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

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index f518b8d7a5b5190eb01b741d0961f6b9fbf6cd33..3b18a665ef4ce50c91f148d0fad1568db1ce9c98 100644 (file)
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -33,6 +33,7 @@
 #include <linux/hyperv.h>
 #include <linux/kernel_stat.h>
 #include <linux/clockchips.h>
+#include <linux/cpu.h>
 #include <asm/hyperv.h>
 #include <asm/hypervisor.h>
 #include <asm/mshyperv.h>
@@ -704,6 +705,39 @@ static void vmbus_isr(void)
        }
 }
 
+#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.
  *
@@ -744,6 +778,7 @@ static int vmbus_bus_init(int irq)
        if (ret)
                goto err_alloc;
 
+       hv_cpu_hotplug_quirk(true);
        vmbus_request_offers();
 
        return 0;
@@ -997,6 +1032,7 @@ static void __exit vmbus_exit(void)
        bus_unregister(&hv_bus);
        hv_cleanup();
        acpi_bus_unregister_driver(&vmbus_acpi_driver);
+       hv_cpu_hotplug_quirk(false);
 }