linux-kernel - Re: [PATCH] x86: Hyper-V: register clocksource only if its advertised

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Date:	Fri, 25 Jan 2013 08:10:16 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Olaf Hering <olaf@...fle.de>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	KY Srinivasan <kys@...rosoft.com>
Subject: Re: [PATCH] x86: Hyper-V: register clocksource only if its advertised

On Fri, Jan 25, 2013 at 02:37:16PM +0100, Olaf Hering wrote:
> 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>
> Cc: stable@...nel.org
> Cc: KY Srinivasan <kys@...rosoft.com>
> Cc: Greg KH <gregkh@...uxfoundation.org>
> ---
>  arch/x86/kernel/cpu/mshyperv.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

This needs to go through the x86 maintainers, not me, sorry.

greg k-h
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