kernel: impl buddy physical allocator/pmm

crates/rbtree/src/raw_node.rs

@@ -1,3 +1,4 @@
+use core::fmt::Debug;
 use core::marker::PhantomData;
 use core::mem;
 use core::ops::Not;
@@ -657,6 +658,15 @@ pub struct RBTree<N: UnsafeNode> {
     root: Option<NonNull<N>>,
 }
 
+impl<N: UnsafeNode> Debug for RBTree<N>
+where
+    N::Key: Debug,
+{
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_set().entries(self.iter()).finish()
+    }
+}
+
 impl<N: UnsafeNode> RBTree<N> {
     pub fn new() -> Self {
         Self { root: None }
@@ -1153,7 +1163,9 @@ impl<'a, N: UnsafeNode + 'a> Iterator for TreeIter<'a, N> {
     fn next(&mut self) -> Option<Self::Item> {
         self.range
             .next()
-            .map(|n| unsafe { n.node().unwrap().as_ref().key() })
+            .as_ref()
+            .and_then(Handle::node)
+            .map(|n| unsafe { n.as_ref().key() })
     }
 }
 
@@ -1161,7 +1173,9 @@ impl<'a, N: UnsafeNode + 'a> DoubleEndedIterator for TreeIter<'a, N> {
     fn next_back(&mut self) -> Option<Self::Item> {
         self.range
             .next_back()
-            .map(|n| unsafe { n.node().unwrap().as_ref().key() })
+            .as_ref()
+            .and_then(Handle::node)
+            .map(|n| unsafe { n.as_ref().key() })
     }
 }
 

kernel/.cargo/config.toml

@@ -10,4 +10,4 @@ target = "x86_64-unknown-kernel.json"
 runner = "./run.sh"
 rustflags = [
     "-C", "force-frame-pointers=yes",
-]
+]

kernel/Cargo.toml

@@ -20,6 +20,7 @@ harness = false
 [[test]]
 name = "stack_overflow"
 harness = false
+test = false # currently doesn't work reliably because the stack corrupts something
 
 [dependencies]
 bit_field = "0.10.3"

kernel/src/boot.rs

@@ -100,12 +100,19 @@ const impl Default for MemoryRegion {
 pub struct BootInfo {
     pub hhdm_base: u64,
     pub memory_map: &'static [MemoryRegion],
+    pub executable_file: Option<&'static [u8]>,
 }
 
 pub static BOOT_INFO: OnceLock<BootInfo> = OnceLock::new();
 static mut MEMORY_MAP: [MemoryRegion; 128] = [MemoryRegion::default(); 128];
 
-pub fn init_boot_info<I: Iterator<Item = MemoryRegion>>(hhdm_base: u64, memory_map: I) {
+pub fn init_boot_info<I: Iterator<Item = MemoryRegion>>(
+    hhdm_base: u64,
+    memory_map: I,
+    executable_file: Option<&'static [u8]>,
+) {
+    _ = crate::memory::HHDM_BASE.try_insert(hhdm_base);
+
     BOOT_INFO.initialize(|| {
         for (i, region) in memory_map.enumerate() {
             assert!(i < 128, "Memory map has more than 128 entries");
@@ -117,6 +124,7 @@ pub fn init_boot_info<I: Iterator<Item = MemoryRegion>>(hhdm_base: u64, memory_m
         Ok::<_, !>(BootInfo {
             hhdm_base,
             memory_map: unsafe { (&raw const MEMORY_MAP).as_ref_unchecked() },
+            executable_file,
         })
     });
 }

kernel/src/limine.rs

@@ -1,4 +1,6 @@
-use core::{cell::UnsafeCell, ffi::CStr, fmt::Debug, ptr::NonNull};
+use core::{cell::UnsafeCell, fmt::Debug, ptr::NonNull};
+
+use crate::serial_println;
 
 #[repr(C)]
 pub struct BaseRevision(UnsafeCell<[u64; 3]>);
@@ -326,6 +328,46 @@ impl LimineFile {
     }
 }
 
