Cache pgalloc.MemoryFile in mm.MemoryManager.

This just saves an interface method call and indirection through kernel.Kernel
for a frequently-used resource.

PiperOrigin-RevId: 581318869

pkg/sentry/mm/lifecycle.go

@@ -32,6 +32,7 @@ func NewMemoryManager(p platform.Platform, mfp pgalloc.MemoryFileProvider, sleep
 	return &MemoryManager{
 		p:                  p,
 		mfp:                mfp,
+		mf:                 mfp.MemoryFile(),
 		haveASIO:           p.SupportsAddressSpaceIO(),
 		privateRefs:        &privateRefs{},
 		users:              atomicbitops.FromInt32(1),
@@ -75,6 +76,7 @@ func (mm *MemoryManager) Fork(ctx context.Context) (*MemoryManager, error) {
 	mm2 := &MemoryManager{
 		p:           mm.p,
 		mfp:         mm.mfp,
+		mf:          mm.mf,
 		haveASIO:    mm.haveASIO,
 		layout:      mm.layout,
 		privateRefs: mm.privateRefs,

pkg/sentry/mm/mm.go

@@ -61,6 +61,11 @@ type MemoryManager struct {
 	p   platform.Platform
 	mfp pgalloc.MemoryFileProvider
 
+	// mf is the cached result of mfp.MemoryFile().
+	//
+	// mf is immutable.
+	mf *pgalloc.MemoryFile `state:"nosave"`
+
 	// haveASIO is the cached result of p.SupportsAddressSpaceIO(). Aside from
 	// eliminating an indirect call in the hot I/O path, this makes
 	// MemoryManager.asioEnabled() a leaf function, allowing it to be inlined.

pkg/sentry/mm/pma.go

@@ -215,7 +215,6 @@ func (mm *MemoryManager) getPMAsInternalLocked(ctx context.Context, vseg vmaIter
 	}
 	atomic.StoreUintptr(&vma.lastFault, uintptr(ar.Start))
 
-	mf := mm.mfp.MemoryFile()
 	// Limit the range we allocate to ar, aligned to privateAllocUnit.
 	maskAR := privateAligned(ar)
 	didUnmapAS := false
@@ -241,7 +240,7 @@ func (mm *MemoryManager) getPMAsInternalLocked(ctx context.Context, vseg vmaIter
 				if vma.mappable == nil {
 					// Private anonymous mappings get pmas by allocating.
 					allocAR := optAR.Intersect(maskAR)
-					fr, err := mf.Allocate(uint64(allocAR.Length()), opts)
+					fr, err := mm.mf.Allocate(uint64(allocAR.Length()), opts)
 					if err != nil {
 						return pstart, pgap, err
 					}
@@ -252,9 +251,9 @@ func (mm *MemoryManager) getPMAsInternalLocked(ctx context.Context, vseg vmaIter
 					}
 					mm.addRSSLocked(allocAR)
 					mm.incPrivateRef(fr)
-					mf.IncRef(fr, memCgID)
+					mm.mf.IncRef(fr, memCgID)
 					pseg, pgap = mm.pmas.Insert(pgap, allocAR, pma{
-						file:           mf,
+						file:           mm.mf,
 						off:            fr.Start,
 						translatePerms: hostarch.AnyAccess,
 						effectivePerms: vma.effectivePerms,
@@ -374,7 +373,7 @@ func (mm *MemoryManager) getPMAsInternalLocked(ctx context.Context, vseg vmaIter
 						return pstart, pseg.PrevGap(), err
 					}
 					// Copy contents.
-					fr, err := mf.Allocate(uint64(copyAR.Length()), pgalloc.AllocOpts{
+					fr, err := mm.mf.Allocate(uint64(copyAR.Length()), pgalloc.AllocOpts{
 						Kind:    usage.Anonymous,
 						Mode:    pgalloc.AllocateAndWritePopulate,
 						MemCgID: memCgID,
@@ -410,8 +409,8 @@ func (mm *MemoryManager) getPMAsInternalLocked(ctx context.Context, vseg vmaIter
 					}
 					oldpma.file.DecRef(pseg.fileRange())
 					mm.incPrivateRef(fr)
-					mf.IncRef(fr, memCgID)
-					oldpma.file = mf
+					mm.mf.IncRef(fr, memCgID)
+					oldpma.file = mm.mf
 					oldpma.off = fr.Start
 					oldpma.translatePerms = hostarch.AnyAccess
 					oldpma.effectivePerms = vma.effectivePerms
@@ -975,9 +974,8 @@ func (mm *MemoryManager) decPrivateRef(fr memmap.FileRange) {
 	refSet.MergeAdjacent(fr)
 	mm.privateRefs.mu.Unlock()
 
-	mf := mm.mfp.MemoryFile()
 	for _, fr := range freed {
-		mf.DecRef(fr)
+		mm.mf.DecRef(fr)
 	}
 }
 

pkg/sentry/mm/save_restore.go

@@ -37,9 +37,8 @@ func (mm *MemoryManager) InvalidateUnsavable(ctx context.Context) error {
 
 // beforeSave is invoked by stateify.
 func (mm *MemoryManager) beforeSave() {
-	mf := mm.mfp.MemoryFile()
 	for pseg := mm.pmas.FirstSegment(); pseg.Ok(); pseg = pseg.NextSegment() {
-		if pma := pseg.ValuePtr(); pma.file != mf {
+		if pma := pseg.ValuePtr(); pma.file != mm.mf {
 			// InvalidateUnsavable should have caused all such pmas to be
 			// invalidated.
 			panic(fmt.Sprintf("Can't save pma %#v with non-MemoryFile of type %T:\n%s", pseg.Range(), pma.file, mm))
@@ -49,10 +48,10 @@ func (mm *MemoryManager) beforeSave() {
 
 // afterLoad is invoked by stateify.
 func (mm *MemoryManager) afterLoad() {
+	mm.mf = mm.mfp.MemoryFile()
 	mm.haveASIO = mm.p.SupportsAddressSpaceIO()
-	mf := mm.mfp.MemoryFile()
 	for pseg := mm.pmas.FirstSegment(); pseg.Ok(); pseg = pseg.NextSegment() {
-		pseg.ValuePtr().file = mf
+		pseg.ValuePtr().file = mm.mf
 	}
 }