This work describes ViSMI, a software distributed shared memory system for cluster systems connected via InfiniBand. ViSMI implements a kind of home-based lazy release consistency protocol, which uses a multiple-writer coherence scheme to alleviate the traffic introduced by false sharing. For further performance gain, InfiniBand features and optimized page invalidation mechanisms are applied in order to reduce synchronization overhead. First experimental results show that ViSMI introduces good performance comparable to similar software DSMs.