--- a/src/hotspot/os_cpu/linux_x86/gc/z/zPhysicalMemoryBacking_linux_x86.cpp	Sun Mar 17 08:26:38 2019 +0000
+++ b/src/hotspot/os_cpu/linux_x86/gc/z/zPhysicalMemoryBacking_linux_x86.cpp	Mon Mar 18 11:50:38 2019 +0100
@@ -237,8 +237,8 @@
 }
 
 void ZPhysicalMemoryBacking::map(ZPhysicalMemory pmem, uintptr_t offset) const {
-  if (ZUnmapBadViews) {
-    // Only map the good view, for debugging only
+  if (ZVerifyViews) {
+    // Map good view
     map_view(pmem, ZAddress::good(offset), AlwaysPreTouch);
   } else {
     // Map all views
@@ -249,8 +249,8 @@
 }
 
 void ZPhysicalMemoryBacking::unmap(ZPhysicalMemory pmem, uintptr_t offset) const {
-  if (ZUnmapBadViews) {
-    // Only map the good view, for debugging only
+  if (ZVerifyViews) {
+    // Unmap good view
     unmap_view(pmem, ZAddress::good(offset));
   } else {
     // Unmap all views
@@ -260,11 +260,14 @@
   }
 }
 
-void ZPhysicalMemoryBacking::flip(ZPhysicalMemory pmem, uintptr_t offset) const {
-  assert(ZUnmapBadViews, "Should be enabled");
-  const uintptr_t addr_good = ZAddress::good(offset);
-  const uintptr_t addr_bad = ZAddress::is_marked(ZAddressGoodMask) ? ZAddress::remapped(offset) : ZAddress::marked(offset);
-  // Map/Unmap views
-  map_view(pmem, addr_good, false /* pretouch */);
-  unmap_view(pmem, addr_bad);
+void ZPhysicalMemoryBacking::debug_map(ZPhysicalMemory pmem, uintptr_t offset) const {
+  // Map good view
+  assert(ZVerifyViews, "Should be enabled");
+  map_view(pmem, ZAddress::good(offset), false /* pretouch */);
 }
+
+void ZPhysicalMemoryBacking::debug_unmap(ZPhysicalMemory pmem, uintptr_t offset) const {
+  // Unmap good view
+  assert(ZVerifyViews, "Should be enabled");
+  unmap_view(pmem, ZAddress::good(offset));
+}

--- a/src/hotspot/os_cpu/linux_x86/gc/z/zPhysicalMemoryBacking_linux_x86.hpp	Sun Mar 17 08:26:38 2019 +0000
+++ b/src/hotspot/os_cpu/linux_x86/gc/z/zPhysicalMemoryBacking_linux_x86.hpp	Mon Mar 18 11:50:38 2019 +0100
@@ -58,7 +58,9 @@
 
   void map(ZPhysicalMemory pmem, uintptr_t offset) const;
   void unmap(ZPhysicalMemory pmem, uintptr_t offset) const;
-  void flip(ZPhysicalMemory pmem, uintptr_t offset) const;
+
+  void debug_map(ZPhysicalMemory pmem, uintptr_t offset) const;
+  void debug_unmap(ZPhysicalMemory pmem, uintptr_t offset) const;
 };
 
 #endif // OS_CPU_LINUX_X86_GC_Z_ZPHYSICALMEMORYBACKING_LINUX_X86_HPP

--- a/src/hotspot/share/gc/z/zHeap.cpp	Sun Mar 17 08:26:38 2019 +0000
+++ b/src/hotspot/share/gc/z/zHeap.cpp	Mon Mar 18 11:50:38 2019 +0100
@@ -247,20 +247,35 @@
   }
 }
 
-void ZHeap::flip_views() {
-  // For debugging only
-  if (ZUnmapBadViews) {
-    // Flip pages
+void ZHeap::before_flip() {
+  if (ZVerifyViews) {
+    // Unmap all pages
+    _page_allocator.unmap_all_pages();
+  }
+}
+
+void ZHeap::after_flip() {
+  if (ZVerifyViews) {
+    // Map all pages
     ZPageTableIterator iter(&_pagetable);
     for (ZPage* page; iter.next(&page);) {
       if (!page->is_detached()) {
-        _page_allocator.flip_page(page);
+        _page_allocator.map_page(page);
       }
     }
+  }
+}
 
