[vfs] Refactor hostfs mmap into kernfs util.

PiperOrigin-RevId: 339505487

3 files changed, 190 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/BUILD b/pkg/sentry/fsimpl/kernfs/BUILD
index aaad67ab8..6dbc7e34d 100644
--- a/pkg/sentry/fsimpl/kernfs/BUILD
+++ b/pkg/sentry/fsimpl/kernfs/BUILD
@@ -92,6 +92,8 @@ go_library(
         "fstree.go",
         "inode_impl_util.go",
         "kernfs.go",
+        "mmap_util.go",
+        "save_restore.go",
         "slot_list.go",
         "static_directory_refs.go",
         "symlink.go",
@@ -106,6 +108,7 @@ go_library(
         "//pkg/log",
         "//pkg/refs",
         "//pkg/refsvfs2",
+        "//pkg/safemem",
         "//pkg/sentry/fs/fsutil",
         "//pkg/sentry/fs/lock",
         "//pkg/sentry/kernel/auth",
diff --git a/pkg/sentry/fsimpl/kernfs/mmap_util.go b/pkg/sentry/fsimpl/kernfs/mmap_util.go
new file mode 100644
index 000000000..bd6a134b4
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/mmap_util.go
@@ -0,0 +1,164 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package kernfs
+
+import (
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// inodePlatformFile implements memmap.File. It exists solely because inode
+// cannot implement both kernfs.Inode.IncRef and memmap.File.IncRef.
+//
+// +stateify savable
+type inodePlatformFile struct {
+	// hostFD contains the host fd that this file was originally created from,
+	// which must be available at time of restore.
+	//
+	// This field is initialized at creation time and is immutable.
+	// inodePlatformFile does not own hostFD and hence should not close it.
+	hostFD int
+
+	// fdRefsMu protects fdRefs.
+	fdRefsMu sync.Mutex `state:"nosave"`
+
+	// fdRefs counts references on memmap.File offsets. It is used solely for
+	// memory accounting.
+	fdRefs fsutil.FrameRefSet
+
+	// fileMapper caches mappings of the host file represented by this inode.
+	fileMapper fsutil.HostFileMapper
+
+	// fileMapperInitOnce is used to lazily initialize fileMapper.
+	fileMapperInitOnce sync.Once `state:"nosave"`
+}
+
+var _ memmap.File = (*inodePlatformFile)(nil)
+
+// IncRef implements memmap.File.IncRef.
+func (i *inodePlatformFile) IncRef(fr memmap.FileRange) {
+	i.fdRefsMu.Lock()
+	i.fdRefs.IncRefAndAccount(fr)
+	i.fdRefsMu.Unlock()
+}
+
+// DecRef implements memmap.File.DecRef.
+func (i *inodePlatformFile) DecRef(fr memmap.FileRange) {
+	i.fdRefsMu.Lock()
+	i.fdRefs.DecRefAndAccount(fr)
+	i.fdRefsMu.Unlock()
+}
+
+// MapInternal implements memmap.File.MapInternal.
+func (i *inodePlatformFile) MapInternal(fr memmap.FileRange, at usermem.AccessType) (safemem.BlockSeq, error) {
+	return i.fileMapper.MapInternal(fr, i.hostFD, at.Write)
+}
+
+// FD implements memmap.File.FD.
+func (i *inodePlatformFile) FD() int {
+	return i.hostFD
+}
+
+// CachedMappable implements memmap.Mappable. This utility can be embedded in a
+// kernfs.Inode that represents a host file  to make the inode mappable.
+// CachedMappable caches the mappings of the host file. CachedMappable must be
+// initialized (via Init) with a hostFD before use.
+//
+// +stateify savable
+type CachedMappable struct {
+	// mapsMu protects mappings.
+	mapsMu sync.Mutex `state:"nosave"`
+
+	// mappings tracks mappings of hostFD into memmap.MappingSpaces.
+	mappings memmap.MappingSet
+
+	// pf implements memmap.File for mappings backed by a host fd.
+	pf inodePlatformFile
+}
+
+var _ memmap.Mappable = (*CachedMappable)(nil)
+
+// Init initializes i.pf. This must be called before using CachedMappable.
+func (i *CachedMappable) Init(hostFD int) {
+	i.pf.hostFD = hostFD
+}
+
+// AddMapping implements memmap.Mappable.AddMapping.
+func (i *CachedMappable) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) error {
+	i.mapsMu.Lock()
+	mapped := i.mappings.AddMapping(ms, ar, offset, writable)
+	for _, r := range mapped {
+		i.pf.fileMapper.IncRefOn(r)
+	}
+	i.mapsMu.Unlock()
+	return nil
+}
+
+// RemoveMapping implements memmap.Mappable.RemoveMapping.
+func (i *CachedMappable) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) {
+	i.mapsMu.Lock()
+	unmapped := i.mappings.RemoveMapping(ms, ar, offset, writable)
+	for _, r := range unmapped {
+		i.pf.fileMapper.DecRefOn(r)
+	}
+	i.mapsMu.Unlock()
+}
+
+// CopyMapping implements memmap.Mappable.CopyMapping.
+func (i *CachedMappable) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64, writable bool) error {
+	return i.AddMapping(ctx, ms, dstAR, offset, writable)
+}
+
+// Translate implements memmap.Mappable.Translate.
+func (i *CachedMappable) Translate(ctx context.Context, required, optional memmap.MappableRange, at usermem.AccessType) ([]memmap.Translation, error) {
+	mr := optional
+	return []memmap.Translation{
+		{
+			Source: mr,
+			File:   &i.pf,
+			Offset: mr.Start,
+			Perms:  usermem.AnyAccess,
+		},
+	}, nil
+}
+
+// InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.
+func (i *CachedMappable) InvalidateUnsavable(ctx context.Context) error {
+	// We expect the same host fd across save/restore, so all translations
+	// should be valid.
+	return nil
+}
+
+// InvalidateRange invalidates the passed range on i.mappings.
+func (i *CachedMappable) InvalidateRange(r memmap.MappableRange) {
+	i.mapsMu.Lock()
+	i.mappings.Invalidate(r, memmap.InvalidateOpts{
+		// Compare Linux's mm/truncate.c:truncate_setsize() =>
+		// truncate_pagecache() =>
+		// mm/memory.c:unmap_mapping_range(evencows=1).
+		InvalidatePrivate: true,
+	})
+	i.mapsMu.Unlock()
+}
+
+// InitFileMapperOnce initializes the host file mapper. It ensures that the
+// file mapper is initialized just once.
+func (i *CachedMappable) InitFileMapperOnce() {
+	i.pf.fileMapperInitOnce.Do(i.pf.fileMapper.Init)
+}
diff --git a/pkg/sentry/fsimpl/kernfs/save_restore.go b/pkg/sentry/fsimpl/kernfs/save_restore.go
new file mode 100644
index 000000000..1f48de6f1
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/save_restore.go
@@ -0,0 +1,23 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package kernfs
+
+// afterLoad is invoked by stateify.
+func (i *inodePlatformFile) afterLoad() {
+	if i.fileMapper.IsInited() {
+		// Ensure that we don't call i.fileMapper.Init() again.
+		i.fileMapperInitOnce.Do(func() {})
+	}
+}