Add a Bitmap class to provide common functionality and use that in the MemoryManager

kernel/src/boot/Init.cpp

@@ -31,5 +31,5 @@ void Init::early_init()
 
     CPU::platform_init();
 
-    MemoryManager::protect_kernel_sections().release_value();
+    MemoryManager::protect_kernel_sections().expect_release_value("We should succeed to protect sections");
 }

kernel/src/memory/MemoryManager.cpp

@@ -1,11 +1,14 @@
 #include "memory/MemoryManager.h"
 #include "Log.h"
+#include "arch/CPU.h"
 #include "arch/MMU.h"
 #include "boot/bootboot.h"
 #include <luna/Alignment.h>
+#include <luna/Bitmap.h>
 #include <luna/String.h>
 #include <luna/SystemError.h>
 #include <luna/Types.h>
+#include <luna/Units.h>
 
 extern BOOTBOOT bootboot;
 
@@ -14,34 +17,37 @@ extern u8 end_of_kernel_rodata[1];
 extern u8 start_of_kernel_data[1];
 extern u8 end_of_kernel_data[1];
 
-static bool page_bitmap_read(u64 index);
-static void page_bitmap_set(u64 index, bool value);
-
 static u64 free_mem = 0;
 static u64 used_mem = 0;
 static u64 reserved_mem = 0;
 
-static char* page_bitmap_addr = nullptr;
-static char* page_virtual_bitmap_addr = nullptr;
-static u64 page_bitmap_size;
-
 static u64 start_index = 0;
 
-static bool page_bitmap_read(u64 index)
-{
-    return (page_virtual_bitmap_addr[index / 8] & (0b10000000 >> (index % 8))) > 0;
-}
-
-static void page_bitmap_set(u64 index, bool value)
-{
-    u64 byte_index = index / 8;
-    u8 mask = 0b10000000 >> (index % 8);
-    page_virtual_bitmap_addr[byte_index] &= (u8)(~mask);
-    if (value) { page_virtual_bitmap_addr[byte_index] |= mask; }
-}
+static Bitmap g_frame_bitmap;
 
 #define CHECK_PAGE_ALIGNED(address) check(is_aligned(address, ARCH_PAGE_SIZE))
 
+static usize get_physical_address_space_size()
+{
+    MMapEnt* ptr = &bootboot.mmap;
+    u64 biggest_ptr = 0;
+    u64 biggest_ptr_size = 0;
+    u64 mmap_entries = (bootboot.size - 128) / 16;
+    for (u64 i = 0; i < mmap_entries; i++)
+    {
+        if (MMapEnt_Ptr(ptr) > biggest_ptr)
+        {
+            biggest_ptr = MMapEnt_Ptr(ptr);
+            biggest_ptr_size = MMapEnt_Size(ptr);
+        }
+
+        ptr++;
+    }
+
+    return biggest_ptr + biggest_ptr_size; // This would be the address at the end of the last entry, thus the whole
+                                           // address space that was passed to us.
+}
+
 namespace MemoryManager
 {
     Result<void> protect_kernel_sections()
@@ -57,12 +63,12 @@ namespace MemoryManager
         return {};
     }
 
-    void init_physical_allocator()
+    void init_physical_frame_allocator()
     {
         u64 total_mem = 0;
 
-        void* biggest_memory_block = nullptr;
-        u64 biggest_memory_block_size = 0;
+        void* biggest_usable_memory_block = nullptr;
+        u64 biggest_usable_memory_block_size = 0;
 
         // walk the memory map
         MMapEnt* ptr = &bootboot.mmap;
@@ -76,53 +82,62 @@ namespace MemoryManager
                 ptr++;
                 continue;
             }
-            if (size > biggest_memory_block_size)
+            if (size > biggest_usable_memory_block_size)
             {
-                biggest_memory_block = (void*)MMapEnt_Ptr(ptr);
-                biggest_memory_block_size = MMapEnt_Size(ptr);
+                biggest_usable_memory_block = (void*)MMapEnt_Ptr(ptr);
+                biggest_usable_memory_block_size = MMapEnt_Size(ptr);
             }
             ptr++;
         }
 
