“RAMBleed has been demonstrated on devices with DDR3 memory chips, and Rowhammer's bit flipping on DDR4 components. DDR4 supports a defensive technique called Targeted Row Refresh, but its efficacy is uncertain. "Given the closed-source nature by which TRR is implemented, it is difficult for the security community to evaluate its effectiveness," said Kwong. "While bit flips have been demonstrated on TRR before, the extent to which TRR mitigates RAMBleed remains an open question."

https://www.theregister.co.uk/2019/06/11/rambleed_rowhammer_...