Look for local APIC, try to map it

kernel/src/arch/x86_64/gdt.rs

@@ -9,8 +9,8 @@ use x86_64::structures::gdt;
 use x86_64::structures::gdt::*;
 
 use crate::log::*;
-use crate::{log_info, log_trace};
 use crate::memory::alloc::format;
+use crate::{log_info, log_trace};
 
 #[allow(dead_code)]
 pub trait GdtEntryRead {

kernel/src/arch/x86_64/interrupts.rs

@@ -1,11 +1,19 @@
 // Copyright (c) 2025 shibedrill
 // SPDX-License-Identifier: MIT
 
-use crate::LogLevel;
-use crate::{LOGGER, format, log_trace};
+use crate::{LOGGER, format, log_info, log_trace};
+use crate::{LogLevel, log_error};
 use lazy_static::lazy_static;
+use x86_64::PhysAddr;
 use x86_64::structures::idt::*;
 
+pub fn get_lapic_addr() -> PhysAddr {
+    let apic_base = x86_64::registers::model_specific::ApicBase::read();
+    let addr: PhysAddr = apic_base.0.start_address();
+    log_info!("Found LAPIC at 0x{:x}, flags {:?}", addr, apic_base.1);
+    addr
+}
+
 lazy_static! {
     pub static ref IDT: InterruptDescriptorTable = {
         let mut idt = InterruptDescriptorTable::new();
@@ -14,6 +22,7 @@ lazy_static! {
         // approach will fall apart once multiarch support is re-added.
         idt.double_fault.set_handler_fn(double_fault);
         idt.page_fault.set_handler_fn(page_fault);
+        idt.general_protection_fault.set_handler_fn(gen_prot_fault);
         idt
     };
 }
@@ -37,7 +46,7 @@ extern "x86-interrupt" fn page_fault(info: InterruptStackFrame, errcode: PageFau
     );
     if errcode.contains(PageFaultErrorCode::USER_MODE) {
         // Fault occurred in usermode. Non fatal.
-        todo!()
+        todo!("Page fault handler (usermode)")
     } else {
         // Fault occurred in kernel mode. This is possibly fatal.
         // This is recoverable if we simply hit an unavailable page,
@@ -46,9 +55,20 @@ extern "x86-interrupt" fn page_fault(info: InterruptStackFrame, errcode: PageFau
             | errcode.contains(PageFaultErrorCode::MALFORMED_TABLE)
         {
             let info_formatted = format!("{info:#?}");
-            crate::interrupt::page_fault(addr.unwrap().as_u64() as usize, info_formatted)
+            crate::interrupt::page_fault_fatal(addr.unwrap().as_u64() as usize, info_formatted)
         } else {
-            todo!()
+            log_error!("Page Fault, trying to recover...");
+            todo!("Page fault handler (kernel mode)")
         }
     }
 }
+
+#[allow(dead_code)]
+extern "x86-interrupt" fn gen_prot_fault(info: InterruptStackFrame, _: u64) {
+    crate::interrupt::gen_prot_fault(format!(
+        "RIP 0x{:x}, CS {} ({:?})",
+        info.instruction_pointer,
+        info.code_segment.index(),
+        info.code_segment.rpl()
+    ));
+}

kernel/src/interrupt/mod.rs

@@ -1,12 +1,17 @@
 // Copyright (c) 2025 shibedrill
 // SPDX-License-Identifier: MIT
 
-use crate::memory::alloc::string::String;
+use crate::log::*;
+use crate::{format, log_error, memory::alloc::string::String};
 
 pub fn double_fault(info: String) -> ! {
     panic!("Double fault: {}", info);
 }
 