-    // Flip pre-mapped memory
-    _page_allocator.flip_pre_mapped();
-  }
+void ZHeap::flip_to_marked() {
+  before_flip();
+  ZAddressMasks::flip_to_marked();
+  after_flip();
+}
+
+void ZHeap::flip_to_remapped() {
+  before_flip();
+  ZAddressMasks::flip_to_remapped();
+  after_flip();
 }
 
 void ZHeap::mark_start() {
@@ -270,8 +285,7 @@
   ZStatSample(ZSamplerHeapUsedBeforeMark, used());
 
   // Flip address view
-  ZAddressMasks::flip_to_marked();
-  flip_views();
+  flip_to_marked();
 
   // Retire allocating pages
   _object_allocator.retire_pages();
@@ -466,8 +480,7 @@
   _unload.finish();
 
   // Flip address view
-  ZAddressMasks::flip_to_remapped();
-  flip_views();
+  flip_to_remapped();
 
   // Enter relocate phase
   ZGlobalPhase = ZPhaseRelocate;

--- a/src/hotspot/share/gc/z/zHeap.hpp	Sun Mar 17 08:26:38 2019 +0000
+++ b/src/hotspot/share/gc/z/zHeap.hpp	Mon Mar 18 11:50:38 2019 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -67,8 +67,13 @@
   size_t heap_max_size() const;
   size_t heap_max_reserve_size() const;
 
+  void before_flip();
+  void after_flip();
+
+  void flip_to_marked();
+  void flip_to_remapped();
+
   void out_of_memory();
-  void flip_views();
   void fixup_partial_loads();
 
 public:

--- a/src/hotspot/share/gc/z/zPageAllocator.cpp	Sun Mar 17 08:26:38 2019 +0000
+++ b/src/hotspot/share/gc/z/zPageAllocator.cpp	Mon Mar 18 11:50:38 2019 +0100
@@ -242,11 +242,6 @@
   _pre_mapped.clear();
 }
 
-void ZPageAllocator::map_page(ZPage* page) {
-  // Map physical memory
-  _physical.map(page->physical_memory(), page->start());
-}
-
 void ZPageAllocator::detach_page(ZPage* page) {
   // Detach the memory mapping.
   detach_memory(page->virtual_memory(), page->physical_memory());
@@ -267,6 +262,21 @@
   delete page;
 }
 
+void ZPageAllocator::map_page(ZPage* page) {
+  // Map physical memory
+  if (!page->is_mapped()) {
+    _physical.map(page->physical_memory(), page->start());
+  } else if (ZVerifyViews) {
+    _physical.debug_map(page->physical_memory(), page->start());
+  }
+}
+
+void ZPageAllocator::unmap_all_pages() {
+  ZPhysicalMemory pmem(ZPhysicalMemorySegment(0 /* start */, ZAddressOffsetMax));
+  _physical.debug_unmap(pmem, 0 /* offset */);
+  pmem.clear();
+}
+
 void ZPageAllocator::flush_detached_pages(ZList<ZPage>* list) {
   ZLocker<ZLock> locker(&_lock);
   list->transfer(&_detached);
@@ -398,9 +408,7 @@
   }
 
   // Map page if needed
-  if (!page->is_mapped()) {
-    map_page(page);
-  }
+  map_page(page);
 
   // Reset page. This updates the page's sequence number and must
   // be done after page allocation, which potentially blocked in
@@ -455,27 +463,6 @@
   pmem.clear();
 }
 
-void ZPageAllocator::flip_page(ZPage* page) {
-  const ZPhysicalMemory& pmem = page->physical_memory();
-  const uintptr_t addr = page->start();
-
-  // Flip physical mapping
-  _physical.flip(pmem, addr);
-}
-
-void ZPageAllocator::flip_pre_mapped() {
-  if (_pre_mapped.available() == 0) {
-    // Nothing to flip
-    return;
-  }
-
-  const ZPhysicalMemory& pmem = _pre_mapped.physical_memory();
-  const ZVirtualMemory& vmem = _pre_mapped.virtual_memory();
-
-  // Flip physical mapping
-  _physical.flip(pmem, vmem.start());
-}
-
 void ZPageAllocator::free_page(ZPage* page, bool reclaimed) {
   ZLocker<ZLock> locker(&_lock);
 

--- a/src/hotspot/share/gc/z/zPageAllocator.hpp	Sun Mar 17 08:26:38 2019 +0000
+++ b/src/hotspot/share/gc/z/zPageAllocator.hpp	Mon Mar 18 11:50:38 2019 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -63,7 +63,6 @@
   size_t try_ensure_unused_for_pre_mapped(size_t size);
 
