xen/events: mask events when changing their VCPU binding
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: NDavid Vrabel <david.vrabel@citrix.com> Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com> Reviewed-by: NJan Beulich <jbeulich@suse.com> CC: stable@vger.kernel.org
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