From 72885190e9bdf63995bc565d5315cf8e62e187a8 Mon Sep 17 00:00:00 2001
From: Drew Galbraith <dgalbraith33@gmail.com>
Date: Mon, 12 Jun 2023 23:28:23 -0700
Subject: [PATCH] Resolved page faults from user stacks

---
 zion/memory/user_stack_manager.cpp | 11 +++++++++++
 zion/memory/user_stack_manager.h   |  3 +++
 zion/object/address_space.cpp      |  5 +++++
 3 files changed, 19 insertions(+)

diff --git a/zion/memory/user_stack_manager.cpp b/zion/memory/user_stack_manager.cpp
index b6f1dc2..6a38b1c 100644
--- a/zion/memory/user_stack_manager.cpp
+++ b/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;
+}
diff --git a/zion/memory/user_stack_manager.h b/zion/memory/user_stack_manager.h
index ebd47bf..5ed7a0f 100644
--- a/zion/memory/user_stack_manager.h
+++ b/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;
diff --git a/zion/object/address_space.cpp b/zion/object/address_space.cpp
index 2ee374e..0faa89f 100644
--- a/zion/object/address_space.cpp
+++ b/zion/object/address_space.cpp
@@ -55,6 +55,11 @@ bool AddressSpace::HandlePageFault(uint64_t vaddr) {
 #if K_VMAS_DEBUG
   dbgln("[VMAS] Page Fault!");
 #endif
+  if (user_stacks_.IsValidStack(vaddr)) {
+    MapPage(cr3_, vaddr, phys_mem::AllocatePage());
+    return true;
+  }
+
   MemoryMapping* mapping = GetMemoryMappingForAddr(vaddr);
   if (mapping == nullptr) {
     return false;