-        page_bitmap_addr = (char*)biggest_memory_block;
-        page_virtual_bitmap_addr = page_bitmap_addr; // we'll map this to virtual memory as soon as the MMU is ready
-        if ((total_mem / ARCH_PAGE_SIZE / 8) >= biggest_memory_block_size)
+        // The entire physical address space. May contain inexistent memory holes, thus differs from total_mem which
+        // only counts existent memory. Our bitmap needs to have space for all of the physical address space, since
+        // usable addresses will be scattered across it.
+        usize physical_address_space_size = get_physical_address_space_size();
+
+        char* frame_bitmap_addr = (char*)biggest_usable_memory_block;
+        usize frame_bitmap_size = physical_address_space_size / ARCH_PAGE_SIZE / 8 + 1;
+
+        // This should never happen, unless memory is very fragmented. Usually there is always a very big block of
+        // usable memory and then some tiny blocks around it.
+        if (frame_bitmap_size >= biggest_usable_memory_block_size) [[unlikely]]
         {
-            kerrorln("ERROR: No single memory block is enough to hold the page bitmap");
-            for (;;)
-                ;
+            kerrorln("ERROR: No single memory block is enough to hold the frame bitmap");
+            CPU::efficient_halt();
         }
 
-        page_bitmap_size = total_mem / ARCH_PAGE_SIZE / 8 + 1;
-        memset(page_bitmap_addr, 0xFF, page_bitmap_size);
+        g_frame_bitmap.initialize(frame_bitmap_addr, frame_bitmap_size);
+
+        g_frame_bitmap.clear(true); // Set all pages to used/reserved by default, then clear out the free ones
 
         ptr = &bootboot.mmap;
         for (u64 i = 0; i < mmap_entries; i++)
         {
             u64 index = MMapEnt_Ptr(ptr) / ARCH_PAGE_SIZE;
+            u64 pages = MMapEnt_Size(ptr) / ARCH_PAGE_SIZE;
             if (!MMapEnt_IsFree(ptr)) { reserved_mem += MMapEnt_Size(ptr); }
             else
             {
                 free_mem += MMapEnt_Size(ptr);
-                for (u64 j = 0; j < (MMapEnt_Size(ptr) / ARCH_PAGE_SIZE); j++) { page_bitmap_set(index + j, false); }
+                g_frame_bitmap.clear_region(index, pages, false);
             }
             ptr++;
         }
 
-        lock_frames((u64)page_bitmap_addr, page_bitmap_size / ARCH_PAGE_SIZE + 1);
+        lock_frames((u64)frame_bitmap_addr, frame_bitmap_size / ARCH_PAGE_SIZE + 1);
     }
 
     void init()
     {
-        init_physical_allocator();
+        init_physical_frame_allocator();
         MMU::setup_initial_page_directory();
     }
 
     void lock_frame(u64 frame)
     {
         const u64 index = ((u64)frame) / ARCH_PAGE_SIZE;
-        if (page_bitmap_read(index)) return;
-        page_bitmap_set(index, true);
+        if (g_frame_bitmap.get(index)) return;
+        g_frame_bitmap.set(index, true);
         used_mem += ARCH_PAGE_SIZE;
         free_mem -= ARCH_PAGE_SIZE;
     }
@@ -134,10 +149,10 @@ namespace MemoryManager
 
     Result<u64> alloc_frame()
     {
-        for (u64 index = start_index; index < (page_bitmap_size * 8); index++)
+        for (u64 index = start_index; index < g_frame_bitmap.size(); index++)
         {
-            if (page_bitmap_read(index)) continue;
-            page_bitmap_set(index, true);
+            if (g_frame_bitmap.get(index)) continue;
+            g_frame_bitmap.set(index, true);
             start_index = index + 1;
             free_mem -= ARCH_PAGE_SIZE;
             used_mem += ARCH_PAGE_SIZE;
@@ -150,9 +165,9 @@ namespace MemoryManager
     Result<void> free_frame(u64 frame)
     {
         const u64 index = frame / ARCH_PAGE_SIZE;
-        if (index > (page_bitmap_size * 8)) return err(EFAULT);
-        if (!page_bitmap_read(index)) return err(EFAULT);
-        page_bitmap_set(index, false);
+        if (index > g_frame_bitmap.size()) return err(EFAULT);
+        if (!g_frame_bitmap.get(index)) return err(EFAULT);
+        g_frame_bitmap.set(index, false);
         used_mem -= ARCH_PAGE_SIZE;
         free_mem += ARCH_PAGE_SIZE;
         if (start_index > index) start_index = index;

