Define PageDirectoryTable and helpers that support inactive tables

The Map/Unmap methods of PageDirectoryTable operate similar to the
global Map/Unmap functions. While the global functions work with the
currently active PDT, the PageDirectoryTable methods can also
work with inactive page tables by temporarily modifying the recursive
mapping of the active PDT to point to the inactive PDT frame before
delegating the mapping/unmapping to the global Map/Unmap functions.

kernel/mem/vmm/pdt.go

@@ -0,0 +1,135 @@
+package vmm
+
+import (
+	"unsafe"
+
+	"github.com/achilleasa/gopher-os/kernel"
+	"github.com/achilleasa/gopher-os/kernel/mem"
+	"github.com/achilleasa/gopher-os/kernel/mem/pmm"
+)
+
+var (
+	// activePDTFn is used by tests to override calls to activePDT which
+	// will cause a fault if called in user-mode.
+	activePDTFn = activePDT
+
+	// switchPDTFn is used by tests to override calls to switchPDT which
+	// will cause a fault if called in user-mode.
+	switchPDTFn = switchPDT
+
+	// mapFn is used by tests and is automatically inlined by the compiler.
+	mapFn = Map
+
+	// mapTemporaryFn is used by tests and is automatically inlined by the compiler.
+	mapTemporaryFn = MapTemporary
+
+	// unmapmFn is used by tests and is automatically inlined by the compiler.
+	unmapFn = Unmap
+)
+
+// PageDirectoryTable describes the top-most table in a multi-level paging scheme.
+type PageDirectoryTable struct {
+	pdtFrame pmm.Frame
+}
+
+// Init sets up the page table directory starting at the supplied physical
+// address. If the supplied frame does not match the currently active PDT, then
+// Init assumes that this is a new page table directory that needs
+// bootstapping. In such a case, a temporary mapping is established so that
+// Init can:
+//  - call mem.Memset to clear the frame contents
+//  - setup a recursive mapping for the last table entry to the page itself.
+func (pdt *PageDirectoryTable) Init(pdtFrame pmm.Frame, allocFn FrameAllocator) *kernel.Error {
+	pdt.pdtFrame = pdtFrame
+
+	// Check active PDT physical address. If it matches the input pdt then
+	// nothing more needs to be done
+	activePdtAddr := activePDTFn()
+	if pdtFrame.Address() == activePdtAddr {
+		return nil
+	}
+
+	// Create a temporary mapping for the pdt frame so we can work on it
+	pdtPage, err := mapTemporaryFn(pdtFrame, allocFn)
+	if err != nil {
+		return err
+	}
+
+	// Clear the page contents and setup recursive mapping for the last PDT entry
+	mem.Memset(pdtPage.Address(), 0, mem.PageSize)
+	lastPdtEntry := (*pageTableEntry)(unsafe.Pointer(pdtPage.Address() + (((1 << pageLevelBits[0]) - 1) << mem.PointerShift)))
+	*lastPdtEntry = 0
+	lastPdtEntry.SetFlags(FlagPresent | FlagRW)
+	lastPdtEntry.SetFrame(pdtFrame)
+
+	// Remove temporary mapping
+	unmapFn(pdtPage)
+
+	return nil
+}
+
+// Map establishes a mapping between a virtual page and a physical memory frame
+// using this PDT. This method behaves in a similar fashion to the global Map()
+// function with the difference that it also supports inactive page PDTs by
+// establishing a temporary mapping so that Map() can access the inactive PDT
+// entries.
+func (pdt PageDirectoryTable) Map(page Page, frame pmm.Frame, flags PageTableEntryFlag, allocFn FrameAllocator) *kernel.Error {
+	var (
+		activePdtFrame   = pmm.Frame(activePDTFn() >> mem.PageShift)
+		lastPdtEntryAddr uintptr
+		lastPdtEntry     *pageTableEntry
+	)
+	// If this table is not active we need to temporarily map it to the
+	// last entry in the active PDT so we can access it using the recursive
+	// virtual address scheme.
