linux-kernel - [PATCH 2/2] tools/selftests: add guard region test for /proc/$pid/pagemap

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Message-ID: <164feb0a43ae72650e6b20c3910213f469566311.1740139449.git.lorenzo.stoakes@oracle.com>
Date: Fri, 21 Feb 2025 12:05:23 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Matthew Wilcox <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>,
        "Paul E . McKenney" <paulmck@...nel.org>, Jann Horn <jannh@...gle.com>,
        Juan Yescas <jyescas@...gle.com>, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: [PATCH 2/2] tools/selftests: add guard region test for /proc/$pid/pagemap

Add a test to the guard region self tests to assert that the
/proc/$pid/pagemap information now made availabile to the user correctly
identifies and reports guard regions.

As a part of this change, update vm_util.h to add the new bit (note there
is no header file in the kernel where this is exposed, the user is expected
to provide their own mask) and utilise the helper functions there for
pagemap functionality.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 tools/testing/selftests/mm/guard-regions.c | 47 ++++++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h       |  1 +
 2 files changed, 48 insertions(+)

diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c
index ea9b5815e828..0c7183e8b661 100644
--- a/tools/testing/selftests/mm/guard-regions.c
+++ b/tools/testing/selftests/mm/guard-regions.c
@@ -19,6 +19,7 @@
 #include <sys/syscall.h>
 #include <sys/uio.h>
 #include <unistd.h>
+#include "vm_util.h"
 
 /*
  * Ignore the checkpatch warning, as per the C99 standard, section 7.14.1.1:
@@ -2032,4 +2033,50 @@ TEST_F(guard_regions, anon_zeropage)
 	ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
 }
 
+/*
+ * Assert that /proc/$pid/pagemap correctly identifies guard region ranges.
+ */
+TEST_F(guard_regions, pagemap)
+{
+	const unsigned long page_size = self->page_size;
+	int proc_fd;
+	char *ptr;
+	int i;
+
+	proc_fd = open("/proc/self/pagemap", O_RDONLY);
+	ASSERT_NE(proc_fd, -1);
+
+	ptr = mmap_(self, variant, NULL, 10 * page_size,
+		    PROT_READ | PROT_WRITE, 0, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+
+	/* Read from pagemap, and assert no guard regions are detected. */
+	for (i = 0; i < 10; i++) {
+		char *ptr_p = &ptr[i * page_size];
+		unsigned long entry = pagemap_get_entry(proc_fd, ptr_p);
+		unsigned long masked = entry & PM_GUARD_REGION_MASK;
+
+		ASSERT_EQ(masked, 0);
+	}
+
+	/* Install a guard region in every other page. */
+	for (i = 0; i < 10; i += 2) {
+		char *ptr_p = &ptr[i * page_size];
+
+		ASSERT_EQ(madvise(ptr_p, page_size, MADV_GUARD_INSTALL), 0);
+	}
+
+	/* Re-read from pagemap, and assert guard regions are detected. */
+	for (i = 0; i < 10; i++) {
+		char *ptr_p = &ptr[i * page_size];
+		unsigned long entry = pagemap_get_entry(proc_fd, ptr_p);
+		unsigned long masked = entry & PM_GUARD_REGION_MASK;
+
+		ASSERT_EQ(masked, i % 2 == 0 ? PM_GUARD_REGION_MASK : 0);
+	}
+
+	ASSERT_EQ(close(proc_fd), 0);
+	ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
 TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index b60ac68a9dc8..73a11443b7f6 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -10,6 +10,7 @@
 #define PM_SOFT_DIRTY                 BIT_ULL(55)
 #define PM_MMAP_EXCLUSIVE             BIT_ULL(56)
 #define PM_UFFD_WP                    BIT_ULL(57)
+#define PM_GUARD_REGION_MASK          BIT_ULL(58)
 #define PM_FILE                       BIT_ULL(61)
 #define PM_SWAP                       BIT_ULL(62)
 #define PM_PRESENT                    BIT_ULL(63)
-- 
2.48.1