More paging stuff.

The test userspace process now runs at linear address 0x300000 which is
mapped to a dynamically allocated page from the MemoryManager. Cool!

Kernel/MemoryManager.cpp

@@ -4,6 +4,7 @@
 #include <AK/kmalloc.h>
 #include "i386.h"
 #include "StdLib.h"
+#include "Task.h"
 
 static MemoryManager* s_the;
 
@@ -16,6 +17,7 @@ MemoryManager::MemoryManager()
 {
     m_pageDirectory = (dword*)0x5000;
     m_pageTableZero = (dword*)0x6000;
+    m_pageTableOne = (dword*)0x7000;
 
     initializePaging();
 }
@@ -29,12 +31,19 @@ void MemoryManager::initializePaging()
     static_assert(sizeof(MemoryManager::PageDirectoryEntry) == 4);
     static_assert(sizeof(MemoryManager::PageTableEntry) == 4);
     memset(m_pageTableZero, 0, 4096);
+    memset(m_pageTableOne, 0, 4096);
     memset(m_pageDirectory, 0, 4096);
 
     kprintf("MM: Page directory @ %p\n", m_pageDirectory);
-    kprintf("MM: Page table zero @ %p [0]=%x\n", m_pageTableZero, m_pageTableZero[0]);
-    // Build a basic PDB that identity maps the first 1MB.
+    kprintf("MM: Page table zero @ %p\n", m_pageTableZero);
+    kprintf("MM: Page table one @ %p\n", m_pageTableOne);
+
     identityMap(LinearAddress(0), 4 * MB);
+ 
+    // Put pages between 4MB and 16MB in the page freelist.
+    for (size_t i = (4 * MB) + 1024; i < (16 * MB); i += PAGE_SIZE) {
+        m_freePages.append(PhysicalAddress(i));
+    }
 
     asm volatile("movl %%eax, %%cr3"::"a"(m_pageDirectory));
     asm volatile(
@@ -57,6 +66,11 @@ auto MemoryManager::ensurePTE(LinearAddress linearAddress) -> PageTableEntry
             pde.setUserAllowed(true);
             pde.setPresent(true);
             pde.setWritable(true);
+        } else if (pageDirectoryIndex == 1) {
+            pde.setPageTableBase((dword)m_pageTableOne);
+            pde.setUserAllowed(false);
+            pde.setPresent(true);
+            pde.setWritable(false);
         } else {
             // FIXME: We need an allocator!
             ASSERT_NOT_REACHED();
@@ -75,10 +89,6 @@ void MemoryManager::identityMap(LinearAddress linearAddress, size_t length)
         pte.setUserAllowed(true);
         pte.setPresent(true);
         pte.setWritable(true);
-        if (pteAddress.get() == 0x6023) {
-            kprintf("kek\n");
-            HANG;
-        }
     }
 }
 
@@ -87,4 +97,86 @@ void MemoryManager::initialize()
     s_the = new MemoryManager;
 }
 
