x86_64: Add a friendlier handler for page faults

Much better now!!

README.md

@@ -1,5 +1,5 @@
 # Luna
-A simple kernel and userspace for the x86_64 platform, written mostly in C++ and C. (rewrite, listed features are currently mostly from the old version) [![Build Status](https://drone.cloudapio.eu/api/badges/apio/Luna/status.svg?ref=refs/heads/restart)](https://drone.cloudapio.eu/apio/Luna)
+A simple kernel and userspace for the x86_64 platform, written mostly in C++ and C. [![Build Status](https://drone.cloudapio.eu/api/badges/apio/Luna/status.svg?ref=refs/heads/restart)](https://drone.cloudapio.eu/apio/Luna) (rewrite, listed features are currently mostly from the old version)
 
 ## Features
 - x86_64-compatible [kernel](kernel/).

kernel/CMakeLists.txt

@@ -7,6 +7,7 @@ set(SOURCES
     src/video/TextConsole.cpp
     src/memory/MemoryManager.cpp
     src/memory/Heap.cpp
+    src/memory/KernelVM.cpp
     src/memory/MemoryMap.cpp
     src/boot/Init.cpp
     src/arch/Serial.cpp

kernel/src/arch/x86_64/CPU.cpp

@@ -293,7 +293,15 @@ static void setup_idt()
     kerrorln("FIXME(interrupt): %s", name);                                                                            \
     CPU::efficient_halt();
 
-extern "C" void handle_x86_exception([[maybe_unused]] Registers* regs)
+[[noreturn]] void handle_page_fault(Registers* regs)
+{
+    u64 cr2;
+    asm volatile("mov %%cr2, %0" : "=r"(cr2));
+    kerrorln("Page fault at RIP %lx while accessing %lx!", regs->rip, cr2);
+    CPU::efficient_halt();
+}
+
+extern "C" void handle_x86_exception(Registers* regs)
 {
     switch (regs->isr)
     {
@@ -309,7 +317,7 @@ extern "C" void handle_x86_exception([[maybe_unused]] Registers* regs)
     case 11: FIXME_UNHANDLED_INTERRUPT("Segment not present");
     case 12: FIXME_UNHANDLED_INTERRUPT("Stack-segment fault");
     case 13: FIXME_UNHANDLED_INTERRUPT("General protection fault");
-    case 14: FIXME_UNHANDLED_INTERRUPT("Page fault");
+    case 14: handle_page_fault(regs);
     case 16: FIXME_UNHANDLED_INTERRUPT("x87 floating-point exception");
     case 17: FIXME_UNHANDLED_INTERRUPT("Alignment check");
     case 19: FIXME_UNHANDLED_INTERRUPT("SIMD floating-point exception");

kernel/src/memory/Heap.cpp

@@ -2,6 +2,7 @@
 #include "Log.h"
 #include "arch/MMU.h"
 #include "arch/Serial.h"
+#include "memory/KernelVM.h"
 #include "memory/MemoryManager.h"
 #include <luna/Alignment.h>
 #include <luna/String.h>
@@ -31,20 +32,19 @@ static_assert(sizeof(HeapBlock) == 48UL);
 static HeapBlock* heap_start = nullptr;
 static HeapBlock* heap_end = nullptr;
 
-static usize start_addr = 0xffffffff80000000;
-
 static Result<HeapBlock*> allocate_pages(
     usize count) // FIXME: Keep track of virtual address space usage. For now, since the address
                  // space is so huge, we can just start at a fairly large address and assume
                  // we'll never run into anything, but this will probably bite us in the future.
 {
-    void* const ptr = (void*)TRY(MemoryManager::alloc_at(start_addr, count, MMU::ReadWrite | MMU::NoExecute));
+    u64 virt = TRY(KernelVM::alloc_several_pages(count));
-    if (ptr) start_addr += (count * ARCH_PAGE_SIZE);
+    void* const ptr = (void*)TRY(MemoryManager::alloc_at(virt, count, MMU::ReadWrite | MMU::NoExecute));
     return (HeapBlock*)ptr;
 }
 
 static Result<void> release_pages(void* ptr, usize count)
 {
+    TRY(KernelVM::free_several_pages((u64)ptr, count));
     return MemoryManager::unmap_owned((u64)ptr, count);
 }
 
@@ -176,7 +176,7 @@ Result<void*> kmalloc(usize size)
 
     if (!heap_start)
     {
-        const usize pages = get_pages_for_allocation(size);
+        const usize pages = get_pages_for_allocation(size + sizeof(HeapBlock));
         HeapBlock* const block = TRY(allocate_pages(pages));
 
         block->full_size = (pages * ARCH_PAGE_SIZE) - sizeof(HeapBlock);
@@ -214,7 +214,7 @@ Result<void*> kmalloc(usize size)
 
     if (!block) // No free blocks, let's allocate a new one
     {
-        usize pages = get_pages_for_allocation(size);
+        usize pages = get_pages_for_allocation(size + sizeof(HeapBlock));
         block = TRY(allocate_pages(pages));
 