+#[used]
+#[unsafe(link_section = ".limine_requests_start")]
+static LIMINE_REQUESTS_START: RequestsStartMarker = REQUESTS_START_MARKER;
+
 #[used]
 #[unsafe(link_section = ".limine_requests")]
 pub static EXECUTABLE_FILE_REQUEST: ExecutableFileRequest = ExecutableFileRequest::new();
+
+#[used]
+#[unsafe(link_section = ".limine_requests")]
+pub static LIMINE_BASE_REVISION: BaseRevision = BaseRevision::from_revision(6);
+
+#[used]
+#[unsafe(link_section = ".limine_requests")]
+pub static FRAMEBUFFER_REQUEST: FramebufferRequest = FramebufferRequest::new();
+
+#[used]
+#[unsafe(link_section = ".limine_requests")]
+pub static HHDM_REQUEST: HhdmRequest = HhdmRequest::new();
+
+#[used]
+#[unsafe(link_section = ".limine_requests")]
+pub static MEMMAP_REQUEST: MemMapRequest = MemMapRequest::new();
+
+#[used]
+#[unsafe(link_section = ".limine_requests_end")]
+static LIMINE_REQUESTS_END: RequestsEndMarker = REQUESTS_END_MARKER;
+
+pub fn init_limine_boot_info() {
+    crate::boot::init_boot_info(
+        HHDM_REQUEST
+            .offset()
+            .expect("HHDM offset not provided by bootloader"),
+        MEMMAP_REQUEST
+            .entries()
+            .iter()
+            .inspect(|e| {
+                serial_println!("{e:?}");
+            })
+            .map(|&&e| e.into()),
+        EXECUTABLE_FILE_REQUEST.file().map(|f| f.bytes()),
+    );
+}

kernel/src/main.rs

@@ -23,25 +23,9 @@ static GDT: LazyLock<GlobalDescriptorTable> = LazyLock::new(GlobalDescriptorTabl
 #[unsafe(no_mangle)]
 extern "C" fn _start() -> ! {
     kernel::logger::init(log::LevelFilter::Trace);
-    assert!(limine_requests::LIMINE_BASE_REVISION.is_supported());
+    assert!(kernel::limine::LIMINE_BASE_REVISION.is_supported());
 
-    _ = kernel::memory::HHDM_BASE
-        .try_insert(
-            limine_requests::HHDM_REQUEST
-                .offset()
-                .expect("HHDM offset not provided by bootloader"),
-        )
-        .expect("HHDM offset already set");
-
-    kernel::boot::init_boot_info(
-        limine_requests::HHDM_REQUEST
-            .offset()
-            .expect("HHDM offset not provided by bootloader"),
-        limine_requests::MEMMAP_REQUEST
-            .entries()
-            .iter()
-            .map(|&&e| e.into()),
-    );
+    kernel::limine::init_limine_boot_info();
 
     kernel::serial_println!(
         "HHDM offset: 0x{:#x}",
@@ -50,20 +34,19 @@ extern "C" fn _start() -> ! {
 
     kernel::serial_println!(
         "Memory map: {:#?}",
-        limine_requests::MEMMAP_REQUEST.entries()
+        kernel::limine::MEMMAP_REQUEST.entries()
     );
 
     GDT.load();
     IDT.load();
 
-
     kernel::serial_println!("entry point: 0x{:x}", _start as *const () as usize);
     kernel::serial_println!(
         "entry point phy: {:?}",
         kernel::x86_64::paging::get_physical_addr(VirtAddr(_start as *const () as u64))
     );
 
-    let pmm = kernel::memory::PhysicalMemoryAllocator::from_memory_map(
+    let pmm = kernel::memory::PhysicalMemoryManager::from_memory_map(
         kernel::boot::BOOT_INFO
             .get()
             .expect("Boot info not initialized")
@@ -75,7 +58,7 @@ extern "C" fn _start() -> ! {
 
     kernel::serial_println!("PMM: {pmm:#?}");
 
-    let fb = limine_requests::FRAMEBUFFER_REQUEST
+    let fb = kernel::limine::FRAMEBUFFER_REQUEST
         .framebuffers()
         .first()
         .expect("No framebuffer found");
@@ -95,34 +78,3 @@ extern "C" fn _start() -> ! {
 
