On Wed, Aug 17, 2016 at 04:40:29PM +0100, Mark Rutland wrote:
ARMv8.2 bumps the maximum address limit to 52 bits [1]. Architecturally, only the upper 8 bits of address are reserved for tagging (and this has been the case since the original ARMv8-A release), and all other bits are reserved.
Given the above, it seems possible/likely that we may see address spaces of up to 56 bits in future.
So shuffling bits along a few places is only likely to buy us some time, and won't solve the problem entirely.
Absolutely - but it's still something we need to do, now.
And I'm hoping that by the time > 48-bit VA becomes an issue, it will be an issue for Intel also, and we won't need to do all of the lifting on the ARM side.
Sure. I just wanted to make clear that there are already things in the pipe beyond 48-bit.
Indeed. And we need to stay on the ball with that, and try to ensure any changes we do from this point onwards are at least 56-bit safe. And start agitating against pointer tagging in general.
w.r.t. future lifting it depends on how quickly those ARMv8.2 systems appear.
Well, I would say it depends on: - how quickly those ARMv8.2 systems start implementing ginormous++ physical address space ranges for DRAM. - whether we can separate kernel/user VA handling before that happens.
/ Leif