-pub fn page_fault(addr: usize, info: String) -> ! {
-    panic!("Page fault at 0x{:x}: {}", addr, info);
+pub fn page_fault_fatal(addr: usize, info: String) -> ! {
+    panic!("Fatal page fault at 0x{:x}: {}", addr, info);
+}
+
+pub fn gen_prot_fault(info: String) {
+    log_error!("General protection fault: {}", info);
 }

kernel/src/main.rs

@@ -31,6 +31,7 @@ use limine::firmware::{
     FIRMWARE_TYPE_EFI32, FIRMWARE_TYPE_EFI64, FIRMWARE_TYPE_SBI, FIRMWARE_TYPE_X86BIOS,
 };
 use spin::mutex::Mutex;
+use x86_64::structures::paging::{PageTableFlags, page_table::PageTableEntry};
 
 use crate::{
     arch::{
@@ -38,9 +39,10 @@ use crate::{
         x86_64::{
             cpuid::{CPUID, virt_supported},
             gdt::dump_gdt,
+            interrupts::get_lapic_addr,
         },
     },
-    memory::paging::{self, active_root_table},
+    memory::paging::{self, active_root_table, map_page, phys_to_virt},
 };
 
 lazy_static! {
@@ -147,7 +149,7 @@ unsafe extern "C" fn main() -> ! {
         None => log_info!("Multiprocessing response not received"),
         Some(resp) => {
             log_info!("Multiprocessing response received");
-            log_trace!("{} CPUs found", resp.cpus().len());
+            log_info!("{} CPUs found", resp.cpus().len());
         }
     }
 
@@ -183,11 +185,24 @@ unsafe extern "C" fn main() -> ! {
             root_ptable_info.1,
             addr_of!(*root_ptable_info.0) as usize
         );
+        // This is an expensive function. Only run it if we're actually logging the results.
+        let loglevel = LOGGER.lock().level;
+        if loglevel > LogLevel::Trace {
             paging::walk_tables();
         }
+    }
 
     log_info!("Long mode: {}", asm::long_mode());
     dump_gdt();
 
+    let lapic = get_lapic_addr();
+    let mapping = {
+        let mut m = PageTableEntry::new();
+        m.set_addr(lapic, PageTableFlags::PRESENT);
+        m
+    };
+    let res = map_page(phys_to_virt(lapic), mapping);
+    log_info!("Map status: {:?}", res);
+
     panic!("Finished boot, but cannot start init because processes not implemented!");
 }

kernel/src/memory/mod.rs

@@ -90,16 +90,10 @@ pub fn log_address() {
     if let Some(resp) = ADDRESS_REQUEST.response() {
         log_info!("Kernel physical start address: 0x{:x}", resp.physical_base);
         log_info!("Kernel virtual start address: 0x{:x}", resp.virtual_base);
-        log_info!(
-            "Testing virt_to_phys(): 0x{:x}",
-            resp.virtual_base
-        );
+        log_info!("Testing virt_to_phys(): 0x{:x}", resp.virtual_base);
         let hhdm_vaddr = VirtAddr::new(resp.virtual_base);
         let hhdm_paddr = virt_to_phys(hhdm_vaddr);
-        log_info!(
-            "Result: 0x{:x}",
-            hhdm_paddr.unwrap()
-        );
+        log_info!("Result: 0x{:x}", hhdm_paddr.unwrap());
     } else {
         log_warning!("No kernel address response provided.");
     }

kernel/src/memory/paging.rs

@@ -1,3 +1,4 @@
+use core::ops::DerefMut;
 use core::ops::Index;
 use core::ptr::addr_of;
 
@@ -8,17 +9,83 @@ use x86_64::registers::control;
 use x86_64::registers::control::Cr4Flags;
 use x86_64::structures::paging::PageTable;
 use x86_64::structures::paging::PageTableFlags;
+use x86_64::structures::paging::page_table::PageTableEntry;
 
 use crate::log::*;
 use crate::memory::HHDM_RESPONSE;
 use crate::memory::format;
 