+	if activePdtFrame != pdt.pdtFrame {
+		lastPdtEntryAddr = activePdtFrame.Address() + (((1 << pageLevelBits[0]) - 1) << mem.PointerShift)
+		lastPdtEntry = (*pageTableEntry)(unsafe.Pointer(lastPdtEntryAddr))
+		lastPdtEntry.SetFrame(pdt.pdtFrame)
+		flushTLBEntryFn(lastPdtEntryAddr)
+	}
+
+	err := mapFn(page, frame, flags, allocFn)
+
+	if activePdtFrame != pdt.pdtFrame {
+		lastPdtEntry.SetFrame(activePdtFrame)
+		flushTLBEntryFn(lastPdtEntryAddr)
+	}
+
+	return err
+}
+
+// Unmap removes a mapping previousle installed by a call to Map() on this PDT.
+// This method behaves in a similar fashion to the global Unmap() function with
+// the difference that it also supports inactive page PDTs by establishing a
+// temporary mapping so that Unmap() can access the inactive PDT entries.
+func (pdt PageDirectoryTable) Unmap(page Page) *kernel.Error {
+	var (
+		activePdtFrame   = pmm.Frame(activePDTFn() >> mem.PageShift)
+		lastPdtEntryAddr uintptr
+		lastPdtEntry     *pageTableEntry
+	)
+	// If this table is not active we need to temporarily map it to the
+	// last entry in the active PDT so we can access it using the recursive
+	// virtual address scheme.
+	if activePdtFrame != pdt.pdtFrame {
+		lastPdtEntryAddr = activePdtFrame.Address() + (((1 << pageLevelBits[0]) - 1) << mem.PointerShift)
+		lastPdtEntry = (*pageTableEntry)(unsafe.Pointer(lastPdtEntryAddr))
+		lastPdtEntry.SetFrame(pdt.pdtFrame)
+		flushTLBEntryFn(lastPdtEntryAddr)
+	}
+
+	err := unmapFn(page)
+
+	if activePdtFrame != pdt.pdtFrame {
+		lastPdtEntry.SetFrame(activePdtFrame)
+		flushTLBEntryFn(lastPdtEntryAddr)
+	}
+
+	return err
+}
+
+// Activate enables this page directory table and flushes the TLB
+func (pdt PageDirectoryTable) Activate() {
+	switchPDTFn(pdt.pdtFrame.Address())
+}

kernel/mem/vmm/pdt_test.go

@@ -0,0 +1,331 @@
+package vmm
+
+import (
+	"runtime"
+	"testing"
+	"unsafe"
+
+	"github.com/achilleasa/gopher-os/kernel"
+	"github.com/achilleasa/gopher-os/kernel/mem"
+	"github.com/achilleasa/gopher-os/kernel/mem/pmm"
+)
+
+func TestPageDirectoryTableInitAmd64(t *testing.T) {
+	if runtime.GOARCH != "amd64" {
+		t.Skip("test requires amd64 runtime; skipping")
+	}
+
+	defer func(origFlushTLBEntry func(uintptr), origActivePDT func() uintptr, origMapTemporary func(pmm.Frame, FrameAllocator) (Page, *kernel.Error), origUnmap func(Page) *kernel.Error) {
+		flushTLBEntryFn = origFlushTLBEntry
+		activePDTFn = origActivePDT
+		mapTemporaryFn = origMapTemporary
+		unmapFn = origUnmap
+	}(flushTLBEntryFn, activePDTFn, mapTemporaryFn, unmapFn)
+
+	t.Run("already mapped PDT", func(t *testing.T) {
+		var (
+			pdt      PageDirectoryTable
+			pdtFrame = pmm.Frame(123)
+		)
+
+		activePDTFn = func() uintptr {
+			return pdtFrame.Address()
+		}
+
+		mapTemporaryFn = func(_ pmm.Frame, _ FrameAllocator) (Page, *kernel.Error) {
+			t.Fatal("unexpected call to MapTemporary")
