Defending against Rowhammer in the kernel

The hardware mitigation for rowhammer is LPDDR4's optional TRR feature (target row refresh). The memory manufacturers can still screw things up by caring more about performance (timings) and yields than creating a robust product. ECC is nice as an extra layer, but it's not a direct mitigation. It can often turn rowhammer into a denial of service instead of something worse, but it's not a guarantee.