+PageFaultResponse MemoryManager::handlePageFault(const PageFault& fault)
+{
+    kprintf("MM: handlePageFault(%w) at laddr=%p\n", fault.code(), fault.address().get());
+    if (fault.isNotPresent()) { 
+        kprintf("  >> NP fault!\n");
+    } else if (fault.isProtectionViolation()) {
+        kprintf("  >> PV fault!\n");
+    }
+    return PageFaultResponse::ShouldCrash;
+}
+
+RetainPtr<Zone> MemoryManager::createZone(size_t size)
+{
+    auto pages = allocatePhysicalPages(ceilDiv(size, PAGE_SIZE));
+    if (pages.isEmpty()) {
+        kprintf("MM: createZone: no physical pages for size %u", size);
+        return nullptr;
+    }
+    return adopt(*new Zone(move(pages)));
+}
+
+Vector<PhysicalAddress> MemoryManager::allocatePhysicalPages(size_t count)
+{
+    kprintf("MM: alloc %u pages from %u available\n", count, m_freePages.size());
+    if (count > m_freePages.size())
+        return { };
+
+    Vector<PhysicalAddress> pages;
+    pages.ensureCapacity(count);
+    for (size_t i = 0; i < count; ++i)
+        pages.append(m_freePages.takeLast());
+    kprintf("MM: returning the pages (%u of them)\n", pages.size());
+    return pages;
+}
+
+byte* MemoryManager::quickMapOnePage(PhysicalAddress physicalAddress)
+{
+    auto pte = ensurePTE(LinearAddress(4 * MB));
+    kprintf("quickmap %x @ %x {pte @ %p}\n", physicalAddress.get(), 4*MB, pte.ptr());
+    pte.setPhysicalPageBase(physicalAddress.pageBase());
+    pte.setPresent(true);
+    pte.setWritable(true);
+    return (byte*)(4 * MB);
+}
+
+bool MemoryManager::unmapZonesForTask(Task& task)
+{
+    return true;
+}
+
+bool MemoryManager::mapZonesForTask(Task& task)
+{
+    for (auto& mappedZone : task.m_mappedZones) {
+        auto& zone = *mappedZone.zone;
+        for (size_t i = 0; i < zone.m_pages.size(); ++i) {
+            auto pte = ensurePTE(mappedZone.linearAddress.offset(i * PAGE_SIZE));
+            pte.setPhysicalPageBase(zone.m_pages[i].get());
+            pte.setPresent(true);
+        }
+    }
+    return true;
+}
+
+bool copyToZone(Zone& zone, const void* data, size_t size)
+{
+    if (zone.size() < size) {
+        kprintf("copyToZone: can't fit %u bytes into zone with size %u\n", size, zone.size());
+        return false;
+    }
+
+    auto* dataptr = (const byte*)data;
+    size_t remaining = size;
+    for (size_t i = 0; i < zone.m_pages.size(); ++i) {
+        byte* dest = MemoryManager::the().quickMapOnePage(zone.m_pages[i]);
+        kprintf("memcpy(%p, %p, %u)\n", dest, dataptr, min(PAGE_SIZE, remaining));
+        memcpy(dest, dataptr, min(PAGE_SIZE, remaining));
+        dataptr += PAGE_SIZE;
+        remaining -= PAGE_SIZE;
+    }
+
+    return true;
+}
 

Kernel/MemoryManager.h

@@ -1,36 +1,39 @@
 #pragma once
 
-#include <AK/Types.h>
+#include "types.h"
+#include "i386.h"
+#include <AK/Retainable.h>
+#include <AK/RetainPtr.h>
+#include <AK/Vector.h>
+#include <AK/HashMap.h>
 
-class PhysicalAddress {
-public:
-    PhysicalAddress() { }
-    explicit PhysicalAddress(dword address) : m_address(address) { }
+class Task;
 
-    dword get() const { return m_address; }
-    void set(dword address) { m_address = address; }
-    void mask(dword m) { m_address &= m; }
-
-private:
-    dword m_address { 0 };
+enum class PageFaultResponse {
+    ShouldCrash,
+    Continue,
 };
 
-class LinearAddress {
+struct Zone : public Retainable<Zone> {
 public:
-    LinearAddress() { }
-    explicit LinearAddress(dword address) : m_address(address) { }
+    ~Zone() { }
+    size_t size() const { return m_pages.size() * PAGE_SIZE; }
 
-    LinearAddress offset(dword o) const { return LinearAddress(m_address + o); }
-    dword get() const { return m_address; }
-    void set(dword address) { m_address = address; }
-    void mask(dword m) { m_address &= m; }
-
-    bool operator==(const LinearAddress& other) const { return m_address == other.m_address; }
+    const Vector<PhysicalAddress>& pages() const { return m_pages; }
 
 private:
-    dword m_address { 0 };
+    friend class MemoryManager;
+    friend bool copyToZone(Zone&, const void* data, size_t);
+    explicit Zone(Vector<PhysicalAddress>&& pages)
+        : m_pages(move(pages))
+    {
+    }
+
+    Vector<PhysicalAddress> m_pages;
 };
 
+bool copyToZone(Zone&, const void* data, size_t);
+
 class MemoryManager {
 public:
     static MemoryManager& the();
@@ -38,6 +41,17 @@ public:
     PhysicalAddress pageDirectoryBase() const { return PhysicalAddress(reinterpret_cast<dword>(m_pageDirectory)); }
 
     static void initialize();
+
+    PageFaultResponse handlePageFault(const PageFault&);
+
+    RetainPtr<Zone> createZone(size_t);
+
+    // HACK: don't use this jeez :(
+    byte* quickMapOnePage(PhysicalAddress);
+
+    bool mapZonesForTask(Task&);
+    bool unmapZonesForTask(Task&);
+
 private:
     MemoryManager();
     ~MemoryManager();
@@ -46,6 +60,8 @@ private:
 
     void identityMap(LinearAddress, size_t length);
 
+    Vector<PhysicalAddress> allocatePhysicalPages(size_t count);
+
     struct PageDirectoryEntry {
         explicit PageDirectoryEntry(dword* pde) : m_pde(pde) { }
 
