From 7d57ddef634caaf2fa0225ede98468144a45e4b9 Mon Sep 17 00:00:00 2001
From: Pawel Wieczorkiewicz <wipawel@amazon.de>
Date: Tue, 9 Feb 2021 10:30:27 +0100
Subject: [PATCH] rmode: add spin lock protecting long_to_real CS

Signed-off-by: Pawel Wieczorkiewicz <wipawel@amazon.de>
---
 arch/x86/boot/head.S      | 2 ++
 arch/x86/real_mode_func.c | 5 +++++
 2 files changed, 7 insertions(+)

diff --git a/arch/x86/boot/head.S b/arch/x86/boot/head.S
index d4b42d83..0e3813a7 100644
--- a/arch/x86/boot/head.S
+++ b/arch/x86/boot/head.S
@@ -85,6 +85,8 @@ GLOBAL(_start)
     ljmp  $__KERN_CS64, $.Llong_mode
 
 ENTRY(prot_to_real)
+    /* FIXME: Add spinlock */
+
     lea   (boot_gdt_ptr), %eax
     push  %eax
     lea   (boot_idt_ptr), %eax
diff --git a/arch/x86/real_mode_func.c b/arch/x86/real_mode_func.c
index 985c0767..8a787f6a 100644
--- a/arch/x86/real_mode_func.c
+++ b/arch/x86/real_mode_func.c
@@ -27,17 +27,22 @@
 #include <lib.h>
 #include <percpu.h>
 #include <smp/smp.h>
+#include <spinlock.h>
 #include <traps.h>
 
 extern void _long_to_real(const void *gdt_ptr, const void *idt_ptr);
 
+static spinlock_t lock = SPINLOCK_INIT;
+
 /* FIXME: add real mode calling functionality */
 void long_to_real(void) {
+    spin_lock(&lock);
     percpu_t *percpu = get_percpu_page(smp_processor_id());
 
     dprintk("%s: Before call\n", __func__);
     _long_to_real(&percpu->gdt_ptr, &percpu->idt_ptr);
     dprintk("%s: After call\n", __func__);
+    spin_unlock(&lock);
 }
 
 void init_real_mode(void) { init_rmode_traps(); }