Re: [Xen-devel] [PATCH v4] x86/vpmu: add cpu hot unplug notifier for vpmu

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 05/26/2017 10:05 AM, Jan Beulich wrote:
>>>> On 22.05.17 at 22:45, <luwei.kang@xxxxxxxxx> wrote:
>> Currently, Hot unplug a physical CPU with vpmu enabled may cause
>> system hang due to send a remote call to an offlined pCPU. This
>> patch add a cpu hot unplug notifer to save vpmu context before
>> cpu offline.
>>
>> Consider one scenario, hot unplug pCPU N with vpmu enabled.
>> The vcpu which running on this pCPU will be switch to other
>> online cpu. A remote call will be send to pCPU N to save the
>> vpmu context before loading the vpmu context on this pCPU.
>> System will hang in function on_select_cpus() because of that
>> pCPU is offlined and can not do any respond.
>>
>> The purpose of add a VPMU_CONTEXT_LOADED check in vpmu_arch_destroy()
>> before send a remote call to save vpmu contex is:
>> a. when a vpmu context has been loaded in a remote pCPU, make a
>>    remote call to save the vpmu contex and stop counters is necessary.
>> b. VPMU_CONTEXT_LOADED flag will be reset if a pCPU is offlined.
>>    this check will prevent send a remote call to an offlined pCPU.
>>
>> Signed-off-by: Luwei Kang <luwei.kang@xxxxxxxxx>
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> partly on the basis that Boris had agreed with how the change
> is being done, so Boris, an R-b from you would be nice.

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

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