292 lines
8.3 KiB
Go
292 lines
8.3 KiB
Go
// Copyright 2018 Google Inc.
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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 kvm
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import (
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"reflect"
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"sync"
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"sync/atomic"
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"gvisor.googlesource.com/gvisor/pkg/atomicbitops"
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"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
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"gvisor.googlesource.com/gvisor/pkg/sentry/platform/filemem"
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"gvisor.googlesource.com/gvisor/pkg/sentry/platform/ring0/pagetables"
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"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
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)
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type vCPUBitArray [(_KVM_NR_VCPUS + 63) / 64]uint64
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// dirtySet tracks vCPUs for invalidation.
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type dirtySet struct {
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vCPUs vCPUBitArray
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}
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// forEach iterates over all CPUs in the dirty set.
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func (ds *dirtySet) forEach(m *machine, fn func(c *vCPU)) {
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var localSet vCPUBitArray
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for index := 0; index < len(ds.vCPUs); index++ {
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// Clear the dirty set, copy to the local one.
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localSet[index] = atomic.SwapUint64(&ds.vCPUs[index], 0)
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}
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m.mu.RLock()
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defer m.mu.RUnlock()
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for _, c := range m.vCPUs {
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index := uint64(c.id) / 64
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bit := uint64(1) << uint(c.id%64)
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// Call the function if it was set.
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if localSet[index]&bit != 0 {
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fn(c)
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}
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}
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}
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// mark marks the given vCPU as dirty and returns whether it was previously
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// clean. Being previously clean implies that a flush is needed on entry.
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func (ds *dirtySet) mark(c *vCPU) bool {
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index := uint64(c.id) / 64
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bit := uint64(1) << uint(c.id%64)
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oldValue := atomic.LoadUint64(&ds.vCPUs[index])
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if oldValue&bit != 0 {
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return false // Not clean.
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}
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// Set the bit unilaterally, and ensure that a flush takes place. Note
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// that it's possible for races to occur here, but since the flush is
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// taking place long after these lines there's no race in practice.
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atomicbitops.OrUint64(&ds.vCPUs[index], bit)
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return true // Previously clean.
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}
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// addressSpace is a wrapper for PageTables.
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type addressSpace struct {
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platform.NoAddressSpaceIO
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// mu is the lock for modifications to the address space.
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//
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// Note that the page tables themselves are not locked.
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mu sync.Mutex
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// filemem is the memory instance.
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filemem *filemem.FileMem
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// machine is the underlying machine.
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machine *machine
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// pageTables are for this particular address space.
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pageTables *pagetables.PageTables
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// dirtySet is the set of dirty vCPUs.
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dirtySet dirtySet
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// files contains files mapped in the host address space.
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//
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// See host_map.go for more information.
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files hostMap
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}
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// invalidate is the implementation for Invalidate.
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func (as *addressSpace) invalidate() {
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as.dirtySet.forEach(as.machine, func(c *vCPU) {
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if c.active.get() == as { // If this happens to be active,
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c.BounceToKernel() // ... force a kernel transition.
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}
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})
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}
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// Invalidate interrupts all dirty contexts.
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func (as *addressSpace) Invalidate() {
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as.mu.Lock()
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defer as.mu.Unlock()
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as.invalidate()
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}
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// Touch adds the given vCPU to the dirty list.
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//
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// The return value indicates whether a flush is required.
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func (as *addressSpace) Touch(c *vCPU) bool {
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return as.dirtySet.mark(c)
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}
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func (as *addressSpace) mapHost(addr usermem.Addr, m hostMapEntry, at usermem.AccessType) (inv bool) {
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for m.length > 0 {
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physical, length, ok := translateToPhysical(m.addr)
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if !ok {
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panic("unable to translate segment")
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}
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if length > m.length {
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length = m.length
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}
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// Ensure that this map has physical mappings. If the page does
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// not have physical mappings, the KVM module may inject
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// spurious exceptions when emulation fails (i.e. it tries to
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// emulate because the RIP is pointed at those pages).
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as.machine.mapPhysical(physical, length)
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// Install the page table mappings. Note that the ordering is
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// important; if the pagetable mappings were installed before
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// ensuring the physical pages were available, then some other
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// thread could theoretically access them.
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//
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// Due to the way KVM's shadow paging implementation works,
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// modifications to the page tables while in host mode may not
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// be trapped, leading to the shadow pages being out of sync.
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// Therefore, we need to ensure that we are in guest mode for
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// page table modifications. See the call to bluepill, below.
