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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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