More work on per-process page directories. It basically works now!

I spent some time stuck on a problem where processes would clobber each
other's stacks. Took me a moment to figure out that their stacks
were allocated in the sub-4MB linear address range which is shared
between all processes. Oops!

Kernel/MemoryManager.cpp

@@ -6,6 +6,8 @@
 #include "StdLib.h"
 #include "Task.h"
 
+//#define MM_DEBUG
+
 static MemoryManager* s_the;
 
 MemoryManager& MM
@@ -15,10 +17,12 @@ MemoryManager& MM
 
 MemoryManager::MemoryManager()
 {
-    m_pageDirectory = (dword*)0x5000;
+    m_kernel_page_directory = (dword*)0x5000;
     m_pageTableZero = (dword*)0x6000;
     m_pageTableOne = (dword*)0x7000;
 
+    m_next_laddr.set(0xd0000000);
+
     initializePaging();
 }
 
@@ -26,12 +30,12 @@ MemoryManager::~MemoryManager()
 {
 }
 
-void MemoryManager::populatePageDirectory(Task& task)
+void MemoryManager::populate_page_directory(Task& task)
 {
     memset(task.m_pageDirectory, 0, 4096);
 
-    task.m_pageDirectory[0] = m_pageDirectory[0];
-    task.m_pageDirectory[1] = m_pageDirectory[1];
+    task.m_pageDirectory[0] = m_kernel_page_directory[0];
+    task.m_pageDirectory[1] = m_kernel_page_directory[1];
 }
 
 void MemoryManager::initializePaging()
@@ -40,10 +44,10 @@ void MemoryManager::initializePaging()
     static_assert(sizeof(MemoryManager::PageTableEntry) == 4);
     memset(m_pageTableZero, 0, 4096);
     memset(m_pageTableOne, 0, 4096);
-    memset(m_pageDirectory, 0, 4096);
+    memset(m_kernel_page_directory, 0, 4096);
 
 #ifdef MM_DEBUG
-    kprintf("MM: Page directory @ %p\n", m_pageDirectory);
+    kprintf("MM: Kernel page directory @ %p\n", m_kernel_page_directory);
 #endif
 
     // Make null dereferences crash.
@@ -56,7 +60,7 @@ void MemoryManager::initializePaging()
         m_freePages.append(PhysicalAddress(i));
     }
 
-    asm volatile("movl %%eax, %%cr3"::"a"(m_pageDirectory));
+    asm volatile("movl %%eax, %%cr3"::"a"(m_kernel_page_directory));
     asm volatile(
         "movl %cr0, %eax\n"
         "orl $0x80000001, %eax\n"
@@ -69,19 +73,20 @@ void* MemoryManager::allocatePageTable()
     auto ppages = allocatePhysicalPages(1);
     dword address = ppages[0].get();
     identityMap(LinearAddress(address), 4096);
+    memset((void*)address, 0, 4096);
     return (void*)address;
 }
 
-auto MemoryManager::ensurePTE(dword* pageDirectory, LinearAddress linearAddress) -> PageTableEntry
+auto MemoryManager::ensurePTE(dword* page_directory, LinearAddress laddr) -> PageTableEntry
 {
     ASSERT_INTERRUPTS_DISABLED();
-    dword pageDirectoryIndex = (linearAddress.get() >> 22) & 0x3ff;
-    dword pageTableIndex = (linearAddress.get() >> 12) & 0x3ff;
+    dword pageDirectoryIndex = (laddr.get() >> 22) & 0x3ff;
+    dword pageTableIndex = (laddr.get() >> 12) & 0x3ff;
 
