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Improve Paging Implementation Post #666

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merged 5 commits into from Sep 14, 2019

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commented Sep 14, 2019

This pull request cleans up and improves the Paging Implementation post in a number of places:

  • New Content: Create a new Choosing a Virtual Page subsection that explains in detail when additional page table frames are required from the frame allocator and when not. This also includes a new figure.
  • Code Fix: Use page 0 instead of 0x1000 for the example mapping because the new bootloader version now maps 0x1000 itself, so that a 'page already mapped' error would occur.
  • Code Simplification: Use the new OffsetPageTable type instead of MappedPageTable. This avoids the use of impl Trait as a return type, which can lead to problems when trying to store the returned type in a static variable (since you can't name the type).
  • Code Change: Update the functions of the memory module to take the physical_memory_offset as a VirtAddr instead of a plain u64. This makes it clearer that the address is virtual and also simpler to calculate the virtual address for a physical address (no more Virt::new).
  • Code Change: Simplify the signature of the create_example_mapping function by taking an OffsetPageTable type as an argument instead of an impl Trait argument. (It is unlikely that the function is called with different mapper types.)
  • Clean-Up: Remove the "Another Paging Post?" aside at the beginning that mentioned the old "Advanced Paging" post and the reasons for writing a new version of the post. The new version is now already more than seven months old, so there's is no need to mention the previous version anymore.
  • Other: Update the screenshots and stack addresses for the new bootloader version to avoid confusion (the new bootloader version changed stack placement).

The required updates to the post-09 branch are implemented in #667. See the diff for an overview of the code changes induced by this PR.

phil-opp added 5 commits Sep 11, 2019
It's been a while since we removed the old Advanced Paging post.
Bootloader 0.8.0 maps the page at 0x1000 itself.
@phil-opp phil-opp added the relnotes label Sep 14, 2019
@phil-opp phil-opp merged commit d4d853c into master Sep 14, 2019
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@phil-opp phil-opp deleted the offset_page_table branch Sep 14, 2019
@phil-opp phil-opp added this to Done in Roadmap Sep 14, 2019
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