Re: [Xen-devel] [PATCH 4/4] xen/events: mask events when changing their VCPU binding

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.08.13 at 14:21, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> When a event is being bound to a VCPU there is a window between the
> EVTCHNOP_bind_vpcu call and the adjustment of the local per-cpu masks
> where an event may be lost.  The hypervisor upcalls the new VCPU but
> the kernel thinks that event is still bound to the old VCPU and
> ignores it.
> 
> There is even a problem when the event is being bound to the same VCPU
> as there is a small window beween the clear_bit() and set_bit() calls
> in bind_evtchn_to_cpu().  When scanning for pending events, the kernel
> may read the bit when it is momentarily clear and ignore the event.
> 
> Avoid this by masking the event during the whole bind operation.
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

Interesting that this got lost at some point of the porting from the
XenoLinux tree.

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


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