From 9c950cf06a91e0dfc0eaf8b4aa444683b9850417 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/x/xSyscall_linux.hpp       | 4 ++++
 src/hotspot/os/linux/gc/z/zSyscall_linux.hpp       | 4 ++++
 src/hotspot/os/posix/gc/x/xVirtualMemory_posix.cpp | 7 ++++++-
 src/hotspot/os/posix/gc/z/zVirtualMemory_posix.cpp | 7 ++++++-
 4 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/hotspot/os/linux/gc/x/xSyscall_linux.hpp b/src/hotspot/os/linux/gc/x/xSyscall_linux.hpp
index f16d2b2ffdc..b3be45b49d7 100644
--- a/src/hotspot/os/linux/gc/x/xSyscall_linux.hpp
+++ b/src/hotspot/os/linux/gc/x/xSyscall_linux.hpp
@@ -35,6 +35,10 @@
 #define MPOL_F_ADDR        (1<<1)
 #endif
 
+#ifndef MAP_FIXED_NOREPLACE
+#define MAP_FIXED_NOREPLACE 0x100000
+#endif
+
 class XSyscall : public AllStatic {
 public:
   static int memfd_create(const char* name, unsigned int flags);
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/x/xVirtualMemory_posix.cpp b/src/hotspot/os/posix/gc/x/xVirtualMemory_posix.cpp
index e2422eb0978..2c15c109d6d 100644
--- a/src/hotspot/os/posix/gc/x/xVirtualMemory_posix.cpp
+++ b/src/hotspot/os/posix/gc/x/xVirtualMemory_posix.cpp
@@ -25,6 +25,9 @@
 #include "gc/x/xAddress.inline.hpp"
 #include "gc/x/xVirtualMemory.hpp"
 #include "logging/log.hpp"
+#ifdef LINUX
+#include "gc/x/xSyscall_linux.hpp"
+#endif
 
 #include <sys/mman.h>
 #include <sys/types.h>
@@ -38,7 +41,9 @@ void XVirtualMemoryManager::pd_initialize_after_reserve() {
 }
 
 bool XVirtualMemoryManager::pd_reserve(uintptr_t addr, size_t size) {
-  const uintptr_t res = (uintptr_t)mmap((void*)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);
+
+  const uintptr_t res = (uintptr_t)mmap((void*)addr, size, PROT_NONE, flags, -1, 0);
   if (res == (uintptr_t)MAP_FAILED) {
     // Failed to reserve memory
     return false;
diff --git a/src/hotspot/os/posix/gc/z/zVirtualMemory_posix.cpp b/src/hotspot/os/posix/gc/z/zVirtualMemory_posix.cpp
index 936e734e8ff..dc577bee59f 100644
--- a/src/hotspot/os/posix/gc/z/zVirtualMemory_posix.cpp
+++ b/src/hotspot/os/posix/gc/z/zVirtualMemory_posix.cpp
@@ -25,6 +25,9 @@
 #include "gc/z/zAddress.inline.hpp"
 #include "gc/z/zVirtualMemory.hpp"
 #include "logging/log.hpp"
+#ifdef LINUX
+#include "gc/z/zSyscall_linux.hpp"
+#endif
 
 #include <sys/mman.h>
 #include <sys/types.h>
@@ -38,7 +41,9 @@ void ZVirtualMemoryManager::pd_initialize_after_reserve() {
 }
 
 bool ZVirtualMemoryManager::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;