SR-IOV buffer allocation

I'm reading about SR-IOV but one thing is still not clear. Does it divide the TX/RX buffers evenly between VIFs, or those are shared resources?

I'm worried that, if the first case is valid, I'll end up with very small buffer chunks when I create 32+ VIFs and I'll have buffer overruns even with low/moderate traffic.

I'm planning to use Intel XXV710 (2x25 Gbps) NICs.