On 10/07/20 19:26, Jim Mattson wrote: >> Intel only has MAXPHYADDR > 46 on LA57 machines (because in general OSes >> like to have a physical 1:1 map into the kernel part of the virtual >> address space, so having a higher MAXPHYADDR would be of limited use >> with 48-bit linear addresses). > We all know that the direct map is evil. :-) > > Sorry it took me so long to get there. I didn't realize that Linux was > incapable of using more physical memory than it could map into the > kernel's virtual address space. (Wasn't that the whole point of PAE > originally?) Yes, but it's so slow that Linux preferred not to go that way for 64-bit kernels. That said, that justification for MAXPHYADDR==46 came from Intel processor architects, and when they say "OSes" they usually refer to a certain vendor from the Pacific north-west. Paolo
