From 301ad897839d867e017f6cb866f5eb0271e71683 Mon Sep 17 00:00:00 2001
From: Bananymous <bananymousosq@gmail.com>
Date: Thu, 12 Jan 2023 13:45:01 +0200
Subject: [PATCH] Kernel: Unallocate RSDT after we are done with it

---
 kernel/arch/i386/APIC.cpp   |  5 +++--
 kernel/arch/i386/MMU.cpp    | 27 +++++++++++++++++++++++++++
 kernel/include/kernel/MMU.h |  5 ++++-
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/kernel/arch/i386/APIC.cpp b/kernel/arch/i386/APIC.cpp
index 57860f4446..c426ee9d28 100644
--- a/kernel/arch/i386/APIC.cpp
+++ b/kernel/arch/i386/APIC.cpp
@@ -210,8 +210,8 @@ namespace APIC
 
 	static void ParseMADT(RSDPDescriptor* rsdp)
 	{
-		RSDT* root = (RSDT*)(rsdp->revision == 2 ? ((RSDPDescriptor20*)rsdp)->xsdt_address : rsdp->rsdt_address);
-		MMU::Get().AllocatePage((uint32_t)root);
+		RSDT* const root = (RSDT*)(rsdp->revision == 2 ? ((RSDPDescriptor20*)rsdp)->xsdt_address : rsdp->rsdt_address);
+		MMU::Get().AllocatePage((uintptr_t)root);
 		uint32_t sdt_entry_count = (root->header.length - sizeof(root->header)) / (rsdp->revision == 2 ? 8 : 4);
 
 		for (uint32_t i = 0; i < sdt_entry_count; i++)
@@ -305,6 +305,7 @@ namespace APIC
 				}
 			}
 		}
+		MMU::Get().UnAllocatePage((uintptr_t)root);
 	}
 
 	static uint32_t ReadLocalAPIC(uint32_t offset)
diff --git a/kernel/arch/i386/MMU.cpp b/kernel/arch/i386/MMU.cpp
index e5d15b9ba2..e49f2a2715 100644
--- a/kernel/arch/i386/MMU.cpp
+++ b/kernel/arch/i386/MMU.cpp
@@ -96,3 +96,30 @@ void MMU::AllocateRange(uintptr_t address, ptrdiff_t size)
 	for (uintptr_t page = s_page; page <= e_page; page += PAGE_SIZE)
 		AllocatePage(page);
 }
+
+void MMU::UnAllocatePage(uintptr_t address)
+{
+	uint32_t pdpte = (address & 0xC0000000) >> 30;
+	uint32_t pde   = (address & 0x3FE00000) >> 21;
+	uint32_t pte   = (address & 0x001FF000) >> 12;
+
+	uint64_t* page_directory = (uint64_t*)(m_page_descriptor_pointer_table[pdpte] & PAGE_MASK);
+	ASSERT(page_directory[pde] & PRESENT);
+
+	uint64_t* page_table = (uint64_t*)(page_directory[pde] & PAGE_MASK);
+	ASSERT(page_table[pte] & PRESENT);
+
+	page_table[pte] = 0;
+
+	// TODO: Unallocate the page table if this was the only allocated page
+
+	asm volatile("invlpg (%0)" :: "r"(address & PAGE_MASK) : "memory");
+}
+
+void MMU::UnAllocateRange(uintptr_t address, ptrdiff_t size)
+{
+	uintptr_t s_page = address & PAGE_MASK;
+	uintptr_t e_page = (address + size - 1) & PAGE_MASK;
+	for (uintptr_t page = s_page; page <= e_page; page += PAGE_SIZE)
+		UnAllocatePage(page);
+}
diff --git a/kernel/include/kernel/MMU.h b/kernel/include/kernel/MMU.h
index d47fee5168..9dccc8c5e4 100644
--- a/kernel/include/kernel/MMU.h
+++ b/kernel/include/kernel/MMU.h
@@ -11,7 +11,10 @@ public:
 
 	void AllocatePage(uintptr_t);
 	void AllocateRange(uintptr_t, ptrdiff_t);
-	
+
+	void UnAllocatePage(uintptr_t);
+	void UnAllocateRange(uintptr_t, ptrdiff_t);
+
 private:
 	MMU();