@@ -128,4 +144,9 @@ private:
 
     dword* m_pageDirectory;
     dword* m_pageTableZero;
+    dword* m_pageTableOne;
+
+    HashMap<int, RetainPtr<Zone>> m_zones;
+
+    Vector<PhysicalAddress> m_freePages;
 };

Kernel/Syscall.cpp

@@ -45,34 +45,6 @@ void initialize()
     kprintf("syscall: int 0x80 handler installed\n");
 }
 
-DWORD invoke(DWORD function)
-{
-    DWORD result;
-    asm("int $0x80":"=a"(result):"a"(function));
-    return result;
-}
-
-DWORD invoke(DWORD function, DWORD arg1)
-{
-    DWORD result;
-    asm("int $0x80":"=a"(result):"a"(function),"d"(arg1));
-    return result;
-}
-
-DWORD invoke(DWORD function, DWORD arg1, DWORD arg2)
-{
-    DWORD result;
-    asm("int $0x80":"=a"(result):"a"(function),"d"(arg1),"c"(arg2));
-    return result;
-}
-
-DWORD invoke(DWORD function, DWORD arg1, DWORD arg2, DWORD arg3)
-{
-    DWORD result;
-    asm volatile("int $0x80":"=a"(result):"a"(function),"d"(arg1),"c"(arg2),"b"(arg3));
-    return result;
-}
-
 DWORD handle(DWORD function, DWORD arg1, DWORD arg2, DWORD arg3)
 {
     switch (function) {

Kernel/Syscall.h

@@ -19,9 +19,33 @@ enum Function {
 };
 
 void initialize();
-DWORD invoke(DWORD function);
-DWORD invoke(DWORD function, DWORD arg1);
-DWORD invoke(DWORD function, DWORD arg1, DWORD arg2);
-DWORD invoke(DWORD function, DWORD arg1, DWORD arg2, DWORD arg3);
+
+inline DWORD invoke(DWORD function)
+{
+    DWORD result;
+    asm("int $0x80":"=a"(result):"a"(function));
+    return result;
+}
+
+inline DWORD invoke(DWORD function, DWORD arg1)
+{
+    DWORD result;
+    asm("int $0x80":"=a"(result):"a"(function),"d"(arg1));
+    return result;
+}
+
+inline DWORD invoke(DWORD function, DWORD arg1, DWORD arg2)
+{
+    DWORD result;
+    asm("int $0x80":"=a"(result):"a"(function),"d"(arg1),"c"(arg2));
+    return result;
+}
+
+inline DWORD invoke(DWORD function, DWORD arg1, DWORD arg2, DWORD arg3)
+{
+    DWORD result;
+    asm volatile("int $0x80":"=a"(result):"a"(function),"d"(arg1),"c"(arg2),"b"(arg3));
+    return result;
+}
 
 }

Kernel/Task.cpp

@@ -92,6 +92,14 @@ void Task::allocateLDT()
     m_tss.ldt = newLDTSelector;
 }
 
+bool Task::mapZone(LinearAddress address, RetainPtr<Zone>&& zone)
+{
+    // FIXME: This needs sanity checks. What if this overlaps existing zones?
+    kprintf("mapped zone with size %u at %x\n", zone->size(), address.get());
+    m_mappedZones.append({ address, move(zone) });
+    return true;
+}
+
 Task::Task(void (*e)(), const char* n, IPC::Handle h, RingLevel ring)
     : m_name(n)
     , m_entry(e)
@@ -100,6 +108,19 @@ Task::Task(void (*e)(), const char* n, IPC::Handle h, RingLevel ring)
     , m_state(Runnable)
     , m_ring(ring)
 {
+    if (!isRing0()) {
+        auto zone = MemoryManager::the().createZone(PAGE_SIZE);
+        ASSERT(zone);
+
+        kprintf("New task zone: { size: %u }\n", zone->size());
+
+        bool success = mapZone(LinearAddress(0x300000), zone.copyRef());
+        ASSERT(success);
+
+        success = copyToZone(*zone, (void*)e, PAGE_SIZE);
+        ASSERT(success);
+    }
+
     memset(&m_tss, 0, sizeof(m_tss));
     memset(&m_ldtEntries, 0, sizeof(m_ldtEntries));
 
@@ -133,7 +154,13 @@ Task::Task(void (*e)(), const char* n, IPC::Handle h, RingLevel ring)
 
     m_tss.cr3 = MemoryManager::the().pageDirectoryBase().get();
 
-    m_tss.eip = (DWORD)m_entry;
+    if (isRing0()) {
+        m_tss.eip = (DWORD)m_entry;
+    } else {
+        m_tss.eip = m_mappedZones[0].linearAddress.get();
+    }
+
+    kprintf("basically ready\n");
 
