Architecture: x86_64

x86_64

Boards

• pc
• microvm

Memory management

During the early boot sequence, we identity map the first gigabyte of our kernel with 512 2MiB pages. When kmain() is called, paging_init() updates the mapping:

1. Memory from 0x00000000 to 0x000A0000 is identity mapped (present)
2. Memory from 0x000A0000 to 0x00100000 is identity mapped (present + writable)
3. The VBE framebuffer might be identity mapped as well (present + writable, and only if ENABLE_FRAMEBUFFER=1 is passed to make; only applicable to pc)
4. The kernel sections are identity mapped with the correct flags for each section
5. The board's boot information is identity mapped (the multiboot information on pc, the PVH hvm_start_info structure on microvm)
6. The board's boot modules are identity mapped with the correct flags (in our case, it is the init ramdisk)
7. The memory allocated for the frame allocator is then identity mapped

In addition, paging_init() will:

1. enable write protection
2. enable the no-execute feature
3. create a guard page

Memory map

Virtual address space

• 0x00000000 to 0x00100000: the first 1MiB area is reserved
• 0x00100000: the kernel code and data and boot modules
• 0x0020xxxx: after the end of the previous area (which is computed at runtime using the board's boot information), we allocate some space for the frame allocator
• 0x10000000: kernel heap area (we currently have a fixed heap size)
• 0x40000000: user space