From d6d40e9ecf2aff5b1e265d26f7651e8633eddabd Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Wed, 19 Nov 2025 19:00:55 -0500
Subject: kern/amd64: mp: Load per-core GDT/IDT

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/arch/amd64/cpu/mp.c  | 15 +++++++++++++++
 sys/inc/arch/amd64/gdt.h | 17 +++++++++++++++++
 sys/inc/mu/cpu.h         |  7 ++++++-
 3 files changed, 38 insertions(+), 1 deletion(-)

(limited to 'sys')

diff --git a/sys/arch/amd64/cpu/mp.c b/sys/arch/amd64/cpu/mp.c
index 1fdc9f7..6911a49 100644
--- a/sys/arch/amd64/cpu/mp.c
+++ b/sys/arch/amd64/cpu/mp.c
@@ -105,6 +105,9 @@ struct mtrr_save {
     uintptr_t physmask[256];
 } mtrr_save;
 
+extern struct gdtr GDTR;
+extern void idt_load(void);
+
 static struct cpu_info *cpu_list[MAX_CPUS];
 static struct ap_bootspace bs;
 static volatile size_t ap_sync = 0;
@@ -293,6 +296,18 @@ cpu_lm_entry(void)
     atomic_inc_int(&aps_up);
     cpu_list[aps_up] = ci;
 
+    /* Initialize the GDT */
+    memcpy(ci->ap_gdt, (void *)GDTR.offset, GDTR.limit);
+    ci->ap_gdtr.offset = (uintptr_t)&ci->ap_gdt[0];
+    ci->ap_gdtr.limit = GDTR.limit;
+    __asmv(
+        "lgdt %0"
+        :
+        : "m" (ci->ap_gdtr)
+        : "memory"
+    );
+
+    idt_load();
     cpu_idle();
     __builtin_unreachable();
 }
diff --git a/sys/inc/arch/amd64/gdt.h b/sys/inc/arch/amd64/gdt.h
index dacfbda..291ab3c 100644
--- a/sys/inc/arch/amd64/gdt.h
+++ b/sys/inc/arch/amd64/gdt.h
@@ -30,9 +30,26 @@
 #ifndef _MACHINE_GDT_H_
 #define _MACHINE_GDT_H_
 
+#include <sys/types.h>
+#include <sys/cdefs.h>
+
 #define GDT_KERNCODE 0x08
 #define GDT_KERNDATA 0x10
 #define GDT_USERCODE 0x18
 #define GDT_USERDATA 0x20
 
+struct __packed gdt_entry {
+    uint16_t limit;
+    uint16_t base_low;
+    uint8_t base_mid;
+    uint8_t access;
+    uint8_t granularity;
+    uint8_t base_hi;
+};
+
+struct __packed gdtr {
+    uint16_t limit;
+    uintptr_t offset;
+};
+
 #endif  /* !_MACHINE_GDT_H_ */
diff --git a/sys/inc/mu/cpu.h b/sys/inc/mu/cpu.h
index 288ba9e..524e42a 100644
--- a/sys/inc/mu/cpu.h
+++ b/sys/inc/mu/cpu.h
@@ -33,7 +33,8 @@
 #include <sys/queue.h>
 #include <sys/types.h>
 #include <os/process.h>
-#include <md/mcb.h>
+#include <md/mcb.h> /* shared */
+#include <md/gdt.h> /* shared */
 
 /*
  * Processor descriptor
@@ -41,12 +42,16 @@
  * @id: Logical ID of the processor
  * @mcb: Machine core block
  * @curproc: Current process
+ * @ap_gdt: GDT for APs [unused for BSP]
+ * @ap_gdtr: GDTR for APs [unused for BSP]
  * @pqueue: Process queue
  */
 struct cpu_info {
     uint8_t id;
     struct mcb mcb;
     struct process *curproc;
+    struct gdt_entry ap_gdt[256];
+    struct gdtr ap_gdtr;
     TAILQ_HEAD(, process) pqueue;
 };
 
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