By: Chester (lamchester.delete@this.gmail.com), January 7, 2021 9:14 pm
Room: Moderated Discussions
> How is that going to help? Refreshing the memory will just
> "refresh" the flipped bits and you won't know a thing.
No, not software refresh. I'm talking about refreshing the charge in DRAM cell capacitors. Rowhammer can happen because accessing adjacent cells can cause a cell's charge to leak faster. If enough of it leaks before a charge refresh, you get a bit flip. Read https://arxiv.org/pdf/1904.09724.pdf for more details, in the 'Rowhammer Mechanisms' section.
> Currently some RAM manufactures are offering LPDDR4 modules with on-board ECC and from
> what I've seen it is mandatory for DDR5/LPDDR5. The intent of ECC in these instances
> is not to increase overall memory reliability/resiliency but to enable reduced power
> consumption partly through lessened refresh rates. Back to square one. Sheesh!
I think that's asking for trouble.
By the way, DRAM manufacturers have also tried targeted row refresh in hopes of mitigating rowhammer without tightening global refresh timings. But researchers have figured out ways past that too. Depending on the specific implementation of targeted row refresh, you can sometimes cause bit flips by hammering more rows.
> "refresh" the flipped bits and you won't know a thing.
No, not software refresh. I'm talking about refreshing the charge in DRAM cell capacitors. Rowhammer can happen because accessing adjacent cells can cause a cell's charge to leak faster. If enough of it leaks before a charge refresh, you get a bit flip. Read https://arxiv.org/pdf/1904.09724.pdf for more details, in the 'Rowhammer Mechanisms' section.
> Currently some RAM manufactures are offering LPDDR4 modules with on-board ECC and from
> what I've seen it is mandatory for DDR5/LPDDR5. The intent of ECC in these instances
> is not to increase overall memory reliability/resiliency but to enable reduced power
> consumption partly through lessened refresh rates. Back to square one. Sheesh!
I think that's asking for trouble.
By the way, DRAM manufacturers have also tried targeted row refresh in hopes of mitigating rowhammer without tightening global refresh timings. But researchers have figured out ways past that too. Depending on the specific implementation of targeted row refresh, you can sometimes cause bit flips by hammering more rows.