     // NOTE: Each task gets 4KB of stack.
     // This memory is leaked ATM.
@@ -165,7 +192,7 @@ Task::Task(void (*e)(), const char* n, IPC::Handle h, RingLevel ring)
 
     system.nprocess++;
 
-    kprintf("Task %u (%s) spawned @ %p\n", m_pid, m_name.characters(), m_entry);
+    kprintf("Task %u (%s) spawned @ %p\n", m_pid, m_name.characters(), m_tss.eip);
 }
 
 Task::~Task()
@@ -300,6 +327,11 @@ static bool contextSwitch(Task* t)
     if (current->state() == Task::Running)
         current->setState(Task::Runnable);
 
+    bool success = MemoryManager::the().unmapZonesForTask(*current);
+    ASSERT(success);
+    success = MemoryManager::the().mapZonesForTask(*t);
+    ASSERT(success);
+
     current = t;
     t->setState(Task::Running);
 

Kernel/Task.h

@@ -11,6 +11,7 @@
 //#define TASK_SANITY_CHECKS
 
 class FileHandle;
+class Zone;
 
 class Task : public InlineLinkedListNode<Task> {
     friend class InlineLinkedListNode<Task>;
@@ -97,6 +98,9 @@ public:
     static void taskDidCrash(Task*);
 
 private:
+    friend class MemoryManager;
+
+    bool mapZone(LinearAddress, RetainPtr<Zone>&&);
     FileHandle* openFile(String&&);
 
     void allocateLDT();
@@ -120,6 +124,13 @@ private:
     Vector<OwnPtr<FileHandle>> m_fileHandles;
     RingLevel m_ring { Ring0 };
     int m_error { 0 };
+
+    struct MappedZone {
+        LinearAddress linearAddress;
+        RetainPtr<Zone> zone;
+    };
+
+    Vector<MappedZone> m_mappedZones;
 };
 
 extern void task_init();

Kernel/i386.cpp

@@ -4,6 +4,7 @@
 #include "i386.h"
 #include "Assertions.h"
 #include "Task.h"
+#include "MemoryManager.h"
 
 struct DescriptorTablePointer {
     WORD size;
@@ -67,8 +68,8 @@ asm( \
     "    iret\n" \
 );
 
-EH_ENTRY(13)
-
+// 13: General Protection Fault
+EH_ENTRY(13);
 void exception_13_handler()
 {
     auto& regs = *reinterpret_cast<RegisterDump*>(exception_state_dump);
@@ -88,6 +89,42 @@ void exception_13_handler()
     Task::taskDidCrash(current);
 }
 
+// 14: Page Fault
+EH_ENTRY(14);
+void exception_14_handler()
+{
+    dword faultAddress;
+    asm ("movl %%cr2, %%eax":"=a"(faultAddress));
+
+    auto& regs = *reinterpret_cast<RegisterDump*>(exception_state_dump);
+    kprintf("%s page fault: %u(%s), %s laddr=%p\n",
+        current->isRing0() ? "Kernel" : "User",
+        current->pid(),
+        current->name().characters(),
+        exception_code & 2 ? "write" : "read",
+        faultAddress);
+
+    kprintf("exception code: %w\n", exception_code);
+    kprintf("pc=%w:%x ds=%w es=%w fs=%w gs=%w\n", regs.cs, regs.eip, regs.ds, regs.es, regs.fs, regs.gs);
+    kprintf("eax=%x ebx=%x ecx=%x edx=%x\n", regs.eax, regs.ebx, regs.ecx, regs.edx);
+    kprintf("ebp=%x esp=%x esi=%x edi=%x\n", regs.ebp, regs.esp, regs.esi, regs.edi);
+
+    if (current->isRing0())
+        HANG;
+
+    auto response = MemoryManager::the().handlePageFault(PageFault(exception_code, LinearAddress(faultAddress)));
+
+    if (response == PageFaultResponse::ShouldCrash) {
+        kprintf("Crashing after unresolved page fault\n");
+        // NOTE: This will schedule a new task.
+        Task::taskDidCrash(current);
+    } else if (response == PageFaultResponse::Continue) {
+        kprintf("Continuing after resolved page fault\n");
+    } else {
+        ASSERT_NOT_REACHED();
+    }
+}
+
 #define EH(i, msg) \
     static void _exception ## i () \
     { \
@@ -227,7 +264,7 @@ void idt_init()
     registerInterruptHandler(0x0b, _exception11);
     registerInterruptHandler(0x0c, _exception12);
     registerInterruptHandler(0x0d, exception_13_entry);
-    registerInterruptHandler(0x0e, _exception14);
+    registerInterruptHandler(0x0e, exception_14_entry);
     registerInterruptHandler(0x0f, _exception15);
     registerInterruptHandler(0x10, _exception16);
 