+			return 0, nil
+		}
+
+		unmapFn = func(_ Page) *kernel.Error {
+			t.Fatal("unexpected call to Unmap")
+			return nil
+		}
+
+		if err := pdt.Init(pdtFrame, nil); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	t.Run("not mapped PDT", func(t *testing.T) {
+		var (
+			pdt      PageDirectoryTable
+			pdtFrame = pmm.Frame(123)
+			physPage [mem.PageSize >> mem.PointerShift]pageTableEntry
+		)
+
+		// Fill phys page with random junk
+		mem.Memset(uintptr(unsafe.Pointer(&physPage[0])), 0xf0, mem.PageSize)
+
+		activePDTFn = func() uintptr {
+			return 0
+		}
+
+		mapTemporaryFn = func(_ pmm.Frame, _ FrameAllocator) (Page, *kernel.Error) {
+			return PageFromAddress(uintptr(unsafe.Pointer(&physPage[0]))), nil
+		}
+
+		flushTLBEntryFn = func(_ uintptr) {}
+
+		unmapCallCount := 0
+		unmapFn = func(_ Page) *kernel.Error {
+			unmapCallCount++
+			return nil
+		}
+
+		if err := pdt.Init(pdtFrame, nil); err != nil {
+			t.Fatal(err)
+		}
+
+		if unmapCallCount != 1 {
+			t.Fatalf("expected Unmap to be called 1 time; called %d", unmapCallCount)
+		}
+
+		for i := 0; i < len(physPage)-1; i++ {
+			if physPage[i] != 0 {
+				t.Errorf("expected PDT entry %d to be cleared; got %x", i, physPage[i])
+			}
+		}
+
+		// The last page should be recursively mapped to the PDT
+		lastPdtEntry := physPage[len(physPage)-1]
+		if !lastPdtEntry.HasFlags(FlagPresent | FlagRW) {
+			t.Fatal("expected last PDT entry to have FlagPresent and FlagRW set")
+		}
+
+		if lastPdtEntry.Frame() != pdtFrame {
+			t.Fatalf("expected last PDT entry to be recursively mapped to physical frame %x; got %x", pdtFrame, lastPdtEntry.Frame())
+		}
+	})
+
+	t.Run("temporary mapping failure", func(t *testing.T) {
+		var (
+			pdt      PageDirectoryTable
+			pdtFrame = pmm.Frame(123)
+		)
+
+		activePDTFn = func() uintptr {
+			return 0
+		}
+
+		expErr := &kernel.Error{Module: "test", Message: "error mapping page"}
+
+		mapTemporaryFn = func(_ pmm.Frame, _ FrameAllocator) (Page, *kernel.Error) {
+			return 0, expErr
+		}
+
+		unmapFn = func(_ Page) *kernel.Error {
+			t.Fatal("unexpected call to Unmap")
+			return nil
+		}
+
+		if err := pdt.Init(pdtFrame, nil); err != expErr {
+			t.Fatalf("expected to get error: %v; got %v", *expErr, err)
+		}
+	})
+}
+
+func TestPageDirectoryTableMapAmd64(t *testing.T) {
+	if runtime.GOARCH != "amd64" {
+		t.Skip("test requires amd64 runtime; skipping")
+	}
+
+	defer func(origFlushTLBEntry func(uintptr), origActivePDT func() uintptr, origMap func(Page, pmm.Frame, PageTableEntryFlag, FrameAllocator) *kernel.Error) {
+		flushTLBEntryFn = origFlushTLBEntry
+		activePDTFn = origActivePDT
+		mapFn = origMap
+	}(flushTLBEntryFn, activePDTFn, mapFn)
+
+	t.Run("already mapped PDT", func(t *testing.T) {
+		var (
+			pdtFrame = pmm.Frame(123)
+			pdt      = PageDirectoryTable{pdtFrame: pdtFrame}
