[PATCH v4 4/4] selftests/hmm-tests: Add test for dirty bits

Alistair Popple
2022-09-02T00:36:57Z

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@nvidia.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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