 #[allow(dead_code)]
-pub fn map_page(_virt: VirtAddr, _phys: PhysAddr) {
+pub fn map_page(virt: VirtAddr, mapping: PageTableEntry) -> Option<VirtAddr> {
     // TODO:
     // This function should create necessary page tables until the
     // supplied virtual address maps to the supplied physical address.
-    todo!()
+    // Currently, it *will* give up if there are any missing tables on the path.
+    // It needs to be altered to support creating new intermediary tables.
+    // This will likely not be a necessary function in the future if VMM is left to processes.
+    log_info!(
+        "Mapping 0x{:x} to 0x{:x} with flags {:?}",
+        virt,
+        mapping.addr(),
+        mapping.flags()
+    );
+    let root_table = unsafe { active_root_table() };
+    let mut current_table = root_table;
+    let table_indices = [
+        virt.as_u64().bits(0..=11) as usize,  // Page offset
+        virt.as_u64().bits(12..=20) as usize, // Page Table index
+        virt.as_u64().bits(21..=29) as usize, // Page Directory index
+        virt.as_u64().bits(30..=38) as usize, // Page Directory Pointer Table index
+        virt.as_u64().bits(39..=47) as usize, // Page Map Level 4 index
+        virt.as_u64().bits(48..=56) as usize, // Page Map Level 5 index
+    ];
+    while current_table.1 > 0 {
+        log_trace!(
+            "Searching through a level {} table at 0x{:x}",
+            current_table.1,
+            addr_of!(*current_table.0) as usize
+        );
+        log_trace!("Index: {}", table_indices[current_table.1]);
+        let current_table_entry: &mut PageTableEntry =
+            &mut current_table.0.deref_mut()[table_indices[current_table.1]];
+        if current_table_entry
+            .flags()
+            .contains(PageTableFlags::PRESENT)
+            && !current_table_entry.is_unused()
+        {
+            if current_table_entry
+                .flags()
+                .contains(PageTableFlags::HUGE_PAGE)
+            {
+                if current_table.1 == 3 {
+                    // Huge page (1GiB), last 30 bits preserved
+                    log_error!("Could not map: Entry on path is Huge Page!");
+                    return None;
+                } else if current_table.1 == 2 {
+                    // Large page (2MiB), last 21 bits preserved
+                    log_error!("Could not map: Entry on path is Large Page!");
+                    return None;
+                }
+            } else if current_table.1 > 1 {
+                current_table = (
+                    unsafe { &mut *phys_to_virt(current_table_entry.addr()).as_mut_ptr() }
+                        as &mut PageTable,
+                    current_table.1 - 1,
+                );
+            } else {
+                current_table_entry.set_addr(mapping.addr(), mapping.flags());
+                return Some(virt);
+            }
+        } else {
+            log_error!(
+                "Could not map: Level {} entry on path is not present!",
+                current_table.1
+            );
+            return None;
+        }
+    }
+    // Current table is level 1
+    unreachable!()
 }
 
 #[allow(dead_code)]
@@ -89,7 +156,11 @@ pub fn virt_to_phys(virt: VirtAddr) -> Option<PhysAddr> {
         virt.as_u64().bits(48..=56) as usize, // Page Map Level 5 index
     ];
     while current_table.1 > 0 {
-        log_trace!("Searching through a level {} table at 0x{:x}", current_table.1, addr_of!(*current_table.0) as usize);
+        log_trace!(
+            "Searching through a level {} table at 0x{:x}",
+            current_table.1,
+            addr_of!(*current_table.0) as usize
+        );
         log_trace!("Index: {}", table_indices[current_table.1]);
         let current_table_entry = current_table.0.index(table_indices[current_table.1]);
         if current_table_entry

kernel/src/process.rs

@@ -33,7 +33,7 @@ pub struct Process {
 
 #[allow(dead_code)]
 pub fn context_switch() -> ! {
-    todo!()
+    todo!("Context switch")
 }
 
 #[allow(dead_code)]