linux-kernel - [PATCH v2 2/2] selftests/hmm-tests: Add test for dirty bits

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Message-Id: <23069a5c6e07d16d4c4f0951ff003591ffc4f656.1660635033.git-series.apopple@nvidia.com>
Date:   Tue, 16 Aug 2022 17:39:25 +1000
From:   Alistair Popple <apopple@...dia.com>
To:     linux-mm@...ck.org, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org,
        "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        David Hildenbrand <david@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        Karol Herbst <kherbst@...hat.com>,
        Lyude Paul <lyude@...hat.com>, Ben Skeggs <bskeggs@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>, paulus@...abs.org,
        Alistair Popple <apopple@...dia.com>,
        Peter Xu <peterx@...hat.com>, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2 2/2] selftests/hmm-tests: Add test for dirty bits

We were not correctly copying PTE dirty bits to pages during
migrate_vma_setup() calls. This could potentially lead to data loss, so
add a test for this.

Signed-off-by: Alistair Popple <apopple@...dia.com>
---
 tools/testing/selftests/vm/hmm-tests.c | 124 ++++++++++++++++++++++++++-
 1 file changed, 124 insertions(+)

diff --git a/tools/testing/selftests/vm/hmm-tests.c b/tools/testing/selftests/vm/hmm-tests.c
index 529f53b..70fdb49 100644
--- a/tools/testing/selftests/vm/hmm-tests.c
+++ b/tools/testing/selftests/vm/hmm-tests.c
@@ -1200,6 +1200,130 @@ TEST_F(hmm, migrate_multiple)
 	}
 }
 
+static char cgroup[] = "/sys/fs/cgroup/hmm-test-XXXXXX";
+static int write_cgroup_param(char *cgroup_path, char *param, long value)
+{
+	int ret;
+	FILE *f;
+	char *filename;
+
+	if (asprintf(&filename, "%s/%s", cgroup_path, param) < 0)
+		return -1;
+
+	f = fopen(filename, "w");
+	if (!f) {
+		ret = -1;
+		goto out;
+	}
+
+	ret = fprintf(f, "%ld\n", value);
+	if (ret < 0)
+		goto out1;
+
+	ret = 0;
+
+out1:
+	fclose(f);
+out:
+	free(filename);
+
+	return ret;
+}
+
+static int setup_cgroup(void)
+{
+	pid_t pid = getpid();
+	int ret;
+
+	if (!mkdtemp(cgroup))
+		return -1;
+
+	ret = write_cgroup_param(cgroup, "cgroup.procs", pid);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int destroy_cgroup(void)
+{
+	pid_t pid = getpid();
+	int ret;
+
+	ret = write_cgroup_param("/sys/fs/cgroup/cgroup.procs",
+				"cgroup.proc", pid);
+	if (ret)
+		return ret;
+
+	if (rmdir(cgroup))
+		return -1;
+
+	return 0;
+}
+
+/*
+ * Try and migrate a dirty page that has previously been swapped to disk. This
+ * checks that we don't loose dirty bits.
+ */
+TEST_F(hmm, migrate_dirty_page)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int tmp = 0;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	ASSERT_EQ(setup_cgroup(), 0);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Initialize buffer in system memory. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ptr[i] = 0;
+
+	ASSERT_FALSE(write_cgroup_param(cgroup, "memory.reclaim", 1UL<<30));
+
+	/* Fault pages back in from swap as clean pages */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		tmp += ptr[i];
+
+	/* Dirty the pte */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/*
+	 * Attempt to migrate memory to device, which should fail because
+	 * hopefully some pages are backed by swap storage.
+	 */
+	ASSERT_TRUE(hmm_migrate_sys_to_dev(self->fd, buffer, npages));
+
+	ASSERT_FALSE(write_cgroup_param(cgroup, "memory.reclaim", 1UL<<30));
+
+	/* Check we still see the updated data after restoring from swap. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	hmm_buffer_free(buffer);
+	destroy_cgroup();
+}
+
 /*
  * Read anonymous memory multiple times.
  */
-- 
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