From d6c56fb5124707cffa8bbe978249c07b062c25be Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Sun, 13 Nov 2022 16:31:32 +0100
Subject: [PATCH] Mapping finally works!!

---
 kernel/src/arch/x86_64/MMU.cpp | 19 ++++++++++++-------
 kernel/src/main.cpp            | 21 +++++++++++++++------
 2 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/kernel/src/arch/x86_64/MMU.cpp b/kernel/src/arch/x86_64/MMU.cpp
index 1ccc1c08..d79a995a 100644
--- a/kernel/src/arch/x86_64/MMU.cpp
+++ b/kernel/src/arch/x86_64/MMU.cpp
@@ -1,5 +1,6 @@
 #include "arch/MMU.h"
 #include "MemoryManager.h"
+#include "arch/Serial.h"
 #include <String.h>
 
 #define PAGE_SIZE 4096
@@ -23,21 +24,21 @@ struct [[gnu::packed]] PageTableEntry
     u8 available2 : 3;
     bool no_execute : 1;
 
-    void set_address(uint64_t addr);
-    uint64_t get_address();
+    void set_address(u64 addr);
+    u64 get_address();
 };
 
 #pragma GCC push_options
 #pragma GCC diagnostic ignored "-Wconversion"
 
-void PageTableEntry::set_address(uint64_t addr)
+void PageTableEntry::set_address(u64 addr)
 {
     this->address = (addr >> 12);
 }
 
-uint64_t PageTableEntry::get_address()
+u64 PageTableEntry::get_address()
 {
-    return (uint64_t)this->address << 12;
+    return (u64)this->address << 12;
 }
 
 #pragma GCC pop_options
@@ -170,6 +171,7 @@ namespace MMU
             l4.present = true;
             l4.set_address(addr.release_value());
             memset(l3_table(virt), 0, PAGE_SIZE);
+            l4.ignore0 = l4.ignore1 = 0;
         }
         if (flags & Flags::ReadWrite) l4.read_write = true;
         if (flags & Flags::User) l4.user = true;
@@ -182,6 +184,7 @@ namespace MMU
             l3.present = true;
             l3.set_address(addr.release_value());
             memset(l2_table(virt), 0, PAGE_SIZE);
+            l3.ignore0 = l3.ignore1 = 0;
         }
         if (flags & Flags::ReadWrite) l3.read_write = true;
         if (flags & Flags::User) l3.user = true;
@@ -196,6 +199,7 @@ namespace MMU
             l2.present = true;
             l2.set_address(addr.release_value());
             memset(l1_table(virt), 0, PAGE_SIZE);
+            l2.ignore0 = l2.ignore1 = 0;
         }
         if (flags & Flags::ReadWrite) l2.read_write = true;
         if (flags & Flags::User) l2.user = true;
@@ -203,15 +207,16 @@ namespace MMU
         if (l2.larger_pages) return err; // FIXME: Replacing larger pages is not supported ATM
 
         auto& l1 = l1_entry(virt);
-        bool was_present = l1.present;
+        if (l1.present) return err; // Please explicitly unmap the page before mapping it again.
+        l1.ignore0 = l1.ignore1 = false;
         l1.present = true;
         if (flags & Flags::ReadWrite) l1.read_write = true;
         if (flags & Flags::User) l1.user = true;
         if (flags & Flags::WriteThrough) l1.write_through = true;
         if (flags & Flags::CacheDisable) l1.cache_disabled = true;
         if (flags & Flags::NoExecute) l1.no_execute = true;
+        if (l1.ignore0 || l1.ignore1) return {1};
         l1.set_address(phys);
-        if (was_present) flush_page(virt);
         return {};
     }
 
diff --git a/kernel/src/main.cpp b/kernel/src/main.cpp
index 2731e861..4d47e607 100644
--- a/kernel/src/main.cpp
+++ b/kernel/src/main.cpp
@@ -21,30 +21,39 @@ extern "C" void _start()
 
     u64 physical = MemoryManager::alloc_physical_page().release_value();
 
-    bool success = !MMU::map(address, physical, MMU::ReadWrite | MMU::NoExecute).has_error();
+    auto rc = MMU::map(address, physical, MMU::ReadWrite);
+    bool success = !rc.has_error();
+
+    int flags;
+    u8* ptr;
 
     if (success) Serial::println("Mapped page :)");
     else
+    {
         Serial::println("Failed to map page");
+        goto failure;
+    }
 
     if (MMU::get_physical(address).release_value() == physical) Serial::println("Mapping is active ;)");
     else
+    {
         Serial::println("Mapping is not active");
+        goto failure;
+    }
 
-    int flags = MMU::get_flags(address).release_value();
+    flags = MMU::get_flags(address).release_value();
 
     if (flags & MMU::ReadWrite) Serial::println("Mapping is writable");
     if (flags & MMU::NoExecute) Serial::println("Mapping is not executable");
 
-    u32* ptr = (u32*)address;
-    (void)*ptr;
-
-    Serial::println("Can read from pointer");
+    ptr = (u8*)address;
 
     *ptr = 8;
 
     Serial::println("Can write to pointer");
 
+failure:
+
     for (;;)
         ;
 }
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