Resolved page faults from user stacks

zion/memory/user_stack_manager.cpp

@@ -21,3 +21,14 @@ void UserStackManager::FreeUserStack(uint64_t stack_ptr) {
   freed_stacks_++;
   dbgln("%u freed user stacks", freed_stacks_);
 }
+
+bool UserStackManager::IsValidStack(uint64_t vaddr) {
+  if (vaddr < next_stack_ || vaddr > (kStackMax - 0x1000)) {
+    return false;
+  }
+  // Checks if the address is in the first page of the stack.
+  if (vaddr & 0xFF000) {
+    return true;
+  }
+  return false;
+}

zion/memory/user_stack_manager.h

@@ -20,6 +20,9 @@ class UserStackManager {
   uint64_t NewUserStack();
   void FreeUserStack(uint64_t stack_ptr);
 
+  // Used to check if we should page in this address.
+  bool IsValidStack(uint64_t vaddr);
+
  private:
   const uint64_t kStackMax = 0x00008000'00000000;
   const uint64_t kStackMin = 0x00007FF0'00000000;