luna/CMakeLists.txt

@@ -6,6 +6,7 @@ set(FREESTANDING_SOURCES
     src/String.cpp
     src/Units.cpp
     src/SystemError.cpp
+    src/Bitmap.cpp
 )
 
 set(SOURCES

luna/include/luna/Bitmap.h

@@ -0,0 +1,43 @@
+#pragma once
+#include <luna/Types.h>
+
+class Bitmap
+{
+  public:
+    Bitmap();
+    Bitmap(void* location, usize size_in_bytes);
+
+    void initialize(void* location, usize size_in_bytes);
+    void* move(void* new_location, usize new_location_size_in_bytes);
+
+    void set(usize index, bool value);
+    bool get(usize index);
+
+    // size() returns size in bits! If you want the size in bytes, call size_in_bytes().
+    usize size()
+    {
+        return m_size_in_bytes * 8;
+    }
+
+    usize size_in_bytes()
+    {
+        return m_size_in_bytes;
+    }
+
+    void* location()
+    {
+        return (void*)m_location;
+    }
+
+    bool initialized()
+    {
+        return m_location;
+    }
+
+    void clear(bool value);
+    void clear_region(usize start, usize bits, bool value);
+
+  private:
+    char* m_location = nullptr;
+    usize m_size_in_bytes = 0;
+};

luna/src/Bitmap.cpp

@@ -0,0 +1,88 @@
+#include <luna/Bitmap.h>
+#include <luna/Check.h>
+#include <luna/String.h>
+
+Bitmap::Bitmap()
+{
+}
+
+Bitmap::Bitmap(void* location, usize size_in_bytes) : m_location((char*)location), m_size_in_bytes(size_in_bytes)
+{
+}
+
+void Bitmap::initialize(void* location, usize size_in_bytes)
+{
+    m_location = (char*)location;
+    m_size_in_bytes = size_in_bytes;
+}
+
+void* Bitmap::move(void* new_location, usize new_location_size_in_bytes)
+{
+    expect(initialized(), "Bitmap was never initialized");
+
+    if (new_location_size_in_bytes > m_size_in_bytes) memcpy(new_location, m_location, m_size_in_bytes);
+    else
+        memcpy(new_location, m_location, new_location_size_in_bytes);
+
+    void* old_location = (void*)m_location;
+
+    m_location = (char*)new_location;
+    m_size_in_bytes = new_location_size_in_bytes;
+
+    return old_location;
+}
+
+void Bitmap::set(usize index, bool value)
+{
+    expect(initialized(), "Bitmap was never initialized");
+    expect(index < size(), "Bitmap access out of range");
+    u64 byte_index = index / 8;
+    u8 bit_mask = 0b10000000 >> (index % 8);
+    m_location[byte_index] &= (u8)(~bit_mask);
+    if (value) { m_location[byte_index] |= bit_mask; }
+}
+
+bool Bitmap::get(usize index)
+{
+    expect(initialized(), "Bitmap was never initialized");
+    expect(index < size(), "Bitmap access out of range");
+    usize byte_index = index / 8;
+    usize bit_mask = 0b10000000 >> (index % 8);
+    return (m_location[byte_index] & bit_mask) > 0;
+}
+
+void Bitmap::clear(bool value)
+{
+    expect(initialized(), "Bitmap was never initialized");
+    u8 value_byte = value ? 0xff : 0;
+    memset(m_location, value_byte, m_size_in_bytes);
+}
+
+void Bitmap::clear_region(usize start, usize bits, bool value)
+{
+    expect(initialized(), "Bitmap was never initialized");
+    expect((start + bits) <= size(), "Bitmap clear out of range");
+
+    u8 value_byte = value ? 0xff : 0;
+
+    // Set individual bits while not on a byte boundary.
+    while ((start % 8) && bits--)
+    {
+        set(start, value);
+        start++;
+    }
+
+    // Clear out the rest in bytes.
+    usize bytes = bits / 8;
+
+    memset(&m_location[start / 8], value_byte, bytes);
+    start += bytes * 8;
+    bits -= bytes * 8;
+
+    // Set the remaining individual bits.
+    while (bits--)
+    {
+        set(start, value);
+        start++;
+    }
+}