[PATCH v2] hmm-tests: Fix migrate_dirty_page test

[Alistair Popple <apopple@nvidia.com>]

As noted by John Hubbard the original test relied on side effects of the
implementation of migrate_vma_setup() to detect if pages had been
swapped to disk or not. This is subject to change in future so
explicitly check for swap entries via pagemap instead. Fix a spelling
mistake while we're at it.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
Fixes: 5cc88e844e87 ("selftests/hmm-tests: add test for dirty bits")
Reviewed-by: Mika Penttilä <mpenttil@redhat.com>

---

Changes for v2:

 - Added Mika's Reviewed-by (Thanks!)
 - Moved pagemap checks into vm_util.c as suggested by David H.
---
 tools/testing/selftests/vm/Makefile    |  1 +
 tools/testing/selftests/vm/hmm-tests.c | 28 ++++++++++++++++++++++----
 tools/testing/selftests/vm/vm_util.c   | 22 ++++++++++++++++++++
 tools/testing/selftests/vm/vm_util.h   |  2 ++
 4 files changed, 49 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
index d9fa6a9ea584..17e36129efd2 100644
--- a/tools/testing/selftests/vm/Makefile
+++ b/tools/testing/selftests/vm/Makefile
@@ -100,6 +100,7 @@ include ../lib.mk
 $(OUTPUT)/madv_populate: vm_util.c
 $(OUTPUT)/soft-dirty: vm_util.c
 $(OUTPUT)/split_huge_page_test: vm_util.c
+$(OUTPUT)/hmm-tests: vm_util.c
 
 ifeq ($(MACHINE),x86_64)
 BINARIES_32 := $(patsubst %,$(OUTPUT)/%,$(BINARIES_32))
diff --git a/tools/testing/selftests/vm/hmm-tests.c b/tools/testing/selftests/vm/hmm-tests.c
index 70fdb49b59ed..509fe8c5158e 100644
--- a/tools/testing/selftests/vm/hmm-tests.c
+++ b/tools/testing/selftests/vm/hmm-tests.c
@@ -37,6 +37,7 @@
  */
 #include "../../../../lib/test_hmm_uapi.h"
 #include "../../../../mm/gup_test.h"
+#include "vm_util.h"
 
 struct hmm_buffer {
 	void		*ptr;
@@ -1261,9 +1262,24 @@ static int destroy_cgroup(void)
 	return 0;
 }
 
+/* Returns true if at least one page in the range is on swap */
+static bool pages_swapped(void *ptr, size_t size)
+{
+	int fd = open("/proc/self/pagemap", O_RDONLY);
+	bool ret;
+
+	if (fd < 0)
+		return false;
+
+	ret = pagemap_range_some_swapped(fd, ptr, size);
+	close(fd);
+
+	return ret;
+}
+
 /*
  * Try and migrate a dirty page that has previously been swapped to disk. This
- * checks that we don't loose dirty bits.
+ * checks that we don't lose dirty bits.
  */
 TEST_F(hmm, migrate_dirty_page)
 {
@@ -1300,6 +1316,10 @@ TEST_F(hmm, migrate_dirty_page)
 
 	ASSERT_FALSE(write_cgroup_param(cgroup, "memory.reclaim", 1UL<<30));
 
+	/* Make sure at least some pages got paged to disk. */
+	if (!pages_swapped(buffer->ptr, size))
+		SKIP(return, "Pages weren't swapped when they should have been");
+
 	/* Fault pages back in from swap as clean pages */
 	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
 		tmp += ptr[i];
@@ -1309,10 +1329,10 @@ TEST_F(hmm, migrate_dirty_page)
 		ptr[i] = i;
 
 	/*
-	 * Attempt to migrate memory to device, which should fail because
-	 * hopefully some pages are backed by swap storage.
+	 * Attempt to migrate memory to device. This might fail if some pages
+	 * are/were backed by swap but that's ok.
 	 */
-	ASSERT_TRUE(hmm_migrate_sys_to_dev(self->fd, buffer, npages));
+	hmm_migrate_sys_to_dev(self->fd, buffer, npages);
 
 	ASSERT_FALSE(write_cgroup_param(cgroup, "memory.reclaim", 1UL<<30));
 
diff --git a/tools/testing/selftests/vm/vm_util.c b/tools/testing/selftests/vm/vm_util.c
index b58ab11a7a30..2768d4f3de4c 100644
--- a/tools/testing/selftests/vm/vm_util.c
+++ b/tools/testing/selftests/vm/vm_util.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <unistd.h>
 #include <string.h>
 #include <fcntl.h>
 #include "../kselftest.h"
@@ -20,6 +21,14 @@ uint64_t pagemap_get_entry(int fd, char *start)
 	return entry;
 }
 
+bool pagemap_is_swapped(int fd, char *start)
+{
+	uint64_t entry = pagemap_get_entry(fd, start);
+
+	// Check if swap entry bit (62nd bit) is set
+	return entry & 0x4000000000000000ull;
+}
+
 bool pagemap_is_softdirty(int fd, char *start)
 {
 	uint64_t entry = pagemap_get_entry(fd, start);
@@ -28,6 +37,19 @@ bool pagemap_is_softdirty(int fd, char *start)
 	return entry & 0x0080000000000000ull;
 }
 
+/* Returns true if at least one page in the range is in swap */
+bool pagemap_range_some_swapped(int fd, char *start, size_t len)
+{
+	unsigned long i;
+	unsigned long npages = len / getpagesize();
+
+	for (i = 0; i < npages; i++)
+		if (pagemap_is_swapped(fd, start + i * getpagesize()))
+			return true;
+
+	return false;
+}
+
 void clear_softdirty(void)
 {
 	int ret;
diff --git a/tools/testing/selftests/vm/vm_util.h b/tools/testing/selftests/vm/vm_util.h
index 2e512bd57ae1..307e11f72341 100644
--- a/tools/testing/selftests/vm/vm_util.h
+++ b/tools/testing/selftests/vm/vm_util.h
@@ -4,6 +4,8 @@
 
 uint64_t pagemap_get_entry(int fd, char *start);
 bool pagemap_is_softdirty(int fd, char *start);
+bool pagemap_is_swapped(int fd, char *start);
+bool pagemap_range_some_swapped(int fd, char *start, size_t len);
 void clear_softdirty(void);
 uint64_t read_pmd_pagesize(void);
 uint64_t check_huge(void *addr);
-- 
2.35.1