111 lines
3.3 KiB
Go
111 lines
3.3 KiB
Go
// Copyright 2018 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package pagetables
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// Visitor is a generic type.
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type Visitor interface {
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// visit is called on each PTE. The returned boolean indicates whether
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// the walk should continue.
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visit(start uintptr, pte *PTE, align uintptr) bool
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// requiresAlloc indicates that new entries should be allocated within
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// the walked range.
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requiresAlloc() bool
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// requiresSplit indicates that entries in the given range should be
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// split if they are huge or jumbo pages.
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requiresSplit() bool
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}
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// Walker walks page tables.
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type Walker struct {
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// pageTables are the tables to walk.
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pageTables *PageTables
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// Visitor is the set of arguments.
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visitor Visitor
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}
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// iterateRange iterates over all appropriate levels of page tables for the given range.
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//
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// If requiresAlloc is true, then Set _must_ be called on all given PTEs. The
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// exception is super pages. If a valid super page (huge or jumbo) cannot be
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// installed, then the walk will continue to individual entries.
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//
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// This algorithm will attempt to maximize the use of super/sect pages whenever
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// possible. Whether a super page is provided will be clear through the range
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// provided in the callback.
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//
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// Note that if requiresAlloc is true, then no gaps will be present. However,
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// if alloc is not set, then the iteration will likely be full of gaps.
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//
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// Note that this function should generally be avoided in favor of Map, Unmap,
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// etc. when not necessary.
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//
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// Precondition: start must be page-aligned.
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// Precondition: start must be less than end.
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// Precondition: If requiresAlloc is true, then start and end should not span
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// non-canonical ranges. If they do, a panic will result.
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//
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//go:nosplit
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func (w *Walker) iterateRange(start, end uintptr) {
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if start%pteSize != 0 {
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panic("unaligned start")
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}
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if end < start {
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panic("start > end")
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}
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if start < lowerTop {
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if end <= lowerTop {
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w.iterateRangeCanonical(start, end)
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} else if end > lowerTop && end <= upperBottom {
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if w.visitor.requiresAlloc() {
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panic("alloc spans non-canonical range")
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}
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w.iterateRangeCanonical(start, lowerTop)
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} else {
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if w.visitor.requiresAlloc() {
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panic("alloc spans non-canonical range")
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}
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if !w.iterateRangeCanonical(start, lowerTop) {
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return
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}
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w.iterateRangeCanonical(upperBottom, end)
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}
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} else if start < upperBottom {
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if end <= upperBottom {
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if w.visitor.requiresAlloc() {
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panic("alloc spans non-canonical range")
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}
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} else {
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if w.visitor.requiresAlloc() {
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panic("alloc spans non-canonical range")
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}
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w.iterateRangeCanonical(upperBottom, end)
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}
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} else {
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w.iterateRangeCanonical(start, end)
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}
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}
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// next returns the next address quantized by the given size.
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//
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//go:nosplit
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func next(start uintptr, size uintptr) uintptr {
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start &= ^(size - 1)
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start += size
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return start
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}
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