linux-kernel - [PATCH v2 1/3] selftests/mm: virtual_address_range: mmap() without PROT

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Message-Id: <20250110-virtual_address_range-tests-v2-1-262a2bf3c3d0@linutronix.de>
Date: Fri, 10 Jan 2025 14:05:50 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 Shuah Khan <shuah@...nel.org>, Dev Jain <dev.jain@....com>, 
 Thomas Gleixner <tglx@...utronix.de>, David Hildenbrand <david@...hat.com>
Cc: linux-mm@...ck.org, linux-kselftest@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH v2 1/3] selftests/mm: virtual_address_range: mmap() without
 PROT_WRITE

When mapping a larger chunk than physical memory is available with
PROT_WRITE and overcommit is disabled, the mapping will fail.
This will prevent the test from running on systems with less then ~1GiB
of memory and triggering an inscrutinable test failure.
As the mappings are never written to anyways, the flag can be removed.

Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>

---
I went with dropping PROT_WRITE instead of adding MAP_NORESERVE as this
works even in the face of OVERCOMMIT_NEVER.
---
 tools/testing/selftests/mm/virtual_address_range.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c
index 2a2b69e91950a37999f606847c9c8328d79890c2..ea6ccf49ef4c552f26317c2a40b09bca1a677f8f 100644
--- a/tools/testing/selftests/mm/virtual_address_range.c
+++ b/tools/testing/selftests/mm/virtual_address_range.c
@@ -166,7 +166,7 @@ int main(int argc, char *argv[])
 	ksft_set_plan(1);
 
 	for (i = 0; i < NR_CHUNKS_LOW; i++) {
-		ptr[i] = mmap(NULL, MAP_CHUNK_SIZE, PROT_READ | PROT_WRITE,
+		ptr[i] = mmap(NULL, MAP_CHUNK_SIZE, PROT_READ,
 			      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 
 		if (ptr[i] == MAP_FAILED) {
@@ -186,7 +186,7 @@ int main(int argc, char *argv[])
 
 	for (i = 0; i < NR_CHUNKS_HIGH; i++) {
 		hint = hint_addr();
-		hptr[i] = mmap(hint, MAP_CHUNK_SIZE, PROT_READ | PROT_WRITE,
+		hptr[i] = mmap(hint, MAP_CHUNK_SIZE, PROT_READ,
 			       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 
 		if (hptr[i] == MAP_FAILED)

-- 
2.47.1