1 files changed, 265 insertions, 0 deletions
diff --git a/pkg/ring0/pagetables/walker_empty_amd64.go b/pkg/ring0/pagetables/walker_empty_amd64.go
new file mode 100644
index 000000000..a3cd7a1a2
--- /dev/null
+++ b/pkg/ring0/pagetables/walker_empty_amd64.go
@@ -0,0 +1,265 @@
+// +build amd64
+
+package pagetables
+
+// iterateRangeCanonical walks a canonical range.
+//
+//go:nosplit
+func (w *emptyWalker) iterateRangeCanonical(start, end uintptr) bool {
+	for pgdIndex := uint16((start & pgdMask) >> pgdShift); start < end && pgdIndex < entriesPerPage; pgdIndex++ {
+		var (
+			pgdEntry   = &w.pageTables.root[pgdIndex]
+			pudEntries *PTEs
+		)
+		if !pgdEntry.Valid() {
+			if !w.visitor.requiresAlloc() {
+
+				start = emptynext(start, pgdSize)
+				continue
+			}
+
+			pudEntries = w.pageTables.Allocator.NewPTEs()
+			pgdEntry.setPageTable(w.pageTables, pudEntries)
+		} else {
+			pudEntries = w.pageTables.Allocator.LookupPTEs(pgdEntry.Address())
+		}
+
+		clearPUDEntries := uint16(0)
+
+		for pudIndex := uint16((start & pudMask) >> pudShift); start < end && pudIndex < entriesPerPage; pudIndex++ {
+			var (
+				pudEntry   = &pudEntries[pudIndex]
+				pmdEntries *PTEs
+			)
+			if !pudEntry.Valid() {
+				if !w.visitor.requiresAlloc() {
+
+					clearPUDEntries++
+					start = emptynext(start, pudSize)
+					continue
+				}
+
+				if start&(pudSize-1) == 0 && end-start >= pudSize {
+					pudEntry.SetSuper()
+					if !w.visitor.visit(uintptr(start&^(pudSize-1)), pudEntry, pudSize-1) {
+						return false
+					}
+					if pudEntry.Valid() {
+						start = emptynext(start, pudSize)
+						continue
+					}
+				}
+
+				pmdEntries = w.pageTables.Allocator.NewPTEs()
+				pudEntry.setPageTable(w.pageTables, pmdEntries)
+
+			} else if pudEntry.IsSuper() {
+
+				if w.visitor.requiresSplit() && (start&(pudSize-1) != 0 || end < emptynext(start, pudSize)) {
+
+					pmdEntries = w.pageTables.Allocator.NewPTEs()
+					for index := uint16(0); index < entriesPerPage; index++ {
+						pmdEntries[index].SetSuper()
+						pmdEntries[index].Set(
+							pudEntry.Address()+(pmdSize*uintptr(index)),
+							pudEntry.Opts())
+					}
+					pudEntry.setPageTable(w.pageTables, pmdEntries)
+				} else {
+
+					if !w.visitor.visit(uintptr(start&^(pudSize-1)), pudEntry, pudSize-1) {
+						return false
+					}
+
+					if !pudEntry.Valid() {
+						clearPUDEntries++
+					}
+
+					start = emptynext(start, pudSize)
+					continue
+				}
+			} else {
+				pmdEntries = w.pageTables.Allocator.LookupPTEs(pudEntry.Address())
+			}
+
+			clearPMDEntries := uint16(0)
+
+			for pmdIndex := uint16((start & pmdMask) >> pmdShift); start < end && pmdIndex < entriesPerPage; pmdIndex++ {
+				var (
+					pmdEntry   = &pmdEntries[pmdIndex]
+					pteEntries *PTEs
+				)
+				if !pmdEntry.Valid() {
+					if !w.visitor.requiresAlloc() {
+
+						clearPMDEntries++
+						start = emptynext(start, pmdSize)
+						continue
+					}
+
+					if start&(pmdSize-1) == 0 && end-start >= pmdSize {
+						pmdEntry.SetSuper()
+						if !w.visitor.visit(uintptr(start&^(pmdSize-1)), pmdEntry, pmdSize-1) {
+							return false
+						}
+						if pmdEntry.Valid() {
+							start = emptynext(start, pmdSize)
+							continue
+						}
+					}
+
+					pteEntries = w.pageTables.Allocator.NewPTEs()
+					pmdEntry.setPageTable(w.pageTables, pteEntries)
+
+				} else if pmdEntry.IsSuper() {
+
+					if w.visitor.requiresSplit() && (start&(pmdSize-1) != 0 || end < emptynext(start, pmdSize)) {
+
+						pteEntries = w.pageTables.Allocator.NewPTEs()
+						for index := uint16(0); index < entriesPerPage; index++ {
+							pteEntries[index].Set(
+								pmdEntry.Address()+(pteSize*uintptr(index)),
+								pmdEntry.Opts())
+						}
+						pmdEntry.setPageTable(w.pageTables, pteEntries)
+					} else {
+