+			page     = PageFromAddress(uintptr(100 * mem.Mb))
+		)
+
+		activePDTFn = func() uintptr {
+			return pdtFrame.Address()
+		}
+
+		mapFn = func(_ Page, _ pmm.Frame, _ PageTableEntryFlag, _ FrameAllocator) *kernel.Error {
+			return nil
+		}
+
+		flushCallCount := 0
+		flushTLBEntryFn = func(_ uintptr) {
+			flushCallCount++
+		}
+
+		if err := pdt.Map(page, pmm.Frame(321), FlagRW, nil); err != nil {
+			t.Fatal(err)
+		}
+
+		if exp := 0; flushCallCount != exp {
+			t.Fatalf("expected flushTLBEntry to be called %d times; called %d", exp, flushCallCount)
+		}
+	})
+
+	t.Run("not mapped PDT", func(t *testing.T) {
+		var (
+			pdtFrame       = pmm.Frame(123)
+			pdt            = PageDirectoryTable{pdtFrame: pdtFrame}
+			page           = PageFromAddress(uintptr(100 * mem.Mb))
+			activePhysPage [mem.PageSize >> mem.PointerShift]pageTableEntry
+			activePdtFrame = pmm.Frame(uintptr(unsafe.Pointer(&activePhysPage[0])) >> mem.PageShift)
+		)
+
+		// Initially, activePhysPage is recursively mapped to itself
+		activePhysPage[len(activePhysPage)-1].SetFlags(FlagPresent | FlagRW)
+		activePhysPage[len(activePhysPage)-1].SetFrame(activePdtFrame)
+
+		activePDTFn = func() uintptr {
+			return activePdtFrame.Address()
+		}
+
+		mapFn = func(_ Page, _ pmm.Frame, _ PageTableEntryFlag, _ FrameAllocator) *kernel.Error {
+			return nil
+		}
+
+		flushCallCount := 0
+		flushTLBEntryFn = func(_ uintptr) {
+			switch flushCallCount {
+			case 0:
+				// the first time we flush the tlb entry, the last entry of
+				// the active pdt should be pointing to pdtFrame
+				if got := activePhysPage[len(activePhysPage)-1].Frame(); got != pdtFrame {
+					t.Fatalf("expected last PDT entry of active PDT to be re-mapped to frame %x; got %x", pdtFrame, got)
+				}
+			case 1:
+				// the second time we flush the tlb entry, the last entry of
+				// the active pdt should be pointing back to activePdtFrame
+				if got := activePhysPage[len(activePhysPage)-1].Frame(); got != activePdtFrame {
+					t.Fatalf("expected last PDT entry of active PDT to be mapped back frame %x; got %x", activePdtFrame, got)
+				}
+			}
+			flushCallCount++
+		}
+
+		if err := pdt.Map(page, pmm.Frame(321), FlagRW, nil); err != nil {
+			t.Fatal(err)
+		}
+
+		if exp := 2; flushCallCount != exp {
+			t.Fatalf("expected flushTLBEntry to be called %d times; called %d", exp, flushCallCount)
+		}
+	})
+}
+
+func TestPageDirectoryTableUnmapAmd64(t *testing.T) {
+	if runtime.GOARCH != "amd64" {
+		t.Skip("test requires amd64 runtime; skipping")
+	}
+
+	defer func(origFlushTLBEntry func(uintptr), origActivePDT func() uintptr, origUnmap func(Page) *kernel.Error) {
+		flushTLBEntryFn = origFlushTLBEntry
+		activePDTFn = origActivePDT
+		unmapFn = origUnmap
+	}(flushTLBEntryFn, activePDTFn, unmapFn)
+
+	t.Run("already mapped PDT", func(t *testing.T) {
+		var (
+			pdtFrame = pmm.Frame(123)
