x86: Hyper-V: register clocksource only if its advertised
authorOlaf Hering <[mailto:olaf@aepfle.de]>
Mon, 4 Feb 2013 01:22:37 +0000 (17:22 -0800)
committerH. Peter Anvin <hpa@linux.intel.com>
Wed, 13 Feb 2013 00:25:48 +0000 (16:25 -0800)
commit32068f6527b8f1822a30671dedaf59c567325026
treed9155252ffcd2f19de4e0dc87a80162617dbc45c
parent836dc9e3fbbab0c30aa6e664417225f5c1fb1c39
x86: Hyper-V: register clocksource only if its advertised

Enable hyperv_clocksource only if its advertised as a feature.
XenServer 6 returns the signature which is checked in
ms_hyperv_platform(), but it does not offer all features. Currently the
clocksource is enabled unconditionally in ms_hyperv_init_platform(), and
the result is a hanging guest.

Hyper-V spec Bit 1 indicates the availability of Partition Reference
Counter.  Register the clocksource only if this bit is set.

The guest in question prints this in dmesg:
 [    0.000000] Hypervisor detected: Microsoft HyperV
 [    0.000000] HyperV: features 0x70, hints 0x0

This bug can be reproduced easily be setting 'viridian=1' in a HVM domU
.cfg file. A workaround without this patch is to boot the HVM guest with
'clocksource=jiffies'.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Link: http://lkml.kernel.org/r/1359940959-32168-1-git-send-email-kys@microsoft.com
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Cc: <stable@vger.kernel.org>
Cc: Greg KH <gregkh@linuxfoundation.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
arch/x86/kernel/cpu/mshyperv.c