>       if (rbi->ring_buffer->feature_bits.feat_pending_send_sz) {
>               u32 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
>  
>               /*
> +              * Ensure the read of write_index in hv_get_bytes_to_write()
> +              * happens after the read of pending_send_sz.
> +              */
> +             virt_rmb();
> +             curr_write_sz = hv_get_bytes_to_write(rbi);
> +
> +             /*
>                * If there was space before we began iteration,
>                * then host was not blocked. Also handles case where
>                * pending_sz is zero then host has nothing pending
>                * and does not need to be signaled.
>                */
> -             if (orig_write_sz > pending_sz)
> +             if (curr_write_sz - delta > pending_sz)
>                       return;
>  
>               /* If pending write will not fit, don't give false hope. */
> -             if (hv_get_bytes_to_write(rbi) < pending_sz)
> +             if (curr_write_sz <= pending_sz)
>                       return;
> +
> +             vmbus_setevent(channel);
>       }
>  
> -     vmbus_setevent(channel);
>  }

I think this won't work on older versions of Windows where feat_pending_sz
is never set.  On those versions vmbus_setevent needs to always be called.

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