From c9a7d501b2e4cecf9635aa4a56a536ff058f8bf9 Mon Sep 17 00:00:00 2001
From: Ruihan Li <lrh2000@pku.edu.cn>
Date: Fri, 18 Apr 2025 12:29:26 +0800
Subject: [PATCH] Rewrite `trap/idt.rs`

---
 ostd/src/arch/x86/trap/idt.rs | 87 +++++++++++++++++++++--------------
 ostd/src/arch/x86/trap/mod.rs |  2 +-
 2 files changed, 54 insertions(+), 35 deletions(-)

diff --git a/ostd/src/arch/x86/trap/idt.rs b/ostd/src/arch/x86/trap/idt.rs
index bb3a584d..ed367dc6 100644
--- a/ostd/src/arch/x86/trap/idt.rs
+++ b/ostd/src/arch/x86/trap/idt.rs
@@ -1,47 +1,66 @@
-// SPDX-License-Identifier: MPL-2.0 OR MIT
-//
-// The original source code is from [trapframe-rs](https://github.com/rcore-os/trapframe-rs),
-// which is released under the following license:
-//
-// SPDX-License-Identifier: MIT
-//
-// Copyright (c) 2020 - 2024 Runji Wang
-//
-// We make the following new changes:
-// * Include `trap.S` in this file and remove unused function `sidt`.
-// * Link `VECTORS` to `trap_handler_table` defined in `trap.S`.
-//
-// These changes are released under the following license:
-//
 // SPDX-License-Identifier: MPL-2.0
 
-//! Configure Interrupt Descriptor Table (GDT).
+//! Configure the Interrupt Descriptor Table (IDT).
 
 use alloc::boxed::Box;
 use core::arch::global_asm;
 
+use spin::Once;
 use x86_64::{
-    structures::idt::{Entry, HandlerFunc, InterruptDescriptorTable},
-    PrivilegeLevel,
+    instructions::tables::lidt,
+    structures::{idt::Entry, DescriptorTablePointer},
+    PrivilegeLevel, VirtAddr,
 };
 
 global_asm!(include_str!("trap.S"));
 
-pub fn init() {
-    extern "C" {
-        #[link_name = "trap_handler_table"]
-        static VECTORS: [HandlerFunc; 256];
-    }
+const NUM_INTERRUPTS: usize = 256;
 
-    let idt = Box::leak(Box::new(InterruptDescriptorTable::new()));
-    let entries: &'static mut [Entry<HandlerFunc>; 256] =
-        unsafe { core::mem::transmute_copy(&idt) };
-    for i in 0..256 {
-        let opt = unsafe { entries[i].set_handler_fn(VECTORS[i]) };
-        // Enable user space `int3` and `into`.
-        if i == 3 || i == 4 {
-            opt.set_privilege_level(PrivilegeLevel::Ring3);
-        }
-    }
-    idt.load();
+extern "C" {
+    #[link_name = "trap_handler_table"]
+    static VECTORS: [usize; NUM_INTERRUPTS];
+}
+
+static GLOBAL_IDT: Once<&'static [Entry<()>]> = Once::new();
+
+/// Initializes and loads the IDT.
+///
+/// The caller should only call this method once in the boot context for each available processor.
+/// This is not a safety requirement, however, because calling this method again will do nothing
+/// more than load the same IDT.
+pub(super) fn init() {
+    let idt = *GLOBAL_IDT.call_once(|| {
+        let idt = Box::leak(Box::new([const { Entry::missing() }; NUM_INTERRUPTS]));
+
+        // SAFETY: The vector array is properly initialized, lives for `'static`, and will never be
+        // mutated. So it's always fine to create an immutable borrow to it.
+        let vectors = unsafe { &VECTORS };
+
+        // Initialize the IDT entries.
+        for (intr_no, &handler) in vectors.iter().enumerate() {
+            let handler = VirtAddr::new(handler as u64);
+
+            let entry = &mut idt[intr_no];
+            // SAFETY: The handler defined in `trap.S` has a correct signature to handle the
+            // corresponding exception or interrupt.
+            let opt = unsafe { entry.set_handler_addr(handler) };
+
+            // Enable `int3` and `into` in the userspace.
+            if intr_no == 3 || intr_no == 4 {
+                opt.set_privilege_level(PrivilegeLevel::Ring3);
+            }
+        }
+
+        idt
+    });
+
+    let idtr = DescriptorTablePointer {
+        limit: (core::mem::size_of_val(idt) - 1) as u16,
+        base: VirtAddr::new(idt.as_ptr().addr() as u64),
+    };
+    // SAFETY: The IDT is valid to load because:
+    //  - It lives for `'static`.
+    //  - It contains correct entries at correct indexes: all handlers are defined in `trap.S` with
+    //    correct handler signatures.
+    unsafe { lidt(&idtr) };
 }
diff --git a/ostd/src/arch/x86/trap/mod.rs b/ostd/src/arch/x86/trap/mod.rs
index 8031ab90..37cfce98 100644
--- a/ostd/src/arch/x86/trap/mod.rs
+++ b/ostd/src/arch/x86/trap/mod.rs
@@ -107,7 +107,7 @@ pub struct TrapFrame {
 /// This function will:
 /// - Switch to a new, CPU-local [GDT].
 /// - Switch to a new, CPU-local [TSS].
-/// - Switch to a new, CPU-local [IDT].
+/// - Switch to a new, global [IDT].
 /// - Enable the [`syscall`] instruction.
 ///
 /// [GDT]: https://wiki.osdev.org/GDT