I agree that rowhammer needs a hardware-based defense. While ECC isn't prohibitively expensive and has negligible performance cost, keep in mind it's only a parity check with a proprietary implementation. There's some multiple of bit flips that will pass the parity check and still achieve the attacker's intended result, and the exploit is definitely going to get multiple attempts - if you get pwned the malicious process might be in memory and hammering away for hours, maybe it's even dropped a registry key to make sure it auto runs next boot.

Reference: http://blog.erratasec.com/2015/03/some-notes-on-dram-rowhamm...