Implement membarrier(2) commands other than *_SYNC_CORE.

Updates #267

PiperOrigin-RevId: 335713923

2 files changed, 21 insertions, 0 deletions

diff --git a/pkg/sentry/mm/mm.go b/pkg/sentry/mm/mm.go
index 8c9f11cce..43567b92c 100644
--- a/pkg/sentry/mm/mm.go
+++ b/pkg/sentry/mm/mm.go
@@ -235,6 +235,14 @@ type MemoryManager struct {
 
 	// vdsoSigReturnAddr is the address of 'vdso_sigreturn'.
 	vdsoSigReturnAddr uint64
+
+	// membarrierPrivateEnabled is non-zero if EnableMembarrierPrivate has
+	// previously been called. Since, as of this writing,
+	// MEMBARRIER_CMD_PRIVATE_EXPEDITED is implemented as a global memory
+	// barrier, membarrierPrivateEnabled has no other effect.
+	//
+	// membarrierPrivateEnabled is accessed using atomic memory operations.
+	membarrierPrivateEnabled uint32
 }
 
 // vma represents a virtual memory area.
diff --git a/pkg/sentry/mm/syscalls.go b/pkg/sentry/mm/syscalls.go
index a2555ba1a..0a66b1cdd 100644
--- a/pkg/sentry/mm/syscalls.go
+++ b/pkg/sentry/mm/syscalls.go
@@ -17,6 +17,7 @@ package mm
 import (
 	"fmt"
 	mrand "math/rand"
+	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
@@ -1274,3 +1275,15 @@ func (mm *MemoryManager) VirtualDataSize() uint64 {
 	defer mm.mappingMu.RUnlock()
 	return mm.dataAS
 }
+
+// EnableMembarrierPrivate causes future calls to IsMembarrierPrivateEnabled to
+// return true.
+func (mm *MemoryManager) EnableMembarrierPrivate() {
+	atomic.StoreUint32(&mm.membarrierPrivateEnabled, 1)
+}
+
+// IsMembarrierPrivateEnabled returns true if mm.EnableMembarrierPrivate() has
+// previously been called.
+func (mm *MemoryManager) IsMembarrierPrivateEnabled() bool {
+	return atomic.LoadUint32(&mm.membarrierPrivateEnabled) != 0
+}