Lab 05

NCTU OSDI Lab 5: Virtual memory

Documentation: Lab 5

Lab 5 Demo Release

Required

• Required 1
  • Set up TCR_EL1.
  • Set up MAIR_EL1.
  • Set up identity mapping.
  • Modify linker script and map the upper address space.
  • Linear map kernel with finer granularity and map RAM as normal memory.
• Requried 2
  • Implement page bookkeeping.
  • Implement the translation function between kernel virtual address, physical address, PFN and the reference to struct page.
  • Implement page_alloc and page_free.
• Required 3
  • Implement user space paging.
  • Implement a minimum user library.
  • Implement shell as an user program and use objcopy to turn the ELF file into a raw binary.
  • Embed your shell binary to kernel image.
  • Allocate one page frame for user stack and map user task’s stack to the common address.
  • Set TTBR0_EL1 to switch between different address space when context switch.
• Required 4
  • Implement page frame reclaim.
  • Implement simple page fault handler.

Elective

• Elective 1
  • Implement mmap for creating a new region.
  • Implement Region page mapping.
• Elective 2
  • Parse the ELF header.
  • Implement ELF mapping.
• Elective 3
  • Implement demand paging.
• Elective 4
  • Implement copy-on-write.

Questions

• Without indirect branch, the code might still work fine, why it’s the case and why it’s mandatory to use indirect branch.
• For mapping 1GB memory region, how many page frames are used by page tables(PGD, PUD, PMD, and PTE) in four level translation?
• If a page frame is allocated and to be mapped at user space. Is it necessary to initialize it into 0?