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I don't see how it will help. First, if the vendors can ship a new Linux kernel, they can as well ship updated firmware to increase memory refresh frequency. Se
by Marat_Dukhan 10y ago
I don't see how it will help. First, if the vendors can ship a new Linux kernel, they can as well ship updated firmware to increase memory refresh frequency. Secondly, on mobile devices CPU and GPU share the same memory, and it could be only a matter of time before we see GPU-powered rowhammer attack.
- angry_octet 10y agoWhy do you think the firmware would be capable of programming DRAM refresh rate to a heretofore unheard of frequency? This capability does not exist in the memory controller. It might be hard to get the GPU to hammer memory hard enough because of the caches (http://wccftech.com/intel-skylake-gen9-graphics-architecture-explained-gt2-24-eus-gt3-48-eus-gt4e-72-eus/ http://wccftech.com/intel-skylake-gen9-graphics-architecture...). Maybe with glBufferData in DRAW mode it would force uncached access, depends if the graphics core cache snoops the address bus (coherent) or not, in which case it could be tricked. However the AMD Fusion docs certainly seem to indicate it is possible, and significantly higher read bandwidth than from the CPU (http://developer.amd.com/wordpress/media/2013/06/1004_final.pdf http://developer.amd.com/wordpress/media/2013/06/1004_final....). Indeed, it makes me wonder why (given the repetitive read pattern required for updating VBOs) whether the system instability people have seen before is not due to the GPU doing unintentional rowhammer.
- Marat_Dukhan 10y agoI thought refresh rate is programmable. But if not, at least firmware could lower the DRAM frequency. Intel GPUs have write-back caches because they share L3 cache with CPU cores. AFAIK, other GPUs typically have write-through caches, which doesn't help against rowhammer.