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as.machine.retryInGuest(func() {
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inv = as.pageTables.Map(addr, length, pagetables.MapOpts{
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AccessType: at,
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User: true,
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}, physical) || inv
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})
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m.addr += length
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m.length -= length
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addr += usermem.Addr(length)
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}
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return inv
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}
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func (as *addressSpace) mapHostFile(addr usermem.Addr, fd int, fr platform.FileRange, at usermem.AccessType) error {
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// Create custom host mappings.
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ms, err := as.files.CreateMappings(usermem.AddrRange{
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Start: addr,
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End: addr + usermem.Addr(fr.End-fr.Start),
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}, at, fd, fr.Start)
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if err != nil {
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return err
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}
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inv := false
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for _, m := range ms {
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// The host mapped slices are guaranteed to be aligned.
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prev := as.mapHost(addr, m, at)
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inv = inv || prev
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addr += usermem.Addr(m.length)
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}
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if inv {
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as.invalidate()
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}
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return nil
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}
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func (as *addressSpace) mapFilemem(addr usermem.Addr, fr platform.FileRange, at usermem.AccessType, precommit bool) error {
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// TODO: Lock order at the platform level is not sufficiently
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// well-defined to guarantee that the caller (FileMem.MapInto) is not
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// holding any locks that FileMem.MapInternal may take.
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// Retrieve mappings for the underlying filemem. Note that the
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// permissions here are largely irrelevant, since it corresponds to
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// physical memory for the guest. We enforce the given access type
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// below, in the guest page tables.
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bs, err := as.filemem.MapInternal(fr, usermem.AccessType{
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Read: true,
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Write: true,
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})
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if err != nil {
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return err
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}
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// Save the original range for invalidation.
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orig := usermem.AddrRange{
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Start: addr,
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End: addr + usermem.Addr(fr.End-fr.Start),
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}
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inv := false
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for !bs.IsEmpty() {
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b := bs.Head()
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bs = bs.Tail()
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// Since fr was page-aligned, b should also be page-aligned. We do the
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// lookup in our host page tables for this translation.
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s := b.ToSlice()
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if precommit {
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for i := 0; i < len(s); i += usermem.PageSize {
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_ = s[i] // Touch to commit.
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}
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}
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prev := as.mapHost(addr, hostMapEntry{
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addr: reflect.ValueOf(&s[0]).Pointer(),
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length: uintptr(len(s)),
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}, at)
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inv = inv || prev
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addr += usermem.Addr(len(s))
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}
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if inv {
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as.invalidate()
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as.files.DeleteMapping(orig)
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}
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return nil
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}
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// MapFile implements platform.AddressSpace.MapFile.
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func (as *addressSpace) MapFile(addr usermem.Addr, fd int, fr platform.FileRange, at usermem.AccessType, precommit bool) error {
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as.mu.Lock()
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defer as.mu.Unlock()
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// Create an appropriate mapping. If this is filemem, we don't create
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// custom mappings for each in-application mapping. For files however,
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// we create distinct mappings for each address space. Unfortunately,
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// there's not a better way to manage this here. The file underlying
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// this fd can change at any time, so we can't actually index the file
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// and share between address space. Oh well. It's all referring to the
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// same physical pages, hopefully we don't run out of address space.
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if fd != int(as.filemem.File().Fd()) {
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// N.B. precommit is ignored for host files.
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return as.mapHostFile(addr, fd, fr, at)
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}
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return as.mapFilemem(addr, fr, at, precommit)
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}
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// Unmap unmaps the given range by calling pagetables.PageTables.Unmap.
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func (as *addressSpace) Unmap(addr usermem.Addr, length uint64) {
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as.mu.Lock()
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defer as.mu.Unlock()
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// See above re: retryInGuest.
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var prev bool
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as.machine.retryInGuest(func() {
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prev = as.pageTables.Unmap(addr, uintptr(length)) || prev
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})
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if prev {
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as.invalidate()
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as.files.DeleteMapping(usermem.AddrRange{
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Start: addr,
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End: addr + usermem.Addr(length),
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})
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// Recycle any freed intermediate pages.
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as.pageTables.Allocator.Recycle()
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}
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}
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// Release releases the page tables.
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func (as *addressSpace) Release() {
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as.Unmap(0, ^uint64(0))
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// Free all pages from the allocator.
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as.pageTables.Allocator.(allocator).base.Drain()
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// Drop all cached machine references.
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as.machine.dropPageTables(as.pageTables)
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}
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