Use kernel cacheflush for large sizes on MIPS.android-4.3_r3.1android-4.3_r3android-4.3_r2.3android-4.3_r2.2android-4.3_r2.1android-4.3_r2android-4.3_r1.1android-4.3_r1android-4.3_r0.9.1android-4.3_r0.9android-4.3.1_r1jb-mr2.0.0-releasejb-mr2.0-releasejb-mr2-releasejb-mr2-dev

This is a workaround to a deserializer bug. The bug was exposed
with a recent optimization to use user-mode cache-flushing on
MIPS. To reduce risk, we're doing a workaround in mips-specific
code so that other arch's cannot be affected.

The deserializer does this FlushICache:

  CPU::FlushICache(last_object_address_, Page::kPageSize);

However, that region includes OS guard-pages with no access
privilege. The MIPS kernel cacheflush routines work OK in this
case, but the Bionic cacheflush recently enabled user-mode flushing
using the synci instruction, which causes a segfault on MIPS when
the guard pages are reached.
(change I48fd6f2b0cbe80c3cd90f453ced97a2f154f7ad3)

The workaround just reverts to the kernel flush when the size
is Page::kPageSize or bigger.

A better fix would be to alter the deserializer so that only the
executable pages are flushed:
  CPU::FlushICache(last_object_address_,
                   isolate_->memory_allocator()->CodePageAreaSize());

However, that changes common code for all supported architectures.
There is no evidence that this bug affects the other arch's, so we
are doing a MIPS-specific workaround.

(cherry-pick from AOSP)
bug: 8851838

Change-Id: I30b62eb579feab1453d3ae85a5fb9b408f91756b
Signed-off-by: Paul Lind <paul.lind@imgtec.com>

1 files changed, 17 insertions, 4 deletions

diff --git a/src/mips/cpu-mips.cc b/src/mips/cpu-mips.cc
index 93ebeda8..b8200007 100644
--- a/src/mips/cpu-mips.cc
+++ b/src/mips/cpu-mips.cc
@@ -65,10 +65,23 @@ void CPU::FlushICache(void* start, size_t size) {
 
 #if !defined (USE_SIMULATOR)
 #if defined(ANDROID)
-  // Bionic cacheflush can typically run in userland, avoiding kernel call.
-  char *end = reinterpret_cast<char *>(start) + size;
-  cacheflush(
-    reinterpret_cast<intptr_t>(start), reinterpret_cast<intptr_t>(end), 0);
+  // Workaround for a deserializer bug. Bionic usermode cacheflush
+  // fails in deserializer for a size of Page::kPageSize (1MB),
+  // because that region contains protected pages. Switch to kernel
+  // cacheflush in this case.
+  if (size >= static_cast<size_t>(Page::kPageSize)) {
+    int res;
+    // See http://www.linux-mips.org/wiki/Cacheflush_Syscall.
+    res = syscall(__NR_cacheflush, start, size, ICACHE);
+    if (res) {
+      V8_Fatal(__FILE__, __LINE__, "Failed to flush the instruction cache");
+    }
+  } else {
+    // Bionic cacheflush can typically run in userland, avoiding kernel call.
+    char *end = reinterpret_cast<char *>(start) + size;
+    cacheflush(
+      reinterpret_cast<intptr_t>(start), reinterpret_cast<intptr_t>(end), 0);
+  }
 #else  // ANDROID
   int res;
   // See http://www.linux-mips.org/wiki/Cacheflush_Syscall.