   ZPage* create_page(uint8_t type, size_t size);
-  void map_page(ZPage* page);
   void detach_page(ZPage* page);
   void flush_pre_mapped();
   void flush_cache(size_t size);
@@ -97,13 +96,13 @@
   void reset_statistics();
 
   ZPage* alloc_page(uint8_t type, size_t size, ZAllocationFlags flags);
-  void flip_page(ZPage* page);
   void free_page(ZPage* page, bool reclaimed);
   void destroy_page(ZPage* page);
 
-  void flush_detached_pages(ZList<ZPage>* list);
+  void map_page(ZPage* page);
+  void unmap_all_pages();
 
-  void flip_pre_mapped();
+  void flush_detached_pages(ZList<ZPage>* list);
 
   bool is_alloc_stalled() const;
   void check_out_of_memory();

--- a/src/hotspot/share/gc/z/zPhysicalMemory.cpp	Sun Mar 17 08:26:38 2019 +0000
+++ b/src/hotspot/share/gc/z/zPhysicalMemory.cpp	Mon Mar 18 11:50:38 2019 +0100
@@ -179,6 +179,10 @@
   _backing.unmap(pmem, offset);
 }
 
-void ZPhysicalMemoryManager::flip(ZPhysicalMemory pmem, uintptr_t offset) {
-  _backing.flip(pmem, offset);
+void ZPhysicalMemoryManager::debug_map(ZPhysicalMemory pmem, uintptr_t offset) {
+  _backing.debug_map(pmem, offset);
 }
+
+void ZPhysicalMemoryManager::debug_unmap(ZPhysicalMemory pmem, uintptr_t offset) {
+  _backing.debug_unmap(pmem, offset);
+}

--- a/src/hotspot/share/gc/z/zPhysicalMemory.hpp	Sun Mar 17 08:26:38 2019 +0000
+++ b/src/hotspot/share/gc/z/zPhysicalMemory.hpp	Mon Mar 18 11:50:38 2019 +0100
@@ -94,7 +94,9 @@
 
   void map(ZPhysicalMemory pmem, uintptr_t offset);
   void unmap(ZPhysicalMemory pmem, uintptr_t offset);
-  void flip(ZPhysicalMemory pmem, uintptr_t offset);
+
+  void debug_map(ZPhysicalMemory pmem, uintptr_t offset);
+  void debug_unmap(ZPhysicalMemory pmem, uintptr_t offset);
 };
 
 #endif // SHARE_GC_Z_ZPHYSICALMEMORY_HPP

--- a/src/hotspot/share/gc/z/z_globals.hpp	Sun Mar 17 08:26:38 2019 +0000
+++ b/src/hotspot/share/gc/z/z_globals.hpp	Mon Mar 18 11:50:38 2019 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -70,8 +70,8 @@
   diagnostic(bool, ZProactive, true,                                        \
           "Enable proactive GC cycles")                                     \
                                                                             \
-  diagnostic(bool, ZUnmapBadViews, false,                                   \
-          "Unmap bad (inactive) heap views")                                \
+  diagnostic(bool, ZVerifyViews, false,                                     \
+          "Verify heap view accesses")                                      \
                                                                             \
   diagnostic(bool, ZVerifyMarking, false,                                   \
           "Verify marking stacks")                                          \

--- a/test/hotspot/jtreg/compiler/gcbarriers/UnsafeIntrinsicsTest.java	Sun Mar 17 08:26:38 2019 +0000
+++ b/test/hotspot/jtreg/compiler/gcbarriers/UnsafeIntrinsicsTest.java	Mon Mar 18 11:50:38 2019 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -27,7 +27,7 @@
  * @modules java.base/jdk.internal.misc:+open
  * @summary Validate barriers after Unsafe getReference, CAS and swap (GetAndSet)
  * @requires vm.gc.Z & !vm.graal.enabled
- * @run main/othervm -XX:+UnlockExperimentalVMOptions -XX:+UseZGC -XX:+UnlockDiagnosticVMOptions -XX:+ZUnmapBadViews -XX:ZCollectionInterval=1 -XX:-CreateCoredumpOnCrash -XX:CompileCommand=dontinline,*::mergeImpl* compiler.gcbarriers.UnsafeIntrinsicsTest
+ * @run main/othervm -XX:+UnlockExperimentalVMOptions -XX:+UseZGC -XX:+UnlockDiagnosticVMOptions -XX:+ZVerifyViews -XX:ZCollectionInterval=1 -XX:-CreateCoredumpOnCrash -XX:CompileCommand=dontinline,*::mergeImpl* compiler.gcbarriers.UnsafeIntrinsicsTest
  */
 
 package compiler.gcbarriers;