     kernel::x86_64::halt_loop()
 }
-
-mod limine_requests {
-    use kernel::limine::{
-        BaseRevision, FramebufferRequest, REQUESTS_END_MARKER, REQUESTS_START_MARKER,
-        RequestsEndMarker, RequestsStartMarker,
-    };
-
-    #[used]
-    #[unsafe(link_section = ".limine_requests_start")]
-    static LIMINE_REQUESTS_START: RequestsStartMarker = REQUESTS_START_MARKER;
-
-    #[used]
-    #[unsafe(link_section = ".limine_requests")]
-    pub static LIMINE_BASE_REVISION: BaseRevision = BaseRevision::from_revision(6);
-
-    #[used]
-    #[unsafe(link_section = ".limine_requests")]
-    pub static FRAMEBUFFER_REQUEST: FramebufferRequest = FramebufferRequest::new();
-
-    #[used]
-    #[unsafe(link_section = ".limine_requests")]
-    pub static HHDM_REQUEST: kernel::limine::HhdmRequest = kernel::limine::HhdmRequest::new();
-
-    #[used]
-    #[unsafe(link_section = ".limine_requests")]
-    pub static MEMMAP_REQUEST: kernel::limine::MemMapRequest = kernel::limine::MemMapRequest::new();
-
-    #[used]
-    #[unsafe(link_section = ".limine_requests_end")]
-    static LIMINE_REQUESTS_END: RequestsEndMarker = REQUESTS_END_MARKER;
-}

kernel/src/memory.rs

@@ -1,4 +1,10 @@
-use core::{alloc::Allocator, cell::Cell, fmt::Debug, num::NonZeroUsize, ptr::NonNull};
+use core::{
+    alloc::Allocator,
+    cell::Cell,
+    fmt::Debug,
+    num::{NonZero, NonZeroUsize},
+    ptr::NonNull,
+};
 
 use bit_field::BitField;
 use rbtree::RBTree;
@@ -9,6 +15,8 @@ pub static HHDM_BASE: OnceLock<u64> = OnceLock::new();
 
 pub trait VirtAddrTranslationExt: Sized {
     fn into_phy_addr(self) -> Option<PhyAddr>;
+
+    #[expect(clippy::wrong_self_convention)]
     fn is_mapped(self) -> bool {
         self.into_phy_addr().is_some()
     }
@@ -129,7 +137,118 @@ pub struct PhysicalMemoryManager {
     ///
     /// When a range of pages is freed, we try to locate its buddy and merge
     /// them into a larger chunk recursively.
-    buddies: [u64; 40],
+    buddies: [RBTree<PhysicalPageNode>; 40],
+}
+
+impl Debug for PhysicalMemoryManager {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_struct("PhysicalMemoryManager")
+            .field_with("buddies", |f| {
+                f.debug_list()
+                    .entries(self.buddies.iter().enumerate().map(|(i, tree)| {
+                        struct BuddyDbg<'a> {
+                            index: usize,
+                            tree: &'a RBTree<PhysicalPageNode>,
+                        }
+                        impl Debug for BuddyDbg<'_> {
+                            fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+                                write!(f, "{:#x}: {:?}", 1u64 << self.index, self.tree)
+                            }
+                        }
+                        BuddyDbg { index: i, tree }
+                    }))
+                    .finish()
+            })
+            .finish()
+    }
+}
+
+impl PhysicalMemoryManager {
+    pub fn from_memory_map(memory_map: &[crate::boot::MemoryRegion]) -> Self {
+        let usable_regions = memory_map
+            .iter()
+            .filter(|region| region.region_type.is_usable());
+
+        let buddies = [(); 40].map(|_| RBTree::default());
+
+        let mut pmm = PhysicalMemoryManager { buddies };
+
+        usable_regions.for_each(|region| {
+            let idx = region.start / crate::x86_64::PAGE_SIZE as u64;
+            let count = region.length / crate::x86_64::PAGE_SIZE as u64;
+
+            pmm.free_region(idx as usize, count as usize);
+        });
+
+        pmm
+    }
+
+    fn free_region(&mut self, page_index: usize, mut count: usize) {
+        serial_println!(
+            "Freeing region: page_index = {:#x}, count = {:#x}",
+            page_index,
+            count
+        );
+        while let Some(bit) = NonZero::new(count.isolate_lowest_one()).map(NonZero::get) {
+            count -= bit;
+
+            let mut bin = bit.trailing_zeros() as usize;
+
+            let mut index = page_index + count;
+            let mut buddy: NonNull<PhysicalPageNode>;
+            loop {
+                // each bin corresponds to a power-of-two number of pages.
+                // each chunk of pages has a buddy that is the same size (in the same bin)
+
+                // for example, the chunk [0, 4) has a buddy [4, 8).
+                let buddy_index = if index & bit == 0 {
+                    // if the chunk is aligned to the size of the chunk, its buddy
+                    // is located at page_index + bit.
+                    index + bit
+                } else {
+                    // if the chunk is not aligned to the size of the chunk, its
+                    // buddy is located at page_index - bit.
+                    index - bit
+                };
+
+                serial_println!(
+                    "looking for buddy: page_index = {:#x}, buddy_index = {:#x}, bin = {}",
+                    index,
+                    buddy_index,
+                    bin
+                );
+
+                match self.buddies[bin].remove(PhysicalPageNodeKey::from_page_index(buddy_index)) {
+                    Some(chunk) => {
+                        serial_println!(
+                            "found buddy: page_index = {:#x}, buddy_index = {:#x}, bin = {}",
+                            index,
+                            buddy_index,
+                            bin
+                        );
+                        buddy = chunk;
+                        index = PhysicalPageNode::page_index(buddy).min(index);
+                        bin += 1;
+                    }
+                    None => break,
+                }
+            }
+
+            let node_ptr = PhysicalPageNode::new_from_page_index(index);
+            serial_println!(
+                "inserting node: page_index = {:#x}, size = {:#x}, bin = {}",
+                index,
+                bit,
+                bin
+            );
+            let None = self.buddies[bin].insert_node(node_ptr) else {
+                panic!(
+                    "Attempted to free a region that is already free: page_index = {}, count = {}",
+                    page_index, bit
+                )
+            };
+        }
+    }
 }
 
