[PATCH v4 2/7] KVM: selftests: access_tracking_perf_test: Add option to skip the sanity check

James Houghton
2025-05-08T18:46:53Z

From: Maxim Levitsky <mlevitsk@redhat.com>

Add an option to skip sanity check of number of still idle pages,
and set it by default to skip, in case hypervisor or NUMA balancing
is detected.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Co-developed-by: James Houghton <jthoughton@google.com>
Signed-off-by: James Houghton <jthoughton@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
---
.../selftests/kvm/access_tracking_perf_test.c | 62 ++++++++++++++++---
.../testing/selftests/kvm/include/test_util.h | 1 +
tools/testing/selftests/kvm/lib/test_util.c | 7 +++
3 files changed, 61 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
index 447e619cf856e..a2ac6fa2ba141 100644
--- a/tools/testing/selftests/kvm/access_tracking_perf_test.c
+++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
@@ -65,6 +65,16 @@ static int vcpu_last_completed_iteration[KVM_MAX_VCPUS];
/* Whether to overlap the regions of memory vCPUs access. */
static bool overlap_memory_access;

+/*
+ * If the test should only warn if there are too many idle pages (i.e., it is
+ * expected).
+ * -1: Not yet set.
+ * 0: We do not expect too many idle pages, so FAIL if too many idle pages.
+ * 1: Having too many idle pages is expected, so merely print a warning if
+ * too many idle pages are found.
+ */
+static int idle_pages_warn_only = -1;
+
struct test_params {
/* The backing source for the region of memory. */
enum vm_mem_backing_src_type backing_src;
@@ -177,18 +187,12 @@ static void mark_vcpu_memory_idle(struct kvm_vm *vm,
* arbitrary; high enough that we ensure most memory access went through
* access tracking but low enough as to not make the test too brittle
* over time and across architectures.
- *
- * When running the guest as a nested VM, "warn" instead of asserting
- * as the TLB size is effectively unlimited and the KVM doesn't
- * explicitly flush the TLB when aging SPTEs. As a result, more pages
- * are cached and the guest won't see the "idle" bit cleared.
*/
if (still_idle >= pages / 10) {
-#ifdef __x86_64__
- TEST_ASSERT(this_cpu_has(X86_FEATURE_HYPERVISOR),
+ TEST_ASSERT(idle_pages_warn_only,
"vCPU%d: Too many pages still idle (%lu out of %lu)",
vcpu_idx, still_idle, pages);
-#endif
+
printf("WARNING: vCPU%d: Too many pages still idle (%lu out of %lu), "
"this will affect performance results.\n",
vcpu_idx, still_idle, pages);
@@ -328,6 +332,32 @@ static void run_test(enum vm_guest_mode mode, void *arg)
memstress_destroy_vm(vm);
}

+static int access_tracking_unreliable(void)
+{
+#ifdef __x86_64__
+ /*
+ * When running nested, the TLB size may be effectively unlimited (for
+ * example, this is the case when running on KVM L0), and KVM doesn't
+ * explicitly flush the TLB when aging SPTEs. As a result, more pages
+ * are cached and the guest won't see the "idle" bit cleared.
+ */
+ if (this_cpu_has(X86_FEATURE_HYPERVISOR)) {
+ puts("Skipping idle page count sanity check, because the test is run nested");
+ return 1;
+ }
+#endif
+ /*
+ * When NUMA balancing is enabled, guest memory will be unmapped to get
+ * NUMA faults, dropping the Accessed bits.
+ */
+ if (is_numa_balancing_enabled()) {
+ puts("Skipping idle page count sanity check, because NUMA balancing is enabled");
+ return 1;
+ }
+
+ return 0;
+}
+
static void help(char *name)
{
puts("");
@@ -342,6 +372,12 @@ static void help(char *name)
printf(" -v: specify the number of vCPUs to run.\n");
printf(" -o: Overlap guest memory accesses instead of partitioning\n"
" them into a separate region of memory for each vCPU.\n");
+ printf(" -w: Control whether the test warns or fails if more than 10%\n"
+ " of pages are still seen as idle/old after accessing guest\n"
+ " memory. >0 == warn only, 0 == fail, <0 == auto. For auto\n"
+ " mode, the test fails by default, but switches to warn only\n"
+ " if NUMA balancing is enabled or the test detects it's running\n"
+ " in a VM.\n");
backing_src_help("-s");
puts("");
exit(0);
@@ -359,7 +395,7 @@ int main(int argc, char *argv[])

guest_modes_append_default();

- while ((opt = getopt(argc, argv, "hm:b:v:os:")) != -1) {
+ while ((opt = getopt(argc, argv, "hm:b:v:os:w:")) != -1) {
switch (opt) {
case 'm':
guest_modes_cmdline(optarg);
@@ -376,6 +412,11 @@ int main(int argc, char *argv[])
case 's':
params.backing_src = parse_backing_src_type(optarg);
break;
+ case 'w':
+ idle_pages_warn_only =
+ atoi_non_negative("Idle pages warning",
+ optarg);
+ break;
case 'h':
default:
help(argv[0]);
@@ -388,6 +429,9 @@ int main(int argc, char *argv[])
"CONFIG_IDLE_PAGE_TRACKING is not enabled");
close(page_idle_fd);

+ if (idle_pages_warn_only == -1)
+ idle_pages_warn_only = access_tracking_unreliable();
+
for_each_guest_mode(run_test, &params);

return 0;
diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
index 77d13d7920cb8..c6ef895fbd9ab 100644
--- a/tools/testing/selftests/kvm/include/test_util.h
+++ b/tools/testing/selftests/kvm/include/test_util.h
@@ -153,6 +153,7 @@ bool is_backing_src_hugetlb(uint32_t i);
void backing_src_help(const char *flag);
enum vm_mem_backing_src_type parse_backing_src_type(const char *type_name);
long get_run_delay(void);
+bool is_numa_balancing_enabled(void);

/*
* Whether or not the given source type is shared memory (as opposed to
diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
index 3dc8538f5d696..03eb99af9b8de 100644
--- a/tools/testing/selftests/kvm/lib/test_util.c
+++ b/tools/testing/selftests/kvm/lib/test_util.c
@@ -176,6 +176,13 @@ size_t get_trans_hugepagesz(void)
return get_sysfs_val("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size");
}

+bool is_numa_balancing_enabled(void)
+{
+ if (!test_sysfs_path("/proc/sys/kernel/numa_balancing"))
+ return false;
+ return get_sysfs_val("/proc/sys/kernel/numa_balancing") == 1;
+}
+
size_t get_def_hugetlb_pagesz(void)
{
char buf[64];
--
2.49.0.1015.ga840276032-goog