Kernel/i386.h

@@ -2,6 +2,8 @@
 
 #include "types.h"
 
+#define PAGE_SIZE 4096u
+
 union Descriptor {
     struct {
         WORD limit_lo;
@@ -76,6 +78,42 @@ void writeGDTEntry(WORD selector, Descriptor&);
 /* Map IRQ0-15 @ ISR 0x50-0x5F */
 #define IRQ_VECTOR_BASE 0x50
 
+struct PageFaultFlags {
+enum Flags {
+    NotPresent = 0x00,
+    ProtectionViolation = 0x01,
+    Read = 0x00,
+    Write = 0x02,
+    UserMode = 0x04,
+    SupervisorMode = 0x00,
+    InstructionFetch = 0x08,
+};
+};
+
+class PageFault {
+public:
+    PageFault(word code, LinearAddress address)
+        : m_code(code)
+        , m_address(address)
+    {
+    }
+
+    LinearAddress address() const { return m_address; }
+    word code() const { return m_code; }
+
+    bool isNotPresent() const { return (m_code & 1) == PageFaultFlags::NotPresent; }
+    bool isProtectionViolation() const { return (m_code & 1) == PageFaultFlags::ProtectionViolation; }
+    bool isRead() const { return (m_code & 2) == PageFaultFlags::Read; }
+    bool isWrite() const { return (m_code & 2) == PageFaultFlags::Write; }
+    bool isUser() const { return (m_code & 4) == PageFaultFlags::UserMode; }
+    bool isSupervisor() const { return (m_code & 4) == PageFaultFlags::SupervisorMode; }
+    bool isInstructionFetch() const { return (m_code & 8) == PageFaultFlags::InstructionFetch; }
+
+private:
+    word m_code;
+    LinearAddress m_address;
+};
+
 struct RegisterDump {
     WORD gs;
     WORD fs;
@@ -95,3 +133,8 @@ struct RegisterDump {
     DWORD eflags;
 } PACKED;
 
+inline constexpr dword pageBaseOf(dword address)
+{
+    return address & 0xfffff000;
+}
+

Kernel/init.cpp

@@ -68,7 +68,7 @@ static void user_main()
     DO_SYSCALL_A3(0x3000, 2, 3, 4);
     // Crash ourselves!
     char* x = reinterpret_cast<char*>(0xbeefbabe);
-    //*x = 1;
+    *x = 1;
     HANG;
     for (;;) {
         // nothing?
@@ -158,7 +158,7 @@ void init()
 
     //vfs->listDirectory("/");
 
-#if 1
+#if 0
     {
         auto motdFile = vfs->open("/motd.txt");
         ASSERT(motdFile);

Kernel/types.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <AK/Types.h>
+
 #define PACKED __attribute__ ((packed))
 #define NORETURN __attribute__ ((noreturn))
 #define PURE __attribute__ ((pure))
@@ -26,3 +28,42 @@ struct FarPtr {
     DWORD offset { 0 };
     WORD selector { 0 };
 } PACKED;
+
+class PhysicalAddress {
+public:
+    PhysicalAddress() { }
+    explicit PhysicalAddress(dword address) : m_address(address) { }
+
+    dword get() const { return m_address; }
+    void set(dword address) { m_address = address; }
+    void mask(dword m) { m_address &= m; }
+
+    byte* asPtr() { return reinterpret_cast<byte*>(m_address); }
+    const byte* asPtr() const { return reinterpret_cast<const byte*>(m_address); }
+
+    dword pageBase() const { return m_address & 0xfffff000; }
+
+private:
+    dword m_address { 0 };
+};
+
+class LinearAddress {
+public:
+    LinearAddress() { }
+    explicit LinearAddress(dword address) : m_address(address) { }
+
+    LinearAddress offset(dword o) const { return LinearAddress(m_address + o); }
+    dword get() const { return m_address; }
+    void set(dword address) { m_address = address; }
+    void mask(dword m) { m_address &= m; }
+
+    bool operator==(const LinearAddress& other) const { return m_address == other.m_address; }
+
+    byte* asPtr() { return reinterpret_cast<byte*>(m_address); }
+    const byte* asPtr() const { return reinterpret_cast<const byte*>(m_address); }
+
+    dword pageBase() const { return m_address & 0xfffff000; }
+
+private:
+    dword m_address { 0 };
+};