 pub struct PhysicalMemoryAllocator {
@@ -699,6 +818,27 @@ impl Debug for PhysicalPageNode {
 }
 
 impl PhysicalPageNode {
+    fn phy(&self) -> Option<PhyAddr> {
+        PhyAddr::from_hhdm_virt(self)
+    }
+
+    fn page_index(this: NonNull<Self>) -> usize {
+        let phy = PhyAddr::from_hhdm_virt(VirtAddr::from(this));
+        phy.expect("PhysicalPageNode is not in HHDM").page_index() as usize
+    }
+
+    fn new_from_page_index(page_index: usize) -> NonNull<Self> {
+        let phy = PhyAddr::from_page_index(page_index);
+        let virt = phy.as_hhdm_virt();
+        let ptr = virt.as_mut::<Self>();
+
+        unsafe {
+            ptr.write(Self::new_red());
+        }
+
+        NonNull::new(ptr).unwrap()
+    }
+
     fn new_red() -> Self {
         PhysicalPageNode(Cell::new(1 << 120))
     }
@@ -757,6 +897,26 @@ impl PhysicalPageNode {
 /// the key does not require any additional bits.
 struct PhysicalPageNodeKey;
 
+impl Debug for PhysicalPageNodeKey {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(f, "{:?}", self.phy())
+    }
+}
+
+impl PhysicalPageNodeKey {
+    fn from_page_index(page_index: usize) -> &'static Self {
+        let phy = PhyAddr::from_page_index(page_index);
+        let virt = phy.as_hhdm_virt();
+        let ptr = virt.as_ptr::<Self>();
+
+        unsafe { &*ptr }
+    }
+
+    fn phy(&self) -> Option<PhyAddr> {
+        PhyAddr::from_hhdm_virt(self)
+    }
+}
+
 impl Eq for PhysicalPageNodeKey {}
 
 impl PartialEq for PhysicalPageNodeKey {

kernel/src/x86_64/backtrace.rs

@@ -1,4 +1,5 @@
-use core::ffi::{CStr, c_void};
+#![allow(dead_code)]
+use core::ffi::c_void;
 
 use crate::{
     limine::LimineFile,
@@ -336,12 +337,10 @@ impl Elf64Sym {
             if let Some(bytes) = crate::limine::EXECUTABLE_FILE_REQUEST
                 .file()
                 .map(LimineFile::bytes)
+                && let Ok(ehdr) = plain::from_bytes::<Elf64Ehdr>(bytes)
+                && let Some(symtab) = ehdr.symtab(bytes)
             {
-                if let Ok(ehdr) = plain::from_bytes::<Elf64Ehdr>(bytes) {
-                    if let Some(symtab) = ehdr.symtab(bytes) {
-                        return symtab;
-                    }
-                }
+                return symtab;
             }
             &[]
         });
@@ -375,6 +374,7 @@ impl Elf64Sym {
             _ => panic!("Invalid bind value"),
         }
     }
+
     fn kind(&self) -> Elf64SymType {
         match self.info & 0xf {
             0 => Elf64SymType::Notype,

kernel/src/x86_64/gdt.rs

@@ -1,7 +1,7 @@
 use core::{
     arch::asm,
     fmt::Debug,
-    mem::offset_of,
+    mem::{MaybeUninit, offset_of},
     ops::{Deref, DerefMut},
 };
 