         block->full_size = (pages * ARCH_PAGE_SIZE) - sizeof(HeapBlock);
@@ -222,6 +222,7 @@ Result<void*> kmalloc(usize size)
         block->status = BLOCK_START_MEM | BLOCK_END_MEM;
         block->next = nullptr;
         block->last = heap_end;
+        heap_end->next = block;
 
         heap_end = block;
     }

kernel/src/memory/KernelVM.cpp

@@ -0,0 +1,104 @@
+#include "memory/KernelVM.h"
+#include "arch/MMU.h"
+#include <luna/Bitmap.h>
+
+static const u64 KERNEL_VM_RANGE_START = 0xfffffffff0000000;
+
+static Bitmap g_kernelvm_bitmap;
+
+static u8 bitmap_memory[4096];
+
+static const usize KERNEL_VM_RANGE_SIZE = (sizeof(bitmap_memory) * 8) * ARCH_PAGE_SIZE;
+
+static const u64 KERNEL_VM_RANGE_END = KERNEL_VM_RANGE_SIZE + KERNEL_VM_RANGE_START;
+
+static_assert(KERNEL_VM_RANGE_END == 0xfffffffff8000000);
+
+static usize g_used_vm;
+
+namespace KernelVM
+{
+    void init()
+    {
+        g_kernelvm_bitmap.initialize(bitmap_memory, sizeof(bitmap_memory));
+    }
+
+    Result<u64> alloc_one_page()
+    {
+        for (u64 index = 0; index < g_kernelvm_bitmap.size(); index++)
+        {
+            if (g_kernelvm_bitmap.get(index)) continue;
+            g_kernelvm_bitmap.set(index, true);
+            g_used_vm += ARCH_PAGE_SIZE;
+            return KERNEL_VM_RANGE_START + (index * ARCH_PAGE_SIZE);
+        }
+
+        return err(ENOMEM);
+    }
+
+    Result<u64> alloc_several_pages(usize count)
+    {
+        u64 first_free_index = 0;
+        u64 free_contiguous_pages = 0;
+        for (u64 index = 0; index < g_kernelvm_bitmap.size(); index++)
+        {
+            if (g_kernelvm_bitmap.get(index))
+            {
+                free_contiguous_pages = 0;
+                continue;
+            }
+
+            // At this point, we have a free page.
+
+            if (!free_contiguous_pages) first_free_index = index;
+            free_contiguous_pages++;
+
+            // Found enough contiguous free pages!!
+            if (free_contiguous_pages == count)
+            {
+                g_used_vm += ARCH_PAGE_SIZE * count;
+                g_kernelvm_bitmap.clear_region(first_free_index, count, true);
+                return KERNEL_VM_RANGE_START + (first_free_index * ARCH_PAGE_SIZE);
+            }
+        }
+
+        return err(ENOMEM);
+    }
+
+    Result<void> free_one_page(u64 address)
+    {
+        if (address < KERNEL_VM_RANGE_START) return err(EFAULT);
+
+        u64 index = (address - KERNEL_VM_RANGE_START) / ARCH_PAGE_SIZE;
+
+        if (index >= g_kernelvm_bitmap.size()) return err(EFAULT);
+
+        g_kernelvm_bitmap.set(index, false);
+        g_used_vm -= ARCH_PAGE_SIZE;
+
+        return {};
+    }
+
+    Result<void> free_several_pages(u64 address, usize count)
+    {
+        if (address < KERNEL_VM_RANGE_START) return err(EFAULT);
+        if (address + (count * ARCH_PAGE_SIZE) >= KERNEL_VM_RANGE_END) return err(EFAULT);
+
+        u64 index = (address - KERNEL_VM_RANGE_START) / ARCH_PAGE_SIZE;
+
+        g_kernelvm_bitmap.clear_region(index, count, false);
+        g_used_vm -= ARCH_PAGE_SIZE * count;
+
+        return {};
+    }
+
+    usize used()
+    {
+        return g_used_vm;
+    }
+
+    usize free()
+    {
+        return KERNEL_VM_RANGE_SIZE - g_used_vm;
+    }
+}

kernel/src/memory/KernelVM.h

@@ -0,0 +1,18 @@
+#pragma once
+#include <luna/Result.h>
+#include <luna/Types.h>
+
+// Simple bitmap allocator which hands out kernel-space virtual addresses for use in kmalloc() and friends.
+namespace KernelVM
+{
+    void init();
+
+    Result<u64> alloc_one_page();
+    Result<u64> alloc_several_pages(usize count);
+
+    Result<void> free_one_page(u64 address);
+    Result<void> free_several_pages(u64 address, usize count);
+
+    usize free();
+    usize used();
+}

kernel/src/memory/MemoryManager.cpp

@@ -2,6 +2,7 @@
 #include "Log.h"
 #include "arch/CPU.h"
 #include "arch/MMU.h"
+#include "memory/KernelVM.h"
 #include "memory/MemoryMap.h"
 #include <luna/Alignment.h>
 #include <luna/Bitmap.h>
@@ -96,6 +97,7 @@ namespace MemoryManager
     void init()
     {
         init_physical_frame_allocator();
+        KernelVM::init();
         MMU::setup_initial_page_directory();
     }