[Qemu-devel] (i386) TCG is broken in 1.5-rc0 with guest kernel 3.2?

[Michael Tokarev <mjt@tls.msk.ru>]

Something strange is going on here.

I just tried 1.5-rc0 (32bit x86 userspace), and guest kernel
crashes in an interesting way right at init time.

 qemu-system-x86_64 -net none -kernel /boot/vmlinuz-3.2-amd64 -append console=ttyS0 -serial file:serial

This results in:

[    0.071315] mce: CPU supports 10 MCE banks
[    0.082316] SMP alternatives: switching to UP code
[    0.658457] Freeing SMP alternatives: 16k freed
[    0.660716] ACPI: Core revision 20110623
[    0.744749] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
[    0.778545] CPU0: AMD QEMU Virtual CPU version 1.4.90 stepping 03
[    0.887450] Performance Events: Broken PMU hardware detected, using software events only.
[    0.889372] NMI watchdog disabled (cpu0): hardware events not enabled
[    0.889372] Brought up 1 CPUs
[    0.889372] Total of 1 processors activated (6432.01 BogoMIPS).
[    0.889372] devtmpfs: initialized
[    0.889372] ------------[ cut here ]------------
[    0.889372] WARNING: at fs/sysfs/group.c:138 dpm_sysfs_add+0xb4/0xc0()
[    0.889372] Hardware name: Bochs
[    0.889372] sysfs group ffffffff814bece0 not found for kobject 'platform'
[    0.889372] Modules linked in:
[    0.889372] Pid: 1, comm: swapper/0 Not tainted 3.2.0-amd64 #3.2.42
[    0.889372] Call Trace:
[    0.889372]  [<ffffffff812791c4>] ? dpm_sysfs_add+0xb4/0xc0
...

[    0.889372] ---[ end trace ef00d87ab31a38ca ]---
[    0.889372] NET: Registered protocol family 16
[    0.889372] ------------[ cut here ]------------
[    0.889372] WARNING: at fs/sysfs/group.c:138 dpm_sysfs_add+0xb4/0xc0()
[    0.889372] Hardware name: Bochs
[    0.889372] sysfs group ffffffff814bece0 not found for kobject 'vtcon0'
[    0.889372] Modules linked in:
[    0.889372] Pid: 1, comm: swapper/0 Tainted: G        W    3.2.0-amd64 #3.2.42
[    0.889372] Call Trace:
[    0.889372]  [<ffffffff812791c4>] ? dpm_sysfs_add+0xb4/0xc0
...

and finally
[    0.889372] kernel BUG at kernel/params.c:780!
[    0.889372] invalid opcode: 0000 [#1] SMP
...
[    0.893968] Kernel panic - not syncing: Attempted to kill init!



The same happens with other 3.2.x kernels, for example, ubuntu precise:
http://archive.ubuntu.com/ubuntu/dists/precise/main/installer-amd64/current/images/netboot/ubuntu-installer/amd64/linux


qemu-system-x86_64 from qemu-1.4.x lets these kernels to boot fine,
it all boots fine when adding -enable-kvm.  So it is some change(s)
in TCG between 1.4 and 1.5, maybe triggering a bug in guest kernel.

For added fun, for example, 3.8 guest kernel does NOT have problems
with this config.

I'm trying to bisect the issue now.

This happened when CarlFK (Cc'd) mentioned that he has issues with
installing ubuntu precise in a 1.5 virtual machine.  But in his
case, the prob was different, -- his installer does not configure
NIC properly due to dhclient segfaulting, which, again, does not
happen with previous versions of qemu.  This may be related or
not, I don't know yet.

That's just a heads-up for now, will post more details as something
will become available.

Thanks,

/mjt