@@ -468,16 +468,44 @@ impl DerefMut for TssEntry {
     }
 }
 
+const PRIVILEGE_STACK_TABLE_SIZE: usize = 3;
+const INTERRUPT_STACK_TABLE_SIZE: usize = 7;
+
 #[repr(C, packed(4))]
 pub struct TaskStateSegment {
     _reserved1: [u8; 4],
-    pub privilege_stack_table: [u64; 3],
+    pub privilege_stack_table: [u64; PRIVILEGE_STACK_TABLE_SIZE],
     _reserved2: [u8; 8],
-    pub interrupt_stack_table: [u64; 7],
+    pub interrupt_stack_table: [u64; INTERRUPT_STACK_TABLE_SIZE],
     _reserved3: [u8; 10],
     pub iomap_base: u16,
 }
 
+impl Debug for TaskStateSegment {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        let mut dbg = f.debug_struct("TaskStateSegment");
+
+        let rsps = self.privilege_stack_table;
+        let ists = self.interrupt_stack_table;
+
+        dbg.field("RSP0", &format_args!("{:#x}", rsps[0]))
+            .field("RSP1", &format_args!("{:#x}", rsps[1]))
+            .field("RSP2", &format_args!("{:#x}", rsps[2]));
+
+        dbg.field("IST1", &format_args!("{:#x}", ists[0]))
+            .field("IST2", &format_args!("{:#x}", ists[1]))
+            .field("IST3", &format_args!("{:#x}", ists[2]))
+            .field("IST4", &format_args!("{:#x}", ists[3]))
+            .field("IST5", &format_args!("{:#x}", ists[4]))
+            .field("IST6", &format_args!("{:#x}", ists[5]))
+            .field("IST7", &format_args!("{:#x}", ists[6]));
+
+        dbg.field("iomap_base", &format_args!("{:#x}", self.iomap_base));
+
+        dbg.finish()
+    }
+}
+
 impl TaskStateSegment {
     pub const fn new() -> Self {
         Self {
@@ -489,6 +517,13 @@ impl TaskStateSegment {
             _reserved3: [0; 10],
         }
     }
+    pub fn set_stack(&mut self, index: u8, stack: &'static Stack) {
+        assert!(
+            (index as usize) < INTERRUPT_STACK_TABLE_SIZE,
+            "Interrupt stack table index out of bounds"
+        );
+        self.interrupt_stack_table[index as usize] = stack.top().to_address();
+    }
 }
 
 const impl Default for TaskStateSegment {
@@ -500,17 +535,39 @@ const impl Default for TaskStateSegment {
 pub const DF_STACK: u8 = 0;
 pub const NMI_STACK: u8 = 1;
 pub const MC_STACK: u8 = 2;
+pub const PF_STACK: u8 = 3;
+
+const STACK_SIZE: usize = super::PAGE_SIZE * 5;
+#[repr(align(4096))]
+pub struct Stack {
+    _bytes: MaybeUninit<[u8; STACK_SIZE]>,
+}
+
+impl Stack {
+    const fn new() -> Self {
+        Stack {
+            _bytes: MaybeUninit::uninit(),
+        }
+    }
+    fn top(&self) -> *const u8 {
+        unsafe {
+            (&raw const *self)
+                .cast::<u8>()
+                .byte_add(super::PAGE_SIZE * 5)
+        }
+    }
+}
 
 pub static TSS: LazyLock<TaskStateSegment> = LazyLock::new(|| {
     let mut tss = TaskStateSegment::new();
-    const STACK_SIZE: usize = super::PAGE_SIZE * 5;
-    static mut STACKS: [[u8; STACK_SIZE]; 3] = [[0; STACK_SIZE]; 3];
+    static mut STACKS: [Stack; 4] = [const { Stack::new() }; 4];
 
-    let stack_top = |n: usize| unsafe { STACKS[n].as_ptr().add(STACK_SIZE).to_address() };
+    tss.set_stack(DF_STACK, unsafe { &STACKS[DF_STACK as usize] });
+    tss.set_stack(NMI_STACK, unsafe { &STACKS[NMI_STACK as usize] });
+    tss.set_stack(MC_STACK, unsafe { &STACKS[MC_STACK as usize] });
+    tss.set_stack(PF_STACK, unsafe { &STACKS[PF_STACK as usize] });
 
