Implement AllocFrame/FreeFrame

kernel/mem/pmm/allocator/bitmap_allocator.go

@@ -1,6 +1,7 @@
 package allocator
 
 import (
+	"math"
 	"reflect"
 	"unsafe"
 
@@ -17,6 +18,10 @@ var (
 	// primary allocator for reserving pages.
 	FrameAllocator BitmapAllocator
 
+	errBitmapAllocOutOfMemory     = &kernel.Error{Module: "bitmap_alloc", Message: "out of memory"}
+	errBitmapAllocFrameNotManaged = &kernel.Error{Module: "bitmap_alloc", Message: "frame not managed by this allocator"}
+	errBitmapAllocDoubleFree      = &kernel.Error{Module: "bitmap_alloc", Message: "frame is already free"}
+
 	// The followning functions are used by tests to mock calls to the vmm package
 	// and are automatically inlined by the compiler.
 	reserveRegionFn = vmm.EarlyReserveRegion
@@ -238,6 +243,60 @@ func (alloc *BitmapAllocator) printStats() {
 	)
 }
 
+// AllocFrame reserves and returns a physical memory frame. An error will be
+// returned if no more memory can be allocated.
+func (alloc *BitmapAllocator) AllocFrame() (pmm.Frame, *kernel.Error) {
+	for poolIndex := 0; poolIndex < len(alloc.pools); poolIndex++ {
+		if alloc.pools[poolIndex].freeCount == 0 {
+			continue
+		}
+
+		fullBlock := uint64(math.MaxUint64)
+		for blockIndex, block := range alloc.pools[poolIndex].freeBitmap {
+			if block == fullBlock {
+				continue
+			}
+
+			// Block has at least one free slot; we need to scan its bits
+			for blockOffset, mask := 0, uint64(1<<63); mask > 0; blockOffset, mask = blockOffset+1, mask>>1 {
+				if block&mask != 0 {
+					continue
+				}
+
+				alloc.pools[poolIndex].freeCount--
+				alloc.pools[poolIndex].freeBitmap[blockIndex] |= mask
+				alloc.reservedPages++
+				return alloc.pools[poolIndex].startFrame + pmm.Frame((blockIndex<<6)+blockOffset), nil
+			}
+		}
+	}
+
+	return pmm.InvalidFrame, errBitmapAllocOutOfMemory
+}
+
+// FreeFrame releases a frame previously allocated via a call to AllocFrame.
+// Trying to release a frame not part of the allocator pools or a frame that
+// is already marked as free will cause an error to be returned.
+func (alloc *BitmapAllocator) FreeFrame(frame pmm.Frame) *kernel.Error {
+	poolIndex := alloc.poolForFrame(frame)
+	if poolIndex < 0 {
+		return errBitmapAllocFrameNotManaged
+	}
+
+	relFrame := frame - alloc.pools[poolIndex].startFrame
+	block := relFrame >> 6
+	mask := uint64(1 << (63 - (relFrame - block<<6)))
+
+	if alloc.pools[poolIndex].freeBitmap[block]&mask == 0 {
+		return errBitmapAllocDoubleFree
+	}
+
+	alloc.pools[poolIndex].freeBitmap[block] &^= mask
+	alloc.pools[poolIndex].freeCount++
+	alloc.reservedPages--
+	return nil
+}
+
 // earlyAllocFrame is a helper that delegates a frame allocation request to the
 // early allocator instance. This function is passed as an argument to
 // vmm.SetFrameAllocator instead of earlyAllocator.AllocFrame. The latter

kernel/mem/pmm/allocator/bitmap_allocator_test.go

@@ -313,6 +313,80 @@ func TestBitmapAllocatorReserveEarlyAllocatorFrames(t *testing.T) {
 	}
 }
 
+func TestBitmapAllocatorAllocAndFreeFrame(t *testing.T) {
+	var alloc = BitmapAllocator{
+		pools: []framePool{
+			{
+				startFrame: pmm.Frame(0),
+				endFrame:   pmm.Frame(7),
+				freeCount:  8,
+				// only the first 8 bits of block 0 are used
+				freeBitmap: make([]uint64, 1),
+			},
+			{
+				startFrame: pmm.Frame(64),
+				endFrame:   pmm.Frame(191),
+				freeCount:  128,
+				freeBitmap: make([]uint64, 2),
+			},
+		},
+		totalPages: 136,
+	}
+
+	// Test Alloc
+	for poolIndex, pool := range alloc.pools {
+		for expFrame := pool.startFrame; expFrame <= pool.endFrame; expFrame++ {
+			got, err := alloc.AllocFrame()
+			if err != nil {
+				t.Fatalf("[pool %d] unexpected error: %v", err)
+			}
+
+			if got != expFrame {
+				t.Errorf("[pool %d] expected allocated frame to be %d; got %d", poolIndex, expFrame, got)
+			}
+		}
+
+		if alloc.pools[poolIndex].freeCount != 0 {
+			t.Errorf("[pool %d] expected free count to be 0; got %d", poolIndex, alloc.pools[poolIndex].freeCount)
+		}
+	}
+
+	if alloc.reservedPages != alloc.totalPages {
+		t.Errorf("expected reservedPages to match totalPages(%d); got %d", alloc.totalPages, alloc.reservedPages)
+	}
+
+	if _, err := alloc.AllocFrame(); err != errBitmapAllocOutOfMemory {
+		t.Fatalf("expected error errBitmapAllocOutOfMemory; got %v", err)
+	}
+
+	// Test Free
+	expFreeCount := []uint32{8, 128}
+	for poolIndex, pool := range alloc.pools {
+		for frame := pool.startFrame; frame <= pool.endFrame; frame++ {
+			if err := alloc.FreeFrame(frame); err != nil {
+				t.Fatalf("[pool %d] unexpected error: %v", err)
+			}
+		}
+
+		if alloc.pools[poolIndex].freeCount != expFreeCount[poolIndex] {
+			t.Errorf("[pool %d] expected free count to be %d; got %d", poolIndex, expFreeCount[poolIndex], alloc.pools[poolIndex].freeCount)
+		}
+	}
+
+	if alloc.reservedPages != 0 {
+		t.Errorf("expected reservedPages to be 0; got %d", alloc.reservedPages)
+	}
+
+	// Test Free errors
+	if err := alloc.FreeFrame(pmm.Frame(0)); err != errBitmapAllocDoubleFree {
+		t.Fatalf("expected error errBitmapAllocDoubleFree; got %v", err)
+	}
+
+	if err := alloc.FreeFrame(pmm.Frame(0xbadf00d)); err != errBitmapAllocFrameNotManaged {
+		t.Fatalf("expected error errBitmapFrameNotManaged; got %v", err)
+	}
+}
+
 func TestAllocatorPackageInit(t *testing.T) {
 	defer func() {
 		mapFn = vmm.Map