-    PageDirectoryEntry pde = PageDirectoryEntry(&pageDirectory[pageDirectoryIndex]);
+    PageDirectoryEntry pde = PageDirectoryEntry(&page_directory[pageDirectoryIndex]);
     if (!pde.isPresent()) {
 #ifdef MM_DEBUG
-        kprintf("MM: PDE %u not present, allocating\n", pageDirectoryIndex);
+        dbgprintf("MM: PDE %u not present, allocating\n", pageDirectoryIndex);
 #endif
         if (pageDirectoryIndex == 0) {
             pde.setPageTableBase((dword)m_pageTableZero);
@@ -95,8 +100,9 @@ auto MemoryManager::ensurePTE(dword* pageDirectory, LinearAddress linearAddress)
             pde.setWritable(true);
         } else {
             auto* pageTable = allocatePageTable();
-            kprintf("MM: Allocated page table #%u (for laddr=%p) at %p\n", pageDirectoryIndex, linearAddress.get(), pageTable);
-            memset(pageTable, 0, 4096);
+#ifdef MM_DEBUG
+            dbgprintf("MM: PDE %x allocated page table #%u (for laddr=%p) at %p\n", page_directory, pageDirectoryIndex, laddr.get(), pageTable);
+#endif
             pde.setPageTableBase((dword)pageTable);
             pde.setUserAllowed(true);
             pde.setPresent(true);
@@ -112,7 +118,7 @@ void MemoryManager::protectMap(LinearAddress linearAddress, size_t length)
     // FIXME: ASSERT(linearAddress is 4KB aligned);
     for (dword offset = 0; offset < length; offset += 4096) {
         auto pteAddress = linearAddress.offset(offset);
-        auto pte = ensurePTE(m_pageDirectory, pteAddress);
+        auto pte = ensurePTE(m_kernel_page_directory, pteAddress);
         pte.setPhysicalPageBase(pteAddress.get());
         pte.setUserAllowed(false);
         pte.setPresent(false);
@@ -127,7 +133,7 @@ void MemoryManager::identityMap(LinearAddress linearAddress, size_t length)
     // FIXME: ASSERT(linearAddress is 4KB aligned);
     for (dword offset = 0; offset < length; offset += 4096) {
         auto pteAddress = linearAddress.offset(offset);
-        auto pte = ensurePTE(m_pageDirectory, pteAddress);
+        auto pte = ensurePTE(m_kernel_page_directory, pteAddress);
         pte.setPhysicalPageBase(pteAddress.get());
         pte.setUserAllowed(true);
         pte.setPresent(true);
@@ -204,7 +210,7 @@ Vector<PhysicalAddress> MemoryManager::allocatePhysicalPages(size_t count)
 byte* MemoryManager::quickMapOnePage(PhysicalAddress physicalAddress)
 {
     ASSERT_INTERRUPTS_DISABLED();
-    auto pte = ensurePTE(m_pageDirectory, LinearAddress(4 * MB));
+    auto pte = ensurePTE(m_kernel_page_directory, LinearAddress(4 * MB));
     kprintf("MM: quickmap %x @ %x {pte @ %p}\n", physicalAddress.get(), 4*MB, pte.ptr());
     pte.setPhysicalPageBase(physicalAddress.pageBase());
     pte.setPresent(true);
@@ -213,6 +219,20 @@ byte* MemoryManager::quickMapOnePage(PhysicalAddress physicalAddress)
     return (byte*)(4 * MB);
 }
 
+void MemoryManager::enter_kernel_paging_scope()
+{
+    InterruptDisabler disabler;
+    current->m_tss.cr3 = (dword)m_kernel_page_directory;
+    asm volatile("movl %%eax, %%cr3"::"a"(m_kernel_page_directory));
+}
+
+void MemoryManager::enter_task_paging_scope(Task& task)
+{
+    InterruptDisabler disabler;
+    current->m_tss.cr3 = (dword)task.m_pageDirectory;
+    asm volatile("movl %%eax, %%cr3"::"a"(task.m_pageDirectory));
+}
+
 void MemoryManager::flushEntireTLB()
 {
     asm volatile(
@@ -226,6 +246,67 @@ void MemoryManager::flushTLB(LinearAddress laddr)
     asm volatile("invlpg %0": :"m" (*(char*)laddr.get()));
 }
 
