linux-kernel - Re: [PATCH v3] Drivers: hv: vmbus: prevent cpu offlining on newer hypervisors

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Date:	Sun, 25 Jan 2015 21:36:59 +0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>,
	devel@...uxdriverproject.org,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	linux-kernel@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH v3] Drivers: hv: vmbus: prevent cpu offlining on newer
 hypervisors

On Mon, Jan 12, 2015 at 05:50:11PM +0100, Vitaly Kuznetsov wrote:
> When an SMP Hyper-V guest is running on top of 2012R2 Server and secondary
> cpus are sent offline (with echo 0 > /sys/devices/system/cpu/cpu$cpu/online)
> the system freeze is observed. This happens due to the fact that on newer
> hypervisors (Win8, WS2012R2, ...) vmbus channel handlers are distributed
> across all cpus (see init_vp_index() function in drivers/hv/channel_mgmt.c)
> and on cpu offlining nobody reassigns them to CPU0. Prevent cpu offlining
> when vmbus is loaded until the issue is fixed host-side.
> 
> This patch also disables hibernation but it is OK as it is also broken (MCE
> error is hit on resume). Suspend still works.
> 
> Tested with WS2008R2 and WS2012R2.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> ---
> Changes since v2:
> - repair the build when vmbus is builded as a module [Greg KH] by saving
>   current cpu_disable pointer to previous_cpu_disable and restoring it on
>   unload;
> - return -ENOSYS (same as native_cpu_disable when !CONFIG_HOTPLUG_CPU) instead
>   of -1 in hyperv_cpu_disable().
> 
> Changes since v1:
> - introduce hv_cpu_hotplug_quirk() function to not spread #ifdefs [Greg KH];
> - add pr_notice() message "hv_vmbus: CPU offlining is not supported by
>   hypervisor".
> ---
>  drivers/hv/vmbus_drv.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)

Doesn't apply to my char-misc-test branch at all :(
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