From a34f179d8455ae6627da858bfbf549b488149a11 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20Gr=C3=A9goire?= <loic@gregoire.dev>
Date: Tue, 14 Apr 2026 22:21:36 -0400
Subject: [PATCH] refactor(amd64): rework MSR handling

---
 src/arch/amd64/root.zig     | 26 ++++++++++++++++++++++----
 src/kern/amd64/init.zig     |  2 +-
 src/platform/pc/pvclock.zig |  2 +-
 3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/src/arch/amd64/root.zig b/src/arch/amd64/root.zig
index f1629ab..fa34bca 100644
--- a/src/arch/amd64/root.zig
+++ b/src/arch/amd64/root.zig
@@ -6,6 +6,7 @@ pub const name = "amd64";
 pub const Msr = enum(u32) {
     /// IA32_APIC_BASE
     LapicBase = 0x1B,
+    X2ApicBase = 0x800,
     /// IA32_FS_BASE
     FsBase = 0xC000_0100,
     /// IA32_GS_BASE
@@ -20,6 +21,7 @@ pub const Msr = enum(u32) {
     LStar = 0xC000_0082,
     /// MSR_KVM_SYSTEM_TIME_NEW
     KvmSystemTimeNew = 0x4B564D01,
+    _,
 };
 
 pub const IrqFrame = extern struct {
@@ -92,26 +94,34 @@ pub inline fn inl(port: u16) u32 {
     );
 }
 
-pub inline fn rdmsr(msr: Msr) u64 {
+pub inline fn rdmsr(msr: u32) u64 {
     var low: u32 = undefined;
     var high: u32 = undefined;
     asm volatile ("rdmsr"
         : [low] "={eax}" (low),
           [high] "={edx}" (high),
-        : [msr] "{ecx}" (@intFromEnum(msr)),
+        : [msr] "{ecx}" (msr),
     );
     return @as(u64, high) << 32 | low;
 }
 
-pub inline fn wrmsr(msr: Msr, value: u64) void {
+pub inline fn wrmsr(msr: u32, value: u64) void {
     asm volatile ("wrmsr"
         :
         : [low] "{eax}" (@as(u32, @truncate(value))),
           [high] "{edx}" (@as(u32, @truncate(value >> 32))),
-          [msr] "{ecx}" (@intFromEnum(msr)),
+          [msr] "{ecx}" (msr),
     );
 }
 
+pub inline fn read_msr(comptime msr: Msr) u64 {
+    return rdmsr(@intFromEnum(msr));
+}
+
+pub inline fn write_msr(comptime msr: Msr, value: u64) void {
+    wrmsr(@intFromEnum(msr), value);
+}
+
 pub inline fn rdgsbase() usize {
     return asm volatile ("rdgsbase %[ret]"
         : [ret] "=r" (-> usize),
@@ -630,6 +640,14 @@ pub const Idtr = extern struct {
     base: usize align(1),
 };
 
+pub fn sidtr() Idtr {
+    var idtr: Idtr = undefined;
+    asm volatile ("sidt %[idtr]"
+        : [idtr] "={memory}" (idtr),
+    );
+    return idtr;
+}
+
 pub const IdtEntry = extern struct {
     offset_low: u16 align(1),
     selector: u16 align(1),
diff --git a/src/kern/amd64/init.zig b/src/kern/amd64/init.zig
index bd9c7a7..4f3837e 100644
--- a/src/kern/amd64/init.zig
+++ b/src/kern/amd64/init.zig
@@ -34,5 +34,5 @@ pub fn early_init() linksection(b.init) void {
     int.init();
 
     // Enable Per-CPU data for this CPU
-    amd64.wrmsr(.GsBase, 0);
+    amd64.write_msr(.GsBase, 0);
 }
diff --git a/src/platform/pc/pvclock.zig b/src/platform/pc/pvclock.zig
index 2ebb0cd..50bf77a 100644
--- a/src/platform/pc/pvclock.zig
+++ b/src/platform/pc/pvclock.zig
@@ -33,7 +33,7 @@ pub fn init() linksection(b.init) void {
     const page = mm.phys.alloc();
     pvclock = @ptrFromInt(mm.p2v(page));
 
-    amd64.wrmsr(.KvmSystemTimeNew, page | 1);
+    amd64.write_msr(.KvmSystemTimeNew, page | 1);
 
     time_at_boot = read_pvclock();