Re: [PATCH 3.14] Drivers: hv: vmbus: prevent cpu offlining on newer hypervisors

[Luis Henriques <luis.henriques@canonical.com>]

On Mon, Mar 28, 2016 at 10:30:41AM -0400, Chas Williams wrote:
> 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>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> [ 3chas3@gmail.com: rebase to 3.14-stable ]

Thanks, I'm also queuing this for the 3.16 kernel as well.

Cheers,
--
Lu�s

> Signed-off-by: Chas Williams <3chas3@gmail.com>
> ---
>  drivers/hv/vmbus_drv.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 077bb1b..e3b7341 100644
> --- 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 int irq, struct irq_desc *desc)
>  	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);
>  }
>  
>  
> -- 
> 2.5.0
> 
> --
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