+void MemoryManager::map_region_at_address(dword* page_directory, Task::Region& region, LinearAddress laddr)
+{
+    InterruptDisabler disabler;
+    auto& zone = *region.zone;
+    for (size_t i = 0; i < zone.m_pages.size(); ++i) {
+        auto page_laddr = laddr.offset(i * PAGE_SIZE);
+        auto pte = ensurePTE(page_directory, page_laddr);
+        pte.setPhysicalPageBase(zone.m_pages[i].get());
+        pte.setPresent(true);
+        pte.setWritable(true);
+        pte.setUserAllowed(true);
+        flushTLB(page_laddr);
+#ifdef MM_DEBUG
+        dbgprintf("MM: >> map_region_at_address (PD=%x) L%x => P%x\n", page_directory, page_laddr, zone.m_pages[i].get());
+#endif
+    }
+}
+
+void MemoryManager::unmap_range(dword* page_directory, LinearAddress laddr, size_t size)
+{
+    ASSERT((size % PAGE_SIZE) == 0);
+
+    InterruptDisabler disabler;
+    size_t numPages = size / 4096;
+    for (size_t i = 0; i < numPages; ++i) {
+        auto page_laddr = laddr.offset(i * PAGE_SIZE);
+        auto pte = ensurePTE(page_directory, page_laddr);
+        pte.setPhysicalPageBase(0);
+        pte.setPresent(false);
+        pte.setWritable(false);
+        pte.setUserAllowed(false);
+        flushTLB(page_laddr);
+#ifdef MM_DEBUG
+        dbgprintf("MM: << unmap_range L%x =/> 0\n", page_laddr);
+#endif
+    }
+}
+
+LinearAddress MemoryManager::allocate_linear_address_range(size_t size)
+{
+    ASSERT((size % PAGE_SIZE) == 0);
+
+    // FIXME: Recycle ranges!
+    auto laddr = m_next_laddr;
+    m_next_laddr.set(m_next_laddr.get() + size);
+    return laddr;
+}
+
+byte* MemoryManager::create_kernel_alias_for_region(Task::Region& region)
+{
+    InterruptDisabler disabler;
+    auto laddr = allocate_linear_address_range(region.size);
+    map_region_at_address(m_kernel_page_directory, region, laddr);
+    return laddr.asPtr();
+}
+
+void MemoryManager::remove_kernel_alias_for_region(Task::Region& region, byte* addr)
+{
+    unmap_range(m_kernel_page_directory, LinearAddress((dword)addr), region.size);
+}
+
 bool MemoryManager::unmapRegion(Task& task, Task::Region& region)
 {
     InterruptDisabler disabler;
@@ -238,7 +319,9 @@ bool MemoryManager::unmapRegion(Task& task, Task::Region& region)
         pte.setWritable(false);
         pte.setUserAllowed(false);
         flushTLB(laddr);
-        //kprintf("MM: >> Unmapped L%x => P%x <<\n", laddr, zone.m_pages[i].get());
+#ifdef MM_DEBUG
+        //dbgprintf("MM: >> Unmapped L%x => P%x <<\n", laddr, zone.m_pages[i].get());
+#endif
     }
     return true;
 }
@@ -246,7 +329,6 @@ bool MemoryManager::unmapRegion(Task& task, Task::Region& region)
 bool MemoryManager::unmapSubregion(Task& task, Task::Subregion& subregion)
 {
     InterruptDisabler disabler;
-    auto& region = *subregion.region;
     size_t numPages = subregion.size / 4096;
     ASSERT(numPages);
     for (size_t i = 0; i < numPages; ++i) {
@@ -257,7 +339,9 @@ bool MemoryManager::unmapSubregion(Task& task, Task::Subregion& subregion)
         pte.setWritable(false);
         pte.setUserAllowed(false);
         flushTLB(laddr);
-        //kprintf("MM: >> Unmapped subregion %s L%x => P%x <<\n", subregion.name.characters(), laddr, zone.m_pages[i].get());
+#ifdef MM_DEBUG
+        //dbgprintf("MM: >> Unmapped subregion %s L%x => P%x <<\n", subregion.name.characters(), laddr, zone.m_pages[i].get());
+#endif
     }
     return true;
 }
@@ -290,27 +374,18 @@ bool MemoryManager::mapSubregion(Task& task, Task::Subregion& subregion)
         pte.setPhysicalPageBase(zone.m_pages[firstPage + i].get());
         pte.setPresent(true);
         pte.setWritable(true);
-        pte.setUserAllowed(!task.isRing0());
+        pte.setUserAllowed(true);
         flushTLB(laddr);
-        //kprintf("MM: >> Mapped subregion %s L%x => P%x (%u into region)<<\n", subregion.name.characters(), laddr, zone.m_pages[firstPage + i].get(), subregion.offset);
+#ifdef MM_DEBUG
+        //dbgprintf("MM: >> Mapped subregion %s L%x => P%x (%u into region)\n", subregion.name.characters(), laddr, zone.m_pages[firstPage + i].get(), subregion.offset);
+#endif
     }
     return true;
 }
 
 bool MemoryManager::mapRegion(Task& task, Task::Region& region)
 {
-    InterruptDisabler disabler;
-    auto& zone = *region.zone;
-    for (size_t i = 0; i < zone.m_pages.size(); ++i) {
-        auto laddr = region.linearAddress.offset(i * PAGE_SIZE);
-        auto pte = ensurePTE(task.m_pageDirectory,laddr);
-        pte.setPhysicalPageBase(zone.m_pages[i].get());
-        pte.setPresent(true);
-        pte.setWritable(true);
-        pte.setUserAllowed(!task.isRing0()); // FIXME: This doesn't make sense. Allow USER if the TASK is RING0? Wh...what?
-        flushTLB(laddr);
-        //kprintf("MM: >> Mapped L%x => P%x <<\n", laddr, zone.m_pages[i].get());
-    }
+    map_region_at_address(task.m_pageDirectory, region, region.linearAddress);
     return true;
 }
 

