On Wed, Aug 17, 2016 at 04:16:37PM +0100, Leif Lindholm wrote: > On Wed, Aug 17, 2016 at 04:03:07PM +0100, Mark Rutland wrote: > > > ARM64 platforms with > 512GB between the lowest and highest RAM > > > addresses end up getting their amount of usable memory truncated if > > > the kernel is built for 39-bit VA (which is what currently happens for > > > Debian kernels). For 4.7, the arm64 defconfig was changed to enable > > > 48-bit VA by default. > > > > > The problem is - some pieces of software have had time to be written > > > in a ... let's charitably call it a "focused on amd64" fasion ... with > > > the embedded assumption that anything above virtual address bit 44 is > > > a pointer-tag free-for-all. > > > > I suspect that we're likely to fall further into this. > > > > 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. w.r.t. future lifting it depends on how quickly those ARMv8.2 systems appear. Thanks, Mark. _______________________________________________ cross-distro mailing list cross-distro@lists.linaro.org https://lists.linaro.org/mailman/listinfo/cross-distro