linux-kernel - [ 047/153] x86: Hyper-V: register clocksource only if its advertised

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Message-Id: <20130304033712.224331463@decadent.org.uk>
Date:	Mon, 04 Mar 2013 03:37:54 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, Olaf Hering <olaf@...fle.de>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [ 047/153] x86: Hyper-V: register clocksource only if its advertised

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Olaf Hering <[mailto:olaf@...fle.de]>

commit 32068f6527b8f1822a30671dedaf59c567325026 upstream.

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@...fle.de>
Link: http://lkml.kernel.org/r/1359940959-32168-1-git-send-email-kys@microsoft.com
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kernel/cpu/mshyperv.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -68,7 +68,8 @@ static void __init ms_hyperv_init_platfo
 	printk(KERN_INFO "HyperV: features 0x%x, hints 0x%x\n",
 	       ms_hyperv.features, ms_hyperv.hints);
 
-	clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100);
+	if (ms_hyperv.features & HV_X64_MSR_TIME_REF_COUNT_AVAILABLE)
+		clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100);
 }
 
 const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {


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