+						if !w.visitor.visit(uintptr(start&^(pmdSize-1)), pmdEntry, pmdSize-1) {
+							return false
+						}
+
+						if !pmdEntry.Valid() {
+							clearPMDEntries++
+						}
+
+						start = emptynext(start, pmdSize)
+						continue
+					}
+				} else {
+					pteEntries = w.pageTables.Allocator.LookupPTEs(pmdEntry.Address())
+				}
+
+				clearPTEEntries := uint16(0)
+
+				for pteIndex := uint16((start & pteMask) >> pteShift); start < end && pteIndex < entriesPerPage; pteIndex++ {
+					var (
+						pteEntry = &pteEntries[pteIndex]
+					)
+					if !pteEntry.Valid() && !w.visitor.requiresAlloc() {
+						clearPTEEntries++
+						start += pteSize
+						continue
+					}
+
+					if !w.visitor.visit(uintptr(start&^(pteSize-1)), pteEntry, pteSize-1) {
+						return false
+					}
+					if !pteEntry.Valid() && !w.visitor.requiresAlloc() {
+						clearPTEEntries++
+					}
+
+					start += pteSize
+					continue
+				}
+
+				if clearPTEEntries == entriesPerPage {
+					pmdEntry.Clear()
+					w.pageTables.Allocator.FreePTEs(pteEntries)
+					clearPMDEntries++
+				}
+			}
+
+			if clearPMDEntries == entriesPerPage {
+				pudEntry.Clear()
+				w.pageTables.Allocator.FreePTEs(pmdEntries)
+				clearPUDEntries++
+			}
+		}
+
+		if clearPUDEntries == entriesPerPage {
+			pgdEntry.Clear()
+			w.pageTables.Allocator.FreePTEs(pudEntries)
+		}
+	}
+	return true
+}
+
+// Walker walks page tables.
+type emptyWalker struct {
+	// pageTables are the tables to walk.
+	pageTables *PageTables
+
+	// Visitor is the set of arguments.
+	visitor emptyVisitor
+}
+
+// iterateRange iterates over all appropriate levels of page tables for the given range.
+//
+// If requiresAlloc is true, then Set _must_ be called on all given PTEs. The
+// exception is super pages. If a valid super page (huge or jumbo) cannot be
+// installed, then the walk will continue to individual entries.
+//
+// This algorithm will attempt to maximize the use of super/sect pages whenever
+// possible. Whether a super page is provided will be clear through the range
+// provided in the callback.
+//
+// Note that if requiresAlloc is true, then no gaps will be present. However,
+// if alloc is not set, then the iteration will likely be full of gaps.
+//
+// Note that this function should generally be avoided in favor of Map, Unmap,
+// etc. when not necessary.
+//
+// Precondition: start must be page-aligned.
+// Precondition: start must be less than end.
+// Precondition: If requiresAlloc is true, then start and end should not span
+// non-canonical ranges. If they do, a panic will result.
+//
+//go:nosplit
+func (w *emptyWalker) iterateRange(start, end uintptr) {
+	if start%pteSize != 0 {
+		panic("unaligned start")
+	}
+	if end < start {
+		panic("start > end")
+	}
+	if start < lowerTop {
+		if end <= lowerTop {
+			w.iterateRangeCanonical(start, end)
+		} else if end > lowerTop && end <= upperBottom {
+			if w.visitor.requiresAlloc() {
+				panic("alloc spans non-canonical range")
+			}
+			w.iterateRangeCanonical(start, lowerTop)
+		} else {
+			if w.visitor.requiresAlloc() {
+				panic("alloc spans non-canonical range")
+			}
+			if !w.iterateRangeCanonical(start, lowerTop) {
+				return
+			}
+			w.iterateRangeCanonical(upperBottom, end)
+		}
+	} else if start < upperBottom {
+		if end <= upperBottom {
+			if w.visitor.requiresAlloc() {
+				panic("alloc spans non-canonical range")
+			}
+		} else {
+			if w.visitor.requiresAlloc() {
+				panic("alloc spans non-canonical range")
+			}
+			w.iterateRangeCanonical(upperBottom, end)
+		}
+	} else {
+		w.iterateRangeCanonical(start, end)
+	}
+}
+
+// next returns the next address quantized by the given size.
+//
+//go:nosplit
+func emptynext(start uintptr, size uintptr) uintptr {
+	start &= ^(size - 1)
+	start += size
+	return start
+}