RE: [PATCH v3] Drivers: hv: vmbus: prevent cpu offlining on newer hypervisors

[KY Srinivasan <kys@microsoft.com>]

> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
> Sent: Monday, January 26, 2015 2:39 AM
> To: Greg Kroah-Hartman
> Cc: KY Srinivasan; devel@linuxdriverproject.org; Haiyang Zhang; linux-
> kernel@vger.kernel.org; Dexuan Cui
> Subject: Re: [PATCH v3] Drivers: hv: vmbus: prevent cpu offlining on newer
> hypervisors
> 
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
> 
> > 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@redhat.com>
> >> Signed-off-by: K. Y. Srinivasan <kys@microsoft.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 :(
> 
> Another mid-air collision with K.Y's "Drivers: hv: vmbus: Implement a
> clockevent device", please use the attached version. No functional changes
> are required, I just fixed the merge conflict (includes).
> 
> Othere than that (and sorry for meddling), would it it be better if you switch
> to 'pull requests' workflow with K.Y? There is a lot of ongoing work in hyperv
> nowdays and such collisions seem otherwise inevitable ...

I will co-ordinate and forward Hyper-V patches to Greg.

K. Y
> 
> --
>   Vitaly