From 0f1c448ca15485cd7270cf0607acfceacdcefaff Mon Sep 17 00:00:00 2001
From: Stefan Karlsson <stefank@openjdk.org>
Date: Tue, 22 Apr 2025 11:23:40 +0000
Subject: [PATCH] 8354922: ZGC: Use MAP_FIXED_NOREPLACE when reserving memory

Reviewed-by: aboldtch, eosterlund
---
 src/hotspot/os/linux/gc/z/zSyscall_linux.hpp              | 4 ++++
 src/hotspot/os/posix/gc/z/zVirtualMemoryManager_posix.cpp | 7 ++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/hotspot/os/linux/gc/z/zSyscall_linux.hpp b/src/hotspot/os/linux/gc/z/zSyscall_linux.hpp
index 1e1becf5a14..e5978c8d93a 100644
--- a/src/hotspot/os/linux/gc/z/zSyscall_linux.hpp
+++ b/src/hotspot/os/linux/gc/z/zSyscall_linux.hpp
@@ -35,6 +35,10 @@
 #define MPOL_F_ADDR        (1<<1)
 #endif
 
+#ifndef MAP_FIXED_NOREPLACE
+#define MAP_FIXED_NOREPLACE 0x100000
+#endif
+
 class ZSyscall : public AllStatic {
 public:
   static int memfd_create(const char* name, unsigned int flags);
diff --git a/src/hotspot/os/posix/gc/z/zVirtualMemoryManager_posix.cpp b/src/hotspot/os/posix/gc/z/zVirtualMemoryManager_posix.cpp
index 4eea35c8a2e..89bde0557ec 100644
--- a/src/hotspot/os/posix/gc/z/zVirtualMemoryManager_posix.cpp
+++ b/src/hotspot/os/posix/gc/z/zVirtualMemoryManager_posix.cpp
@@ -24,6 +24,9 @@
 #include "gc/z/zAddress.inline.hpp"
 #include "gc/z/zVirtualMemoryManager.hpp"
 #include "logging/log.hpp"
+#ifdef LINUX
+#include "gc/z/zSyscall_linux.hpp"
+#endif
 
 #include <sys/mman.h>
 
@@ -32,7 +35,9 @@ void ZVirtualMemoryReserver::pd_register_callbacks(ZVirtualMemoryRegistry* regis
 }
 
 bool ZVirtualMemoryReserver::pd_reserve(zaddress_unsafe addr, size_t size) {
-  void* const res = mmap((void*)untype(addr), size, PROT_NONE, MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE, -1, 0);
+  const int flags = MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE LINUX_ONLY(|MAP_FIXED_NOREPLACE);
+
+  void* const res = mmap((void*)untype(addr), size, PROT_NONE, flags, -1, 0);
   if (res == MAP_FAILED) {
     // Failed to reserve memory
     return false;