[vfs] Refactor hostfs mmap into kernfs util.

PiperOrigin-RevId: 339505487

6 files changed, 86 insertions, 54 deletions

diff --git a/pkg/sentry/fsimpl/host/BUILD b/pkg/sentry/fsimpl/host/BUILD
index dc0f86061..4ae9d6d5e 100644
--- a/pkg/sentry/fsimpl/host/BUILD
+++ b/pkg/sentry/fsimpl/host/BUILD
@@ -33,7 +33,6 @@ go_library(
         "host.go",
         "inode_refs.go",
         "ioctl_unsafe.go",
-        "mmap.go",
         "save_restore.go",
         "socket.go",
         "socket_iovec.go",
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index eeed0f97d..39b902a3e 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -48,6 +48,7 @@ type inode struct {
 	kernfs.InodeNoStatFS
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
+	kernfs.CachedMappable
 	kernfs.InodeTemporary // This holds no meaning as this inode can't be Looked up and is always valid.
 
 	locks vfs.FileLocks
@@ -96,16 +97,6 @@ type inode struct {
 	// Event queue for blocking operations.
 	queue waiter.Queue
 
-	// mapsMu protects mappings.
-	mapsMu sync.Mutex `state:"nosave"`
-
-	// If this file is mmappable, mappings tracks mappings of hostFD into
-	// memmap.MappingSpaces.
-	mappings memmap.MappingSet
-
-	// pf implements platform.File for mappings of hostFD.
-	pf inodePlatformFile
-
 	// If haveBuf is non-zero, hostFD represents a pipe, and buf contains data
 	// read from the pipe from previous calls to inode.beforeSave(). haveBuf
 	// and buf are protected by bufMu. haveBuf is accessed using atomic memory
@@ -135,7 +126,7 @@ func newInode(ctx context.Context, fs *filesystem, hostFD int, savable bool, fil
 		isTTY:    isTTY,
 		savable:  savable,
 	}
-	i.pf.inode = i
+	i.CachedMappable.Init(hostFD)
 	i.EnableLeakCheck()
 
 	// If the hostFD can return EWOULDBLOCK when set to non-blocking, do so and
@@ -439,14 +430,7 @@ func (i *inode) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Cre
 			oldpgend, _ := usermem.PageRoundUp(oldSize)
 			newpgend, _ := usermem.PageRoundUp(s.Size)
 			if oldpgend != newpgend {
-				i.mapsMu.Lock()
-				i.mappings.Invalidate(memmap.MappableRange{newpgend, oldpgend}, 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()
+				i.CachedMappable.InvalidateRange(memmap.MappableRange{newpgend, oldpgend})
 			}
 		}
 	}
@@ -797,7 +781,7 @@ func (f *fileDescription) ConfigureMMap(_ context.Context, opts *memmap.MMapOpts
 		return syserror.ENODEV
 	}
 	i := f.inode
-	i.pf.fileMapperInitOnce.Do(i.pf.fileMapper.Init)
+	i.CachedMappable.InitFileMapperOnce()
 	return vfs.GenericConfigureMMap(&f.vfsfd, i, opts)
 }
 
diff --git a/pkg/sentry/fsimpl/host/save_restore.go b/pkg/sentry/fsimpl/host/save_restore.go
index 7e32a8863..8800652a9 100644
--- a/pkg/sentry/fsimpl/host/save_restore.go
+++ b/pkg/sentry/fsimpl/host/save_restore.go
@@ -68,11 +68,3 @@ func (i *inode) afterLoad() {
 		}
 	}
 }
-
-// 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() {})
-	}
-}
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/host/mmap.go b/pkg/sentry/fsimpl/kernfs/mmap_util.go
index 3d7eb2f96..bd6a134b4 100644
--- a/pkg/sentry/fsimpl/host/mmap.go
+++ b/pkg/sentry/fsimpl/kernfs/mmap_util.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package host
+package kernfs
 
 import (
 	"gvisor.dev/gvisor/pkg/context"
@@ -26,11 +26,14 @@ import (
 // inodePlatformFile implements memmap.File. It exists solely because inode
 // cannot implement both kernfs.Inode.IncRef and memmap.File.IncRef.
 //
-// inodePlatformFile should only be used if inode.canMap is true.
-//
 // +stateify savable
 type inodePlatformFile struct {
-	*inode
+	// 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"`
@@ -46,9 +49,9 @@ type inodePlatformFile struct {
 	fileMapperInitOnce sync.Once `state:"nosave"`
 }
 
+var _ memmap.File = (*inodePlatformFile)(nil)
+
 // IncRef implements memmap.File.IncRef.
-//
-// Precondition: i.inode.canMap must be true.
 func (i *inodePlatformFile) IncRef(fr memmap.FileRange) {
 	i.fdRefsMu.Lock()
 	i.fdRefs.IncRefAndAccount(fr)
@@ -56,8 +59,6 @@ func (i *inodePlatformFile) IncRef(fr memmap.FileRange) {
 }
 
 // DecRef implements memmap.File.DecRef.
-//
-// Precondition: i.inode.canMap must be true.
 func (i *inodePlatformFile) DecRef(fr memmap.FileRange) {
 	i.fdRefsMu.Lock()
 	i.fdRefs.DecRefAndAccount(fr)
@@ -65,8 +66,6 @@ func (i *inodePlatformFile) DecRef(fr memmap.FileRange) {
 }
 
 // MapInternal implements memmap.File.MapInternal.
-//
-// Precondition: i.inode.canMap must be true.
 func (i *inodePlatformFile) MapInternal(fr memmap.FileRange, at usermem.AccessType) (safemem.BlockSeq, error) {
 	return i.fileMapper.MapInternal(fr, i.hostFD, at.Write)
 }
@@ -76,10 +75,32 @@ func (i *inodePlatformFile) FD() int {
 	return i.hostFD
 }
 
-// AddMapping implements memmap.Mappable.AddMapping.
+// 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.
 //
-// Precondition: i.inode.canMap must be true.
-func (i *inode) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) error {
+// +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 {
@@ -90,9 +111,7 @@ func (i *inode) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar userm
 }
 
 // RemoveMapping implements memmap.Mappable.RemoveMapping.
-//
-// Precondition: i.inode.canMap must be true.
-func (i *inode) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) {
+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 {
@@ -102,16 +121,12 @@ func (i *inode) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar us
 }
 
 // CopyMapping implements memmap.Mappable.CopyMapping.
-//
-// Precondition: i.inode.canMap must be true.
-func (i *inode) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64, writable bool) error {
+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.
-//
-// Precondition: i.inode.canMap must be true.
-func (i *inode) Translate(ctx context.Context, required, optional memmap.MappableRange, at usermem.AccessType) ([]memmap.Translation, error) {
+func (i *CachedMappable) Translate(ctx context.Context, required, optional memmap.MappableRange, at usermem.AccessType) ([]memmap.Translation, error) {
 	mr := optional
 	return []memmap.Translation{
 		{
@@ -124,10 +139,26 @@ func (i *inode) Translate(ctx context.Context, required, optional memmap.Mappabl
 }
 
 // InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.
-//
-// Precondition: i.inode.canMap must be true.
-func (i *inode) InvalidateUnsavable(ctx context.Context) error {
+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() {})
+	}
+}