feat(pagin): add WIP kernel remap

Signed-off-by: Julien CLEMENT <julien.clement@epita.fr>

src/memory/frame_allocator.rs

@@ -92,3 +92,37 @@ impl FrameDeallocator<Size4KiB> for AreaFrameAllocator {
         unimplemented!()
     }
 }
+
+pub struct TinyAllocator([Option<Frame>; 3]);
+
+impl TinyAllocator {
+    pub fn new<A>(allocator: &mut A) -> TinyAllocator
+        where A: FrameAllocator<Size4KiB>
+    {
+        let mut f = || allocator.allocate_frame();
+        let frames = [f(), f(), f()];
+        TinyAllocator(frames)
+    }
+}
+
+unsafe impl FrameAllocator<Size4KiB> for TinyAllocator {
+    fn allocate_frame(&mut self) -> Option<Frame> {
+        for frame_option in &mut self.0 {
+            if frame_option.is_some() {
+                return frame_option.take();
+            }
+        }
+        None
+    }
+}
+impl FrameDeallocator<Size4KiB> for TinyAllocator {
+    unsafe fn deallocate_frame(&mut self, frame: Frame) {
+        for frame_option in &mut self.0 {
+            if frame_option.is_none() {
+                *frame_option = Some(frame);
+                return;
+            }
+        }
+        panic!("Tiny allocator can hold only 3 frames.");
+    }
+}

src/memory/paging/mod.rs

@@ -1,19 +1,97 @@
 use multiboot2::BootInformation;
-use x86_64::structures::paging::{FrameAllocator, Size4KiB, PageTable, RecursivePageTable, Page, PageTableFlags as Flags, Mapper};
+pub use x86_64::structures::paging::{FrameAllocator, Size4KiB, PageTable, RecursivePageTable, Page, PageTableFlags as Flags, Mapper, PhysFrame as Frame};
 use crate::println;
-use x86_64::VirtAddr;
+use x86_64::{VirtAddr, PhysAddr};
+use x86_64::registers::control;
+use temporary_page::TemporaryPage;
+use super::PAGE_SIZE;
+
+mod temporary_page;
 
 pub const P4: *mut PageTable = 0o177777_777_777_777_777_0000 as *mut _;
 
-pub fn kernel_remap<A>(_allocator: &mut A, _boot_info: &BootInformation)
+pub fn kernel_remap<A>(allocator: &mut A, boot_info: &BootInformation)
     where A: FrameAllocator<Size4KiB>
 {
+    let mut temporary_page = TemporaryPage::new(Page::containing_address(VirtAddr::new(0xcafebabe)), allocator);
+    let mut active_table = get_active_page_table();
+    let mut new_table = {
+        let frame = allocator.allocate_frame().expect("No more frames");
+        InactivePageTable::new(frame, &mut active_table, &mut temporary_page)
+    };
+    new_table.under(&mut active_table, &mut temporary_page, |mapper| {
+        let elf_sections_tag = boot_info.elf_sections_tag().expect("Elf sections tag required");
+
+        for section in elf_sections_tag.sections() {
+            if !section.is_allocated() {
+                // section is not loaded to memory
+                continue;
             }
+            assert!(section.start_address() % PAGE_SIZE == 0,
+                    "sections need to be page aligned");
+
+            println!("mapping section at addr: {:#x}, size: {:#x}",
+                section.addr, section.size);
+
+            let flags = Flags::WRITABLE;
+
+            let start_frame = Frame::<Size4KiB>::containing_address(PhysAddr::new(section.start_address() as u64));
+            let end_frame = Frame::containing_address(PhysAddr::new(section.end_address() as u64 - 1));
+            for frame in Frame::range_inclusive(start_frame, end_frame) {
+                unsafe {
+                    mapper.identity_map(frame, flags, allocator).expect("Failed to identity map kernel").flush();
+                }
+            }
+        }
+
+    });
+}
+
+struct InactivePageTable {
+    p4_frame: Frame,
+}
+
+impl InactivePageTable {
+    pub fn new(frame: Frame, active_table: & mut RecursivePageTable,
+                                   temporary_page: &mut TemporaryPage) -> InactivePageTable {
+        let table = temporary_page.map_table_frame(frame, active_table);
+        table.zero();
+        table[511].set_frame(frame.clone(), Flags::PRESENT | Flags::WRITABLE);
+        temporary_page.unmap(active_table);
+        InactivePageTable { p4_frame: frame }
+    }
+
+    pub fn under<F>(&mut self, active_table: &mut RecursivePageTable,
+                    temporary_page: &mut TemporaryPage, f: F)
+        where F: FnOnce(&mut RecursivePageTable)
+    {
+        let backup = control::Cr3::read().0;
+        let p4_table = temporary_page.map_table_frame(backup, active_table);
+        unsafe {
+            (*P4)[511].set_frame(self.p4_frame, Flags::PRESENT | Flags::WRITABLE);
+        }
+        x86_64::instructions::tlb::flush_all();
+
+        f(active_table);
+
+        p4_table[511].set_frame(self.p4_frame, Flags::PRESENT | Flags::WRITABLE);
+        x86_64::instructions::tlb::flush_all();
+
+        temporary_page.unmap(active_table);
+    }
+}
+
+pub fn get_active_page_table() -> RecursivePageTable<'static> {
+    unsafe {
+        RecursivePageTable::new(&mut *P4).expect("Could not create Page Table")
+    }
+}
+
 
 pub fn test_paging<A>(allocator: &mut A)
     where A: FrameAllocator<Size4KiB>
 {
-    let mut page_table = unsafe { RecursivePageTable::new(&mut *P4).expect("Could not create Page Table") };
+    let mut page_table = get_active_page_table();
 
     let addr = 42 * 512 * 512 * 4096; // 42th P3 entry
     let page = Page::containing_address(VirtAddr::new(addr));

src/memory/paging/temporary_page.rs

@@ -0,0 +1,34 @@
+use super::{Page, Flags, VirtAddr, RecursivePageTable, Mapper, FrameAllocator, Size4KiB, Frame, PageTable};
+use super::super::frame_allocator::TinyAllocator;
+
+pub struct TemporaryPage {
+    page: Page,
+    allocator: TinyAllocator,
+}
+
+impl TemporaryPage {
+    pub fn new<A>(page: Page, allocator: &mut A) -> TemporaryPage
+        where A: FrameAllocator<Size4KiB>
+    {
+        TemporaryPage {
+            page,
+            allocator: TinyAllocator::new(allocator),
+        }
+    }
+
+    pub fn map(&mut self, frame: Frame, active_table: &mut RecursivePageTable) -> VirtAddr {
+        unsafe {
+            active_table.map_to(self.page, frame, Flags::PRESENT | Flags::WRITABLE, &mut self.allocator).expect("Failed to map temporary page").flush();
+        }
+        self.page.start_address()
+    }
+
+    pub fn unmap(&mut self, active_table: &mut RecursivePageTable) {
+        active_table.unmap(self.page).expect("Failed to unmap").1.flush()
+    }
+
+    pub fn map_table_frame(&mut self, frame: Frame,
+                           active_table: &mut RecursivePageTable) -> &mut PageTable {
+        unsafe { &mut *(self.map(frame, active_table).as_u64() as *mut PageTable) }
+    }
+}