Instead of building nested page tables for the offset region, just
offset map the entire thing into kernel memory with one PDP mapping
1GiB large pages. This is more efficient and avoids the "need a
page table to map in a page table" dependency loop.
2MiB large pages were being used for any large page mapping, but the
page manager doesn't correctly handle them everywhere yet. Now only
allow them for offset pointers (eg MMIO space) that will never be
unmapped.
Removed the frame allocation logic from page_manager and replaced it
with using an instance of frame_allocator instead. This had several
major ripple effects:
- memory_initalize() had to change to support this new world
- Where to map used blocks is now passed as a flag, since blocks don't
track their virtual address anymore
- Instead of the complicated "find N contiguous pages that can be
mapped in with one page table", we now just have the bootloader give
us some (currently 64) pages to use both for tables and scratch
space.
- frame_allocator initialization was split into two steps to allow
mapping used blocks before std::move()ing them over
* Heap manager can now manage non-contiguous blocks of memory (currently
all sized at the max block size only)
* Fix a bug where heap manager would try to buddy-merge max-sized blocks
The syscall/sysret instructions don't swap stacks. This was bad but
passable until syscalls caused the scheduler to run, and scheduling a
task that paused due to interrupt.
Adding a new (hopefully temporary) syscall interrupt `int 0xee` to allow
me to test syscalls without stack issues before I tackle the
syscall/sysret issue.
Also implemented a basic `pause` syscall that causes the calling process
to become unready. Because nothing can wake a process yet, it never
returns.
More work on process page tables, including only mapping the last 2 pml4
entries (the highest 1TiB of the address space, ie, kernel space) into a
new table.
Includes the work of actually moving the kernel there, which I had
apparently done in name only previously. Oops.