Kernel/MemoryManager.h

@@ -41,7 +41,7 @@ class MemoryManager {
 public:
     static MemoryManager& the() PURE;
 
-    PhysicalAddress pageDirectoryBase() const { return PhysicalAddress(reinterpret_cast<dword>(m_pageDirectory)); }
+    PhysicalAddress pageDirectoryBase() const { return PhysicalAddress(reinterpret_cast<dword>(m_kernel_page_directory)); }
 
     static void initialize();
 
@@ -65,12 +65,22 @@ public:
     void registerZone(Zone&);
     void unregisterZone(Zone&);
 
-    void populatePageDirectory(Task&);
+    void populate_page_directory(Task&);
+
+    byte* create_kernel_alias_for_region(Task::Region&);
+    void remove_kernel_alias_for_region(Task::Region&, byte*);
+
+    void enter_kernel_paging_scope();
+    void enter_task_paging_scope(Task&);
 
 private:
     MemoryManager();
     ~MemoryManager();
 
+    LinearAddress allocate_linear_address_range(size_t);
+    void map_region_at_address(dword* page_directory, Task::Region&, LinearAddress);
+    void unmap_range(dword* page_directory, LinearAddress, size_t);
+
     void initializePaging();
     void flushEntireTLB();
     void flushTLB(LinearAddress);
@@ -162,10 +172,12 @@ private:
 
     PageTableEntry ensurePTE(dword* pageDirectory, LinearAddress);
 
-    dword* m_pageDirectory;
+    dword* m_kernel_page_directory;
     dword* m_pageTableZero;
     dword* m_pageTableOne;
 
+    LinearAddress m_next_laddr;
+
     HashTable<Zone*> m_zones;
 
     Vector<PhysicalAddress> m_freePages;

Kernel/ProcFileSystem.cpp

@@ -61,6 +61,7 @@ ByteBuffer procfs$pid_vm(const Task& task)
 ByteBuffer procfs$pid_stack(Task& task)
 {
     InterruptDisabler disabler;
+    ASSERT(false);
     if (current != &task) {
         MM.unmapRegionsForTask(*current);
         MM.mapRegionsForTask(task);

Kernel/Task.cpp

@@ -228,6 +228,11 @@ int Task::sys$spawn(const char* path, const char** args)
     return error;
 }
 
+struct KernelPagingScope {
+    KernelPagingScope() { MM.enter_kernel_paging_scope(); }
+    ~KernelPagingScope() { MM.enter_task_paging_scope(*current); }
+};
+
 Task* Task::createUserTask(const String& path, uid_t uid, gid_t gid, pid_t parentPID, int& error, const char** args, TTY* tty)
 {
     auto parts = path.split('/');
@@ -276,6 +281,7 @@ Task* Task::createUserTask(const String& path, uid_t uid, gid_t gid, pid_t paren
     taskEnvironment.append("HOME=/");
 
     InterruptDisabler disabler; // FIXME: Get rid of this, jesus christ. This "critical" section is HUGE.
+    KernelPagingScope kernelScope;
     Task* t = new Task(parts.takeLast(), uid, gid, parentPID, Ring3, move(cwd), handle->vnode(), tty);
 
     t->m_arguments = move(taskArguments);
@@ -283,20 +289,21 @@ Task* Task::createUserTask(const String& path, uid_t uid, gid_t gid, pid_t paren
 
     ExecSpace space;
     Region* region = nullptr;
+
+    byte* region_alias = nullptr;
+
     space.hookableAlloc = [&] (const String& name, size_t size) {
         if (!size)
             return (void*)nullptr;
-        size = ((size / 4096) + 1) * 4096;
+        size = ((size / 4096) + 1) * 4096; // FIXME: Use ceil_div?
         region = t->allocateRegion(size, String(name));
         ASSERT(region);
-        MM.mapRegion(*t, *region);
-        return (void*)region->linearAddress.asPtr();
+        region_alias = MM.create_kernel_alias_for_region(*region);
+        return (void*)region_alias;
     };
     bool success = space.loadELF(move(elfData));
     if (!success) {
-        // FIXME: This is ugly. If we need to do this, it should be at a different level.
-        MM.unmapRegionsForTask(*t);
-        MM.mapRegionsForTask(*current);
+        MM.remove_kernel_alias_for_region(*region, region_alias);
         delete t;
         kprintf("Failure loading ELF %s\n", path.characters());
         error = -ENOEXEC;
@@ -321,16 +328,15 @@ Task* Task::createUserTask(const String& path, uid_t uid, gid_t gid, pid_t paren
     t->m_tss.eip = (dword)space.symbolPtr("_start");
     if (!t->m_tss.eip) {
         // FIXME: This is ugly. If we need to do this, it should be at a different level.
-        MM.unmapRegionsForTask(*t);
-        MM.mapRegionsForTask(*current);
+        MM.remove_kernel_alias_for_region(*region, region_alias);
         delete t;
         error = -ENOEXEC;
         return nullptr;
     }
 