-    tss.interrupt_stack_table[DF_STACK as usize] = stack_top(DF_STACK as usize);
-    tss.interrupt_stack_table[NMI_STACK as usize] = stack_top(NMI_STACK as usize);
-    tss.interrupt_stack_table[MC_STACK as usize] = stack_top(MC_STACK as usize);
+    serial_println!("Initialized TSS {:#?}", tss);
 
     tss
 });

kernel/src/x86_64/idt.rs

@@ -89,6 +89,9 @@ impl Entry {
             ExceptionVector::NON_MASKABLE_INTERRUPT => {
                 options.set_interrupt_stack_table_index(super::gdt::NMI_STACK);
             }
+            ExceptionVector::PAGE_FAULT => {
+                options.set_interrupt_stack_table_index(super::gdt::PF_STACK);
+            }
             ExceptionVector::MACHINE_CHECK => {
                 options.set_interrupt_stack_table_index(super::gdt::MC_STACK);
             }
@@ -520,7 +523,12 @@ extern "C" fn global_interrupt_handler(
             serial_println!("Breakpoint interrupt handled successfully.");
         }
         ExceptionVector::PAGE_FAULT => {
-            serial_println!("Page fault occurred! Error code: {:#x}", error_code);
+            let cr2 = super::registers::Cr2::read();
+            serial_println!(
+                "Page fault occurred! Error code: {:#x} CR2: {:#x}",
+                error_code,
+                cr2.0
+            );
             debug_backtrace(&Context {
                 rip: frame.instruction_pointer,
                 registers: *registers,

kernel/src/x86_64/registers.rs

@@ -64,6 +64,17 @@ bitflags::bitflags! {
     }
 }
 
+pub struct Cr2(pub u64);
+impl Cr2 {
+    pub fn read() -> Self {
+        let value: u64;
+        unsafe {
+            asm!("mov {}, cr2", out(reg) value, options(nomem, nostack, preserves_flags));
+        }
+        Self(value)
+    }
+}
+
 impl Cr4 {
     pub fn read() -> Self {
         let value: u64;

kernel/tests/stack_overflow.rs

@@ -5,6 +5,7 @@
 use core::{cell::UnsafeCell, mem::offset_of};
 
 use kernel::{
+    serial_println,
     sync::LazyLock,
     x86_64::{
         gdt::{DF_STACK, GlobalDescriptorTable, RING0},
@@ -17,6 +18,7 @@ pub static GDT: LazyLock<GlobalDescriptorTable> = LazyLock::new(GlobalDescriptor
 #[unsafe(export_name = "_start")]
 pub extern "C" fn main() -> ! {
     kernel::serial_println!("Hello, world!");
+    kernel::limine::init_limine_boot_info();
 
     GDT.load();
     kernel::serial_println!("[ok] GDT loaded");
@@ -25,12 +27,13 @@ pub extern "C" fn main() -> ! {
         _stack_frame: &mut idt::InterruptStackFrame,
         _error_code: u64,
     ) -> ! {
-        kernel::serial_println!("[ok] Double fault handler called");
+        kernel::serial_println!("[ok] Fault handler called");
         kernel::testing::exit_qemu(kernel::testing::QemuExitCode::Success)
     }
 
     static IDT: LazyLock<InterruptDescriptorTable> = LazyLock::new(|| {
         let mut idt = InterruptDescriptorTable::new_default();
+
         idt.double_fault = unsafe {
             Entry::new(
                 double_fault_handler as *const (),
@@ -38,7 +41,19 @@ pub extern "C" fn main() -> ! {
                 idt::EntryOptions::empty_interrupt_gate()
                     .with_present(true)
                     .with_privilege_level(RING0)
-                    .with_interrupt_stack_table_index(DF_STACK),
+                    .with_interrupt_stack_table_index(kernel::x86_64::gdt::DF_STACK),
+            )
+        };
+
+        // this should fire #PF since we have it installed anways in the default idt
+        idt.page_fault = unsafe {
+            Entry::new(
+                double_fault_handler as *const (),
+                offset_of!(GlobalDescriptorTable, kernel_code) as u16,
+                idt::EntryOptions::empty_interrupt_gate()
+                    .with_present(true)
+                    .with_privilege_level(RING0)
+                    .with_interrupt_stack_table_index(kernel::x86_64::gdt::PF_STACK),
             )
         };