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The overall goal of the change is to reduce the amount of work done in locore assembly, and defer as much as possible until pmap_bootstrap(). Currently, half the setup is done in assembly, and then we pass the l1pt address to pmap_bootstrap() where it is amended with other mappings. Inspiration and understanding has been taken from amd64's create_pagetables() routine, and I try to present the page table construction in the same way: a linear procedure with commentary explaining what we are doing and why. Thus the core of the new implementation is contained in pmap_create_pagetables(). Once pmap_create_pagetables() has finished, we switch to the new pagetable root and leave the bootstrap ones created by locore behind, resulting in a minimal 8kB of wasted space. Having the whole procedure in one place, in C code, allows it to be more easily understood, while also making it more amenable to future changes which depend on CPU feature/errata detection. Note that with this change the size of the early devmap is bumped up from one to four L2 pages (8MB). Reviewed by: markj MFC after: 1 month Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D45327 |
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