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

[Vitaly Kuznetsov]

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@xxxxxxxxxx>
---
 drivers/hv/vmbus_drv.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 4d6b269..9a82249 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -32,6 +32,7 @@
 #include <linux/completion.h>
 #include <linux/hyperv.h>
 #include <linux/kernel_stat.h>
+#include <linux/cpu.h>
 #include <asm/hyperv.h>
 #include <asm/hypervisor.h>
 #include <asm/mshyperv.h>
@@ -671,6 +672,13 @@ static void vmbus_isr(void)
 		tasklet_schedule(&msg_dpc);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static int hyperv_cpu_disable(void)
+{
+	return -1;
+}
+#endif
+
 /*
  * vmbus_bus_init -Main vmbus driver initialization routine.
  *
@@ -711,6 +719,12 @@ static int vmbus_bus_init(int irq)
 	if (ret)
 		goto err_alloc;
 
+#ifdef CONFIG_HOTPLUG_CPU
+	if ((vmbus_proto_version != VERSION_WS2008) &&
+	    (vmbus_proto_version != VERSION_WIN7))
+		smp_ops.cpu_disable = hyperv_cpu_disable;
+#endif
+
 	vmbus_request_offers();
 
 	return 0;
@@ -964,6 +978,11 @@ static void __exit vmbus_exit(void)
 	bus_unregister(&hv_bus);
 	hv_cleanup();
 	acpi_bus_unregister_driver(&vmbus_acpi_driver);
+#ifdef CONFIG_HOTPLUG_CPU
+	if ((vmbus_proto_version != VERSION_WS2008) &&
+	    (vmbus_proto_version != VERSION_WIN7))
+		smp_ops.cpu_disable = native_cpu_disable;
+#endif
 }
 
 
-- 
1.9.3

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