wvoec3: add membarriers to complete cache flush am: cbfc3c7193

Original change: https://googleplex-android-review.googlesource.com/c/platform/vendor/widevine/+/13719187

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I6f57d5bacfef47e2ebed665cb540e29a1fd44fe6

libwvdrmengine/level3/include/clear_cache_function.h

@@ -1,13 +1,65 @@
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 
-#if __mips__
+#include <linux/membarrier.h>
 #include <sys/syscall.h>
-#include <asm/cachectl.h>
+#include <sys/utsname.h>
+
+#if __mips__
+#  include <asm/cachectl.h>
 #endif
 
+#include "log.h"
+
 namespace wvoec3 {
 
+bool supports_membarier_syscall() {
+  // Check kernel version supports membarrier(2); version 4.16 is required.
+  static constexpr int kRequiredMajor = 4;
+  static constexpr int kRequiredMinor = 16;
+  struct utsname uts;
+  int major = 0, minor = 0;
+  if (uname(&uts) != 0 || strcmp(uts.sysname, "Linux") != 0 ||
+      sscanf(uts.release, "%d.%d", &major, &minor) != 2) {
+    LOGE("Failed to get kernel version");
+    return false;
+  }
+  if (major < kRequiredMajor ||
+      (major == kRequiredMajor && minor < kRequiredMinor)) {
+    LOGE("Kernel version %d, %d < required %d, %d", major, minor,
+         kRequiredMajor, kRequiredMinor);
+    return false;
+  }
+  return true;
+}
+
+#if defined(__NR_membarrier)
+
+// membarrier function is used to complete flush of CPU instruction pipelines.
+// Reference:
+// * membarrier(2)
+// * art::jit::JitMemoryRegion::CommitCode
+int membarrier_function(int command) {
+  static bool supports_membarier = supports_membarier_syscall();
+  if (supports_membarier) {
+    return syscall(__NR_membarrier, command, 0);
+  }
+  errno = ENOSYS;
+  return -1;
+}
+
+#else  // __NR_membarrier
+#  pragma message \
+      "(info): __NR_membarrier unavailable; membarrier_function will be no-op."
+
+int membarrier_function(int) {
+  errno = ENOSYS;
+  return -1;
+}
+
+#endif  // __NR_membarrier
+
 // The Cache Flush function is very processor dependent, and is used by the
 // Level3 code using platform-specific flags.
 // Linked in separately from the rest of the build, since this code isn't
@@ -58,6 +110,12 @@ void clear_cache_function(void *page, size_t len) {
   // TODO(fredgc): silence warning about unused variables.
 #endif
 #endif
+
+#if defined(__arm__) || defined(__aarch64__)
+#  pragma message "(info): inserting membarrier_function calls."
+  membarrier_function(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE);
+  membarrier_function(MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE);
+#endif  // defined(__arm__) || defined(__aarch64__)
 }
 
 }  // namespace wvoec3