3 files changed, 55 insertions, 0 deletions
diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
index 064e7b125643..da030b43e43b 100644
--- a/tools/testing/selftests/mm/.gitignore
+++ b/tools/testing/selftests/mm/.gitignore
@@ -50,3 +50,4 @@ hugetlb_fault_after_madv
 hugetlb_madv_vs_map
 mseal_test
 seal_elf
+droppable
diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index e1aa09ddaa3d..901e0d07765b 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -76,6 +76,7 @@ TEST_GEN_FILES += mdwe_test
 TEST_GEN_FILES += hugetlb_fault_after_madv
 TEST_GEN_FILES += hugetlb_madv_vs_map
 TEST_GEN_FILES += hugetlb_dio
+TEST_GEN_FILES += droppable
 
 ifneq ($(ARCH),arm64)
 TEST_GEN_FILES += soft-dirty
diff --git a/tools/testing/selftests/mm/droppable.c b/tools/testing/selftests/mm/droppable.c
new file mode 100644
index 000000000000..f3d9ecf96890
--- /dev/null
+++ b/tools/testing/selftests/mm/droppable.c
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <signal.h>
+#include <sys/mman.h>
+#include <linux/mman.h>
+
+#include "../kselftest.h"
+
+int main(int argc, char *argv[])
+{
+	size_t alloc_size = 134217728;
+	size_t page_size = getpagesize();
+	void *alloc;
+	pid_t child;
+
+	ksft_print_header();
+	ksft_set_plan(1);
+
+	alloc = mmap(0, alloc_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_DROPPABLE, -1, 0);
+	assert(alloc != MAP_FAILED);
+	memset(alloc, 'A', alloc_size);
+	for (size_t i = 0; i < alloc_size; i += page_size)
+		assert(*(uint8_t *)(alloc + i));
+
+	child = fork();
+	assert(child >= 0);
+	if (!child) {
+		for (;;)
+			*(char *)malloc(page_size) = 'B';
+	}
+
+	for (bool done = false; !done;) {
+		for (size_t i = 0; i < alloc_size; i += page_size) {
+			if (!*(uint8_t *)(alloc + i)) {
+				done = true;
+				break;
+			}
+		}
+	}
+	kill(child, SIGTERM);
+
+	ksft_test_result_pass("MAP_DROPPABLE: PASS\n");
+	exit(KSFT_PASS);
+}