Patch "Drivers: hv: vmbus: prevent cpu offlining on newer hypervisors" has been added to the 3.14-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    Drivers: hv: vmbus: prevent cpu offlining on newer hypervisors

to the 3.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drivers-hv-vmbus-prevent-cpu-offlining-on-newer-hypervisors.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From e513229b4c386e6c9f66298c13fde92f73e6e1ac Mon Sep 17 00:00:00 2001
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: Fri, 27 Feb 2015 11:25:51 -0800
Subject: Drivers: hv: vmbus: prevent cpu offlining on newer hypervisors

From: Vitaly Kuznetsov <vkuznets@redhat.com>

commit e513229b4c386e6c9f66298c13fde92f73e6e1ac upstream.

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>
[ 3chas3@gmail.com: rebase to 3.14-stable ]
Signed-off-by: Chas Williams <3chas3@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/hv/vmbus_drv.c |   36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -31,6 +31,7 @@
 #include <linux/slab.h>
 #include <linux/acpi.h>
 #include <linux/completion.h>
+#include <linux/cpu.h>
 #include <linux/hyperv.h>
 #include <linux/kernel_stat.h>
 #include <asm/hyperv.h>
@@ -689,6 +690,39 @@ static void vmbus_flow_handler(unsigned
 	desc->action->handler(irq, desc->action->dev_id);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static int hyperv_cpu_disable(void)
+{
+	return -ENOSYS;
+}
+
+static void hv_cpu_hotplug_quirk(bool vmbus_loaded)
+{
+	static void *previous_cpu_disable;
+
+	/*
+	 * Offlining a CPU when running on newer hypervisors (WS2012R2, Win8,
+	 * ...) is not supported at this moment as channel interrupts are
+	 * distributed across all of them.
+	 */
+
+	if ((vmbus_proto_version == VERSION_WS2008) ||
+	    (vmbus_proto_version == VERSION_WIN7))
+		return;
+
+	if (vmbus_loaded) {
+		previous_cpu_disable = smp_ops.cpu_disable;
+		smp_ops.cpu_disable = hyperv_cpu_disable;
+		pr_notice("CPU offlining is not supported by hypervisor\n");
+	} else if (previous_cpu_disable)
+		smp_ops.cpu_disable = previous_cpu_disable;
+}
+#else
+static void hv_cpu_hotplug_quirk(bool vmbus_loaded)
+{
+}
+#endif
+
 /*
  * vmbus_bus_init -Main vmbus driver initialization routine.
  *
@@ -747,6 +781,7 @@ static int vmbus_bus_init(int irq)
 	if (ret)
 		goto err_alloc;
 
+	hv_cpu_hotplug_quirk(true);
 	vmbus_request_offers();
 
 	return 0;
@@ -984,6 +1019,7 @@ static void __exit vmbus_exit(void)
 	bus_unregister(&hv_bus);
 	hv_cleanup();
 	acpi_bus_unregister_driver(&vmbus_acpi_driver);
+	hv_cpu_hotplug_quirk(false);
 }
 
 


Patches currently in stable-queue which might be from vkuznets@redhat.com are

queue-3.14/drivers-hv-vmbus-prevent-cpu-offlining-on-newer-hypervisors.patch