Virtual Mapper

This is implemented in virtual_memory_mapper

This is where we map physical memory to virtual memory, and where virtual memory pages are managed after [boot].

The main features is to map and unmap physical memory to virtual memory, and to allocate and free virtual memory pages.

The map function takes 1 argument VirtualMemoryMapEntry which is a struct contains information about the mapping:

#![allow(unused)]
fn main() {
pub struct VirtualMemoryMapEntry {
    pub virtual_address: usize,
    pub physical_address: Option<u64>,
    pub size: usize,
    pub flags: u64,
}
}

virtual_address is the virtual address to map to, and must be known of course
physical_address is the physical address to map to, if its None, then we will allocate new memory from the [physical allocator]
size is the size of the mapping, must be 4K aligned
flags is the flags of the mapping, such as Writable, UserAccessible. For now, these are just constants mapping directly to x86 page table flags.

The unmap function takes the same struct, but physical_address must be None, and virtual_address must be known, it also takes is_allocated which is a boolean to indicate if the memory was allocated by the virtual memory mapper, if it was, it will be freed.

This API can be improved, but currently we don't keep track of the mappings, so we rely on the caller to do that for us :D.

Beside that, we got other functionalities used by processes. Like:

switch_to_this: to switch to the self VirtualMemoryMapper, which each process has its own VirtualMemoryMapper.
get_current_vm: to get the current VirtualMemoryMapper of the current process.
clone_current_vm_as_user: Clones the kernel mappings of the current vm, and mark it as user vm, so it doesn't allow kernel mappings anymore.

boot physical allocator

Emerald

Virtual Mapper