On Thu, Dec 08, 2022 at 12:18:07AM +0000, Sean Christopherson wrote: [...] > Together, what about? The #ifdef is a bit gross, especially around "hi_start", > but it's less duplicate code. And IMO, having things bundled in the same place > makes it a lot easier for newbies (to arm64 or kernel coding in general) to > understand what's going on and why arm64 is different. I'd rather we not go this route. We really shouldn't make any attempt to de-dupe something that is inherently architecture specific. For example: > + /* > + * All architectures supports splitting the virtual address space into > + * a high and a low half. Populate both halves, except for arm64 which > + * currently uses only TTBR0_EL1 (arbitrary selftests "logic"), i.e. > + * only has a valid low half. > + */ > + sparsebit_num_t nr_va_bits = (1ULL << (vm->va_bits - 1)) >> vm->page_shift; This is still wrong for arm64. When we say the VA space is 48 bits, we really do mean that TTBR0 is able to address a full 48 bits. So this truncates the MSB for the addressing mode. With the code living in the arm64 side of the shop, I can also tailor the comment to directly match the architecture to provide breadcrumbs tying it back to the Arm ARM. -- Thanks, Oliver