-    // FIXME: This is ugly. If we need to do this, it should be at a different level.
-    MM.unmapRegionsForTask(*t);
-    MM.mapRegionsForTask(*current);
+    MM.remove_kernel_alias_for_region(*region, region_alias);
+
+    MM.mapRegionsForTask(*t);
 
     s_tasks->prepend(t);
     system.nprocess++;
@@ -409,7 +415,7 @@ Task::Task(String&& name, uid_t uid, gid_t gid, pid_t parentPID, RingLevel ring,
     , m_parentPID(parentPID)
 {
     m_pageDirectory = (dword*)kmalloc_page_aligned(4096);
-    MM.populatePageDirectory(*this);
+    MM.populate_page_directory(*this);
 
     if (tty) {
         m_fileHandles.append(tty->open(O_RDONLY)); // stdin
@@ -421,7 +427,7 @@ Task::Task(String&& name, uid_t uid, gid_t gid, pid_t parentPID, RingLevel ring,
         m_fileHandles.append(nullptr); // stderr
     }
 
-    m_nextRegion = LinearAddress(0x600000);
+    m_nextRegion = LinearAddress(0x10000000);
 
     memset(&m_tss, 0, sizeof(m_tss));
 
@@ -539,8 +545,6 @@ void Task::sys$exit(int status)
 
     setState(Exiting);
 
-    MM.unmapRegionsForTask(*this);
-
     s_tasks->remove(this);
 
     notify_waiters(m_pid, status, 0);
@@ -566,7 +570,6 @@ void Task::murder(int signal)
 
     if (wasCurrent) {
         kprintf("Current task committing suicide!\n");
-        MM.unmapRegionsForTask(*this);
         if (!scheduleNewTask()) {
             kprintf("Task::murder: Failed to schedule a new task :(\n");
             HANG;
@@ -593,8 +596,6 @@ void Task::taskDidCrash(Task* crashedTask)
 
     notify_waiters(crashedTask->m_pid, 0, SIGSEGV);
 
-    MM.unmapRegionsForTask(*crashedTask);
-
     if (!scheduleNewTask()) {
         kprintf("Task::taskDidCrash: Failed to schedule a new task :(\n");
         HANG;
@@ -750,14 +751,8 @@ static bool contextSwitch(Task* t)
         // mark it as runnable for the next round.
         if (current->state() == Task::Running)
             current->setState(Task::Runnable);
-
-        bool success = MM.unmapRegionsForTask(*current);
-        ASSERT(success);
     }
 
-    bool success = MM.mapRegionsForTask(*t);
-    ASSERT(success);
-
     current = t;
     t->setState(Task::Running);
 

Kernel/init.cpp

@@ -29,6 +29,7 @@
 
 #define TEST_VFS
 #define KSYMS
+#define SPAWN_MULTIPLE_SHELLS
 //#define STRESS_TEST_SPAWNING
 //#define TEST_ELF_LOADER
 
@@ -188,9 +189,11 @@ static void init_stage2()
 
     int error;
     auto* sh0 = Task::createUserTask("/bin/sh", (uid_t)100, (gid_t)100, (pid_t)0, error, nullptr, tty0);
+#ifdef SPAWN_MULTIPLE_SHELLS
     auto* sh1 = Task::createUserTask("/bin/sh", (uid_t)100, (gid_t)100, (pid_t)0, error, nullptr, tty1);
     auto* sh2 = Task::createUserTask("/bin/sh", (uid_t)100, (gid_t)100, (pid_t)0, error, nullptr, tty2);
     auto* sh3 = Task::createUserTask("/bin/sh", (uid_t)100, (gid_t)100, (pid_t)0, error, nullptr, tty3);
+#endif
 
 #if 0
     // It would be nice to exit this process, but right now it instantiates all kinds of things.