is broken

Bug #975240 reported by Serge Hallyn on 2012-04-06
This bug affects 1 person
Affects Status Importance Assigned to Milestone
qemu-kvm (Debian)
Fix Released
qemu-kvm (Ubuntu)
Serge Hallyn

Bug Description

accelerated kvm works fine, but unaccelerated it hangs. To reproduce:

wget http://people.canonical.com/~jamie/libvirt/qatest.tar.bz2
tar jxf qatest.tar.bzw
cd qatest
qemu-system-x86_64 -no-kvm -m 128 -monitor stdio -vnc :0 -vga cirrus -usb -drive file=qatest.img,if=none,id=drive-ide0-0-0,format=raw -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1

You can connect to the vm with 'gvncviewer :0'. Some time after it starts loading the initramfs, qemu locks up. Typing into the stdio monitor is hung.

Enabling kvm, the vm boots fine.

Changed in qemu-kvm (Ubuntu):
importance: Undecided → Critical
status: New → Confirmed
status: Confirmed → In Progress
assignee: nobody → Serge Hallyn (serge-hallyn)
Jamie Strandboge (jdstrand) wrote :

I can confirm this. Booting with this works fine:
LC_ALL=C PATH=/bin:/usr/sbin:/sbin:/bin /usr/bin/qemu-system-i386 -m 128 -usb -drive file=/tmp/qatest.img,if=none,id=drive-ide0-0-0,format=raw -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1

Booting with this does not:
LC_ALL=C PATH=/bin:/usr/sbin:/sbin:/bin /usr/bin/qemu-system-i386 -no-kvm -m 128 -usb -drive file=/tmp/qatest.img,if=none,id=drive-ide0-0-0,format=raw -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1

FWIW, if I go into the grub menu and remove 'quiet splash' I see it stops at:

Adding '-no-acpi' allows it to boot.

Serge Hallyn (serge-hallyn) wrote :

Fixed upstream, fix bisected to 62db8bf39b8a0e3edb631a3d0e5bde840c780fcf: ARM: exynos4210: PWM support. That doesn't quite seem right, let me verify...

Serge Hallyn (serge-hallyn) wrote :

No, still broken with that commit, apparently I took a wrong turn while bisecting.

Serge Hallyn (serge-hallyn) wrote :

I believe 30628cb12de2e35d87cb04194113341b6a8922b2 is the fix

Serge Hallyn (serge-hallyn) wrote :


unfortunately for bisecting, it appears to not *always* hang.

Serge Hallyn (serge-hallyn) wrote :

ce967e2f33861b0e17753f97fa4527b5943c94b6 in qemu definately fixes it.

trying to cherrypick the equivalent commit from qemu-kvm upstream, though it appears to have pieces ofanother commit included and does not cherrypick cleanly.

Dave Walker (davewalker) on 2012-04-06
tags: added: rls-mgr-p-tracking
Changed in qemu-kvm (Debian):
status: Unknown → New
Serge Hallyn (serge-hallyn) wrote :

Per discussion on #qemu, the proposed fix simply enforces -no-hpet when kvm acceleration is not used.

Launchpad Janitor (janitor) wrote :

This bug was fixed in the package qemu-kvm - 1.0+noroms-0ubuntu11

qemu-kvm (1.0+noroms-0ubuntu11) precise; urgency=low

  * debian/patches/disable-hpet-for-tcg.patch: implicitly set -no-hpet
    when using tcg (non-accelerated qemu). (LP: #975240)
 -- Serge Hallyn <email address hidden> Mon, 09 Apr 2012 11:06:36 -0500

Changed in qemu-kvm (Ubuntu):
status: In Progress → Fix Released
Changed in qemu-kvm (Debian):
status: New → Fix Committed
Changed in qemu-kvm (Debian):
status: Fix Committed → Fix Released
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