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This instantly creates a page fault as we always map pages with ring 0
permissions.

zion/common/gdt.cpp

@@ -90,3 +90,5 @@ void InitGdt() {
       "ltr %%ax;" ::
           : "rax");
 }
+
+void SetRsp0(uint64_t rsp0) { gTaskStateSegment.rsp0 = rsp0; }

zion/common/gdt.h

@@ -1,3 +1,7 @@
 #pragma once
 
+#include <stdint.h>
+
 void InitGdt();
+
+void SetRsp0(uint64_t rsp0);