Re: [Xen-devel] [PATCH V2] common/vm_event: synchronize vCPU state in vm_event_resume()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.08.16 at 09:35, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> --- a/xen/common/vm_event.c
> +++ b/xen/common/vm_event.c
> @@ -388,6 +388,13 @@ void vm_event_resume(struct domain *d, struct 
> vm_event_domain *ved)
>          v = d->vcpu[rsp.vcpu_id];
>  
>          /*
> +         * Make sure the vCPU state has been synchronized for the custom
> +         * handlers.
> +         */
> +        if ( atomic_read(&v->vm_event_pause_count) )
> +            sync_vcpu_execstate(v);

It seems to me that the latest with this change using a simple
atomic_t won't suffice anymore - you'd now really need to
make sure the user mode tools can't resume that vCPU behind
your back, which aiui can only be achieved by using a suitable
lock (perhaps a read/write one if reading the pause count is
more common than updating it).

Jan


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