Virtual memory manager

[arthurmco]

Do a virtual memory manager

It should have functions to:

• Allocate a virtual address from some zone, with some allocated physical address, from some other physical zone.

  • One function might return the physical address too (for things like DMA, that need a physical address but any physical from a certain zone)
  • The another do not need to return the physical address.

• Allocate a virtual address from some zone, with a specific physical address. (for things like MMIO, that need a certain, exact physical address)

(Check #5 for some clarification about physical addresses, specially this comment )

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It should be divided in zones: just a zone for kernel memory and other for user memory.

It should have a function to switch the CR3 (the page directory base register (PDBR), a register where the physical address of the page directory list go), so it's easy to do it for usermode (each process will have it's own page directory).

[arthurmco]

Need to setup some preliminary tables at boot, so we can use higher half addressing (kernel mapped at the higher half, > 0x8000000 virtual) from the start. Every major OS does that. Might help. Read http://wiki.osdev.org/Higher_Half_Kernel, it has more arguments than I do.

[arthurmco]

See 5e1d877. It's a beginning.

Higher half is used.

[arthurmco]

Added allocation methods at 82b0a16.

But we still have to do

• allocation of uncontiguous physical pages. This isn't possible yet.
• deallocation of virtual pages
• checking if that virtual page allocation can be contiguous. We allocate only contiguous virtual pages.

After doing the tasks above, this issue should be closed

[arthurmco]

1dae61f does deallocation.

It also adds a flag to the mapping. It maps with the page table mapping options, such as read-only page, or non-cached page.

[arthurmco]

I'm thinking about doing the heap allocator (#7 ) now.

It would help catching some errors in the VMM, since it's the only thing I can't test separately, prior to put here (the PMM was tested a little in user mode before integrating here, and I'm doing the heap allocator in user mode too)