Kernel: Reorganize memory layout a bit

Move the kernel image to the 1 MB physical mark. This prevents it from
colliding with stuff like the VGA memory. This was causing us to end
up with the BIOS screen contents sneaking into kernel memory sometimes.

This patch also bumps the kmalloc heap size from 1 MB to 3 MB. It's not
the perfect permanent solution (obviously) but it should get the OOM
monkey off our backs for a while.

Kernel/Heap/kmalloc.cpp

@@ -20,15 +20,13 @@ struct [[gnu::packed]] allocation_t
     size_t nchunk;
 };
 
+#define BASE_PHYSICAL (4 * MB)
 #define CHUNK_SIZE 8
-#define POOL_SIZE (1024 * 1024)
+#define POOL_SIZE (3 * MB)
 
-#define ETERNAL_BASE_PHYSICAL (1 * MB)
+#define ETERNAL_BASE_PHYSICAL (2 * MB)
 #define ETERNAL_RANGE_SIZE (2 * MB)
 
-#define BASE_PHYSICAL (3 * MB)
-#define RANGE_SIZE (1 * MB)
-
 static u8 alloc_map[POOL_SIZE / CHUNK_SIZE / 8];
 
 volatile size_t sum_alloc = 0;

Kernel/Makefile

@@ -113,7 +113,7 @@ CXXFLAGS += -nostdlib -nostdinc -nostdinc++
 CXXFLAGS += -I../Toolchain/Local/i686-pc-serenity/include/c++/8.3.0/
 CXXFLAGS += -I../Toolchain/Local/i686-pc-serenity/include/c++/8.3.0/i686-pc-serenity/
 DEFINES += -DKERNEL
-LDFLAGS += -Ttext 0x10000 -Wl,-T linker.ld -nostdlib
+LDFLAGS += -Ttext 0x100000 -Wl,-T linker.ld -nostdlib
 
 all: $(KERNEL) kernel.map
 

Kernel/VM/MemoryManager.cpp

@@ -22,6 +22,7 @@ MemoryManager& MM
 
 MemoryManager::MemoryManager()
 {
+    // FIXME: Hard-coding these is stupid. Find a better way.
     m_kernel_page_directory = PageDirectory::create_at_fixed_address(PhysicalAddress(0x4000));
     m_page_table_zero = (PageTableEntry*)0x6000;
     m_page_table_one = (PageTableEntry*)0x7000;
@@ -61,25 +62,31 @@ void MemoryManager::initialize_paging()
     map_protected(VirtualAddress(0), PAGE_SIZE);
 
 #ifdef MM_DEBUG
-    dbgprintf("MM: Identity map bottom 5MB\n");
+    dbgprintf("MM: Identity map bottom 8MB\n");
 #endif
-    // The bottom 5 MB (except for the null page) are identity mapped & supervisor only.
+    // The bottom 8 MB (except for the null page) are identity mapped & supervisor only.
     // Every process shares these mappings.
-    create_identity_mapping(kernel_page_directory(), VirtualAddress(PAGE_SIZE), (5 * MB) - PAGE_SIZE);
+    create_identity_mapping(kernel_page_directory(), VirtualAddress(PAGE_SIZE), (8 * MB) - PAGE_SIZE);
 
-    // Basic memory map:
+    // FIXME: We should move everything kernel-related above the 0xc0000000 virtual mark.
-    // 0      -> 512 kB         Kernel code. Root page directory & PDE 0.
+
-    // (last page before 1MB)   Used by quickmap_page().
+    // Basic physical memory map:
-    // 1 MB   -> 3 MB           kmalloc_eternal() space.
+    // 0      -> 1 MB           We're just leaving this alone for now.
-    // 3 MB   -> 4 MB           kmalloc() space.
+    // 1      -> 3 MB           Kernel image.
-    // 4 MB   -> 5 MB           Supervisor physical pages (available for allocation!)
+    // (last page before 2MB)   Used by quickmap_page().
-    // 5 MB   -> 0xc0000000     Userspace physical pages (available for allocation!)
+    // 2 MB   -> 4 MB           kmalloc_eternal() space.
-    // 0xc0000000-0xffffffff    Kernel-only virtual address space
+    // 4 MB   -> 7 MB           kmalloc() space.
+    // 7 MB   -> 8 MB           Supervisor physical pages (available for allocation!)
+    // 8 MB   -> MAX            Userspace physical pages (available for allocation!)
+
+    // Basic virtual memory map:
+    // 0 MB   -> 8MB            Identity mapped.
+    // 0xc0000000-0xffffffff    Kernel-only virtual address space.
 
 #ifdef MM_DEBUG
     dbgprintf("MM: Quickmap will use %p\n", m_quickmap_addr.get());
 #endif
-    m_quickmap_addr = VirtualAddress((1 * MB) - PAGE_SIZE);
+    m_quickmap_addr = VirtualAddress((2 * MB) - PAGE_SIZE);
 
     RefPtr<PhysicalRegion> region;
     bool region_is_super = false;
@@ -126,9 +133,9 @@ void MemoryManager::initialize_paging()
         for (size_t page_base = mmap->addr; page_base < (mmap->addr + mmap->len); page_base += PAGE_SIZE) {
             auto addr = PhysicalAddress(page_base);
 
-            if (page_base < 4 * MB) {
+            if (page_base < 7 * MB) {
                 // nothing
-            } else if (page_base >= 4 * MB && page_base < 5 * MB) {
+            } else if (page_base >= 7 * MB && page_base < 8 * MB) {
                 if (region.is_null() || !region_is_super || region->upper().offset(PAGE_SIZE) != addr) {
                     m_super_physical_regions.append(PhysicalRegion::create(addr, addr));
                     region = m_super_physical_regions.last();

Kernel/linker.ld

@@ -2,7 +2,7 @@ ENTRY(start)
 
 SECTIONS
 {
-	. = 0x10000;
+	. = 0x100000;
 
 	.text BLOCK(4K) : ALIGN(4K)
 	{