+			pdt      = PageDirectoryTable{pdtFrame: pdtFrame}
+			page     = PageFromAddress(uintptr(100 * mem.Mb))
+		)
+
+		activePDTFn = func() uintptr {
+			return pdtFrame.Address()
+		}
+
+		unmapFn = func(_ Page) *kernel.Error {
+			return nil
+		}
+
+		flushCallCount := 0
+		flushTLBEntryFn = func(_ uintptr) {
+			flushCallCount++
+		}
+
+		if err := pdt.Unmap(page); err != nil {
+			t.Fatal(err)
+		}
+
+		if exp := 0; flushCallCount != exp {
+			t.Fatalf("expected flushTLBEntry to be called %d times; called %d", exp, flushCallCount)
+		}
+	})
+
+	t.Run("not mapped PDT", func(t *testing.T) {
+		var (
+			pdtFrame       = pmm.Frame(123)
+			pdt            = PageDirectoryTable{pdtFrame: pdtFrame}
+			page           = PageFromAddress(uintptr(100 * mem.Mb))
+			activePhysPage [mem.PageSize >> mem.PointerShift]pageTableEntry
+			activePdtFrame = pmm.Frame(uintptr(unsafe.Pointer(&activePhysPage[0])) >> mem.PageShift)
+		)
+
+		// Initially, activePhysPage is recursively mapped to itself
+		activePhysPage[len(activePhysPage)-1].SetFlags(FlagPresent | FlagRW)
+		activePhysPage[len(activePhysPage)-1].SetFrame(activePdtFrame)
+
+		activePDTFn = func() uintptr {
+			return activePdtFrame.Address()
+		}
+
+		unmapFn = func(_ Page) *kernel.Error {
+			return nil
+		}
+
+		flushCallCount := 0
+		flushTLBEntryFn = func(_ uintptr) {
+			switch flushCallCount {
+			case 0:
+				// the first time we flush the tlb entry, the last entry of
+				// the active pdt should be pointing to pdtFrame
+				if got := activePhysPage[len(activePhysPage)-1].Frame(); got != pdtFrame {
+					t.Fatalf("expected last PDT entry of active PDT to be re-mapped to frame %x; got %x", pdtFrame, got)
+				}
+			case 1:
+				// the second time we flush the tlb entry, the last entry of
+				// the active pdt should be pointing back to activePdtFrame
+				if got := activePhysPage[len(activePhysPage)-1].Frame(); got != activePdtFrame {
+					t.Fatalf("expected last PDT entry of active PDT to be mapped back frame %x; got %x", activePdtFrame, got)
+				}
+			}
+			flushCallCount++
+		}
+
+		if err := pdt.Unmap(page); err != nil {
+			t.Fatal(err)
+		}
+
+		if exp := 2; flushCallCount != exp {
+			t.Fatalf("expected flushTLBEntry to be called %d times; called %d", exp, flushCallCount)
+		}
+	})
+}
+
+func TestPageDirectoryTableActivateAmd64(t *testing.T) {
+	if runtime.GOARCH != "amd64" {
+		t.Skip("test requires amd64 runtime; skipping")
+	}
+
+	defer func(origSwitchPDT func(uintptr)) {
+		switchPDTFn = origSwitchPDT
+	}(switchPDTFn)
+
+	var (
+		pdtFrame = pmm.Frame(123)
+		pdt      = PageDirectoryTable{pdtFrame: pdtFrame}
+	)
+
+	switchPDTCallCount := 0
+	switchPDTFn = func(_ uintptr) {
+		switchPDTCallCount++
+	}
+
+	pdt.Activate()
+	if exp := 1; switchPDTCallCount != exp {
+		t.Fatalf("expected switchPDT to be called %d times; called %d", exp, switchPDTCallCount)
+	}
+}