I haven't checked it through, and it was written at 3 AM
Task Unit
* Physical Memory
o Setup segments
o Page Stack, allocate and free
* Virtual Memory
o Memory Regions
o Memory Objects
o Stack Allocation
* Scheduler
* Threads
* Processes
Process creation
In kernel space, no page dir change during operation.
1. Allocate physical memory one page for the page dir
2. Allocate virtual memory one page and map it to 1.
3. Map a fixed address to 1. (the mapper has to check whether the page table is loaded or not, if it isn't, it has to allocate a phys. page for a new one)
4. Allocate virtual memory for the process data
5. Set the process data (causing a page fault, mapping the virtual address to a new page)
6. Attach memory regions to the process (rules for the page fault handler on how to map data)
7. Insert the process into the global process list
Thread creation
In a process.
1. Change page dir to the kernel process' page dir
2. Allocate virtual memory for the thread datastructure
3. The thread base address should already be mapped in the current process, if it isn't, it has to map the whole code
4. Allocate virtual memory for the stack
5. Insert the thread into the process
Page Fault
In a process.
1. Check the address against all memory regions in the process
2. If there is no region overlapping that address, allocate a new page and map
3. If there is a region overlapping, map as said by that object, like "allocate new page" or "use this page" or if the page is in the object's mapping list, it will use that address to map to
Syscall (or any other interrupt/IRQ/exception)
In a process.
1. Program calls int 0x80
2. int handler 0x80 is at the same address in all processes (mapping rule, first 2 MiB mapped 1:1, read only)
3. int handler switches page dir to the kernel process page dir, no write to RAM needed. Gained writable memory.
4. Executes the interrupt as usual, it's now in kernel space.
5. Switch back to the process' page dir
6. iret
