Make cacheRemoteRevalidating detect changes to file size

When file size changes outside the sandbox, page cache was not
refreshing file size which is required for cacheRemoteRevalidating.
In fact, cacheRemoteRevalidating should be skipping the cache
completely since it's not really benefiting from it. The cache is
cache is already bypassed for unstable attributes (see
cachePolicy.cacheUAttrs). And althought the cache is called to
map pages, they will always miss the cache and map directly from
the host.

Created a HostMappable struct that maps directly to the host and
use it for files with cacheRemoteRevalidating.

Closes #124

PiperOrigin-RevId: 230998440
Change-Id: Ic5f632eabe33b47241e05e98c95e9b2090ae08fc

3 files changed, 160 insertions, 0 deletions

diff --git a/pkg/sentry/fs/fsutil/BUILD b/pkg/sentry/fs/fsutil/BUILD
index 4965e1a5f..d4767642b 100644
--- a/pkg/sentry/fs/fsutil/BUILD
+++ b/pkg/sentry/fs/fsutil/BUILD
@@ -70,6 +70,8 @@ go_library(
         "host_file_mapper.go",
         "host_file_mapper_state.go",
         "host_file_mapper_unsafe.go",
+        "host_mappable.go",
+        "host_mappable_state.go",
         "inode.go",
         "inode_cached.go",
     ],
diff --git a/pkg/sentry/fs/fsutil/host_mappable.go b/pkg/sentry/fs/fsutil/host_mappable.go
new file mode 100644
index 000000000..4e4bcf4a4
--- /dev/null
+++ b/pkg/sentry/fs/fsutil/host_mappable.go
@@ -0,0 +1,136 @@
+// Copyright 2019 Google LLC
+//
+// 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 fsutil
+
+import (
+	"sync"
+
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/memmap"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/safemem"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+)
+
+// HostMappable implements memmap.Mappable and platform.File over an arbitrary
+// host file descriptor.
+//
+// +stateify savable
+type HostMappable struct {
+	hostFileMapper *HostFileMapper
+
+	mu sync.Mutex `state:"nosave"`
+
+	// fd is the file descriptor to the host. Protected by mu.
+	fd int `state:"nosave"`
+
+	// mappings tracks mappings of the cached file object into
+	// memmap.MappingSpaces so it can invalidated upon save. Protected by mu.
+	mappings memmap.MappingSet
+}
+
+// NewHostMappable creates a new mappable that maps directly to host FD.
+func NewHostMappable() *HostMappable {
+	return &HostMappable{
+		hostFileMapper: NewHostFileMapper(),
+		fd:             -1,
+	}
+}
+
+func (h *HostMappable) getFD() int {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	if h.fd < 0 {
+		panic("HostMappable FD isn't set")
+	}
+	return h.fd
+}
+
+// UpdateFD sets the host FD iff FD hasn't been set before or if there are
+// no mappings.
+func (h *HostMappable) UpdateFD(fd int) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	h.fd = fd
+}
+
+// AddMapping implements memmap.Mappable.AddMapping.
+func (h *HostMappable) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) error {
+	// Hot path. Avoid defers.
+	h.mu.Lock()
+	mapped := h.mappings.AddMapping(ms, ar, offset, writable)
+	for _, r := range mapped {
+		h.hostFileMapper.IncRefOn(r)
+	}
+	h.mu.Unlock()
+	return nil
+}
+
+// RemoveMapping implements memmap.Mappable.RemoveMapping.
+func (h *HostMappable) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) {
+	// Hot path. Avoid defers.
+	h.mu.Lock()
+	unmapped := h.mappings.RemoveMapping(ms, ar, offset, writable)
+	for _, r := range unmapped {
+		h.hostFileMapper.DecRefOn(r)
+	}
+	h.mu.Unlock()
+}
+
+// CopyMapping implements memmap.Mappable.CopyMapping.
+func (h *HostMappable) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64, writable bool) error {
+	return h.AddMapping(ctx, ms, dstAR, offset, writable)
+}
+
+// Translate implements memmap.Mappable.Translate.
+func (h *HostMappable) Translate(ctx context.Context, required, optional memmap.MappableRange, at usermem.AccessType) ([]memmap.Translation, error) {
+	return []memmap.Translation{
+		{
+			Source: optional,
+			File:   h,
+			Offset: optional.Start,
+		},
+	}, nil
+}
+
+// InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.
+func (h *HostMappable) InvalidateUnsavable(ctx context.Context) error {
+	h.mu.Lock()
+	h.mappings.InvalidateAll(memmap.InvalidateOpts{})
+	h.mu.Unlock()
+	return nil
+}
+
+// MapInto implements platform.File.MapInto.
+func (h *HostMappable) MapInto(as platform.AddressSpace, addr usermem.Addr, fr platform.FileRange, at usermem.AccessType, precommit bool) error {
+	return as.MapFile(addr, h.getFD(), fr, at, precommit)
+}
+
+// MapInternal implements platform.File.MapInternal.
+func (h *HostMappable) MapInternal(fr platform.FileRange, at usermem.AccessType) (safemem.BlockSeq, error) {
+	return h.hostFileMapper.MapInternal(fr, h.getFD(), at.Write)
+}
+
+// IncRef implements platform.File.IncRef.
+func (h *HostMappable) IncRef(fr platform.FileRange) {
+	mr := memmap.MappableRange{Start: fr.Start, End: fr.End}
+	h.hostFileMapper.IncRefOn(mr)
+}
+
+// DecRef implements platform.File.DecRef.
+func (h *HostMappable) DecRef(fr platform.FileRange) {
+	mr := memmap.MappableRange{Start: fr.Start, End: fr.End}
+	h.hostFileMapper.DecRefOn(mr)
+}
diff --git a/pkg/sentry/fs/fsutil/host_mappable_state.go b/pkg/sentry/fs/fsutil/host_mappable_state.go
new file mode 100644
index 000000000..765f1ec87
--- /dev/null
+++ b/pkg/sentry/fs/fsutil/host_mappable_state.go
@@ -0,0 +1,22 @@
+// Copyright 2019 Google LLC
+//
+// 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 fsutil
+
+// afterLoad is invoked by stateify.
+func (h *HostMappable) afterLoad() {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	h.fd = -1
+}