[PATCH v5 14/14] KVM: arm64: selftests: arch_timer: Support vCPU migration

Raghavendra Rao Ananta
2021-09-13T20:51:43Z

Since the timer stack (hardware and KVM) is per-CPU, there
are potential chances for races to occur when the scheduler
decides to migrate a vCPU thread to a different physical CPU.
Hence, include an option to stress-test this part as well by
forcing the vCPUs to migrate across physical CPUs in the
system at a particular rate.

Originally, the bug for the fix with commit 3134cc8beb69d0d
("KVM: arm64: vgic: Resample HW pending state on deactivation")
was discovered using arch_timer test with vCPU migrations and
can be easily reproduced.

Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
---
.../selftests/kvm/aarch64/arch_timer.c | 115 +++++++++++++++++-
1 file changed, 114 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/aarch64/arch_timer.c b/tools/testing/selftests/kvm/aarch64/arch_timer.c
index 3b6ea6a462f4..228e7ed5531c 100644
--- a/tools/testing/selftests/kvm/aarch64/arch_timer.c
+++ b/tools/testing/selftests/kvm/aarch64/arch_timer.c
@@ -14,6 +14,8 @@
*
* The test provides command-line options to configure the timer's
* period (-p), number of vCPUs (-n), and iterations per stage (-i).
+ * To stress-test the timer stack even more, an option to migrate the
+ * vCPUs across pCPUs (-m), at a particular rate, is also provided.
*
* Copyright (c) 2021, Google LLC.
*/
@@ -24,6 +26,8 @@
#include <pthread.h>
#include <linux/kvm.h>
#include <linux/sizes.h>
+#include <linux/bitmap.h>
+#include <sys/sysinfo.h>

#include "kvm_util.h"
#include "processor.h"
@@ -36,17 +40,20 @@
#define NR_TEST_ITERS_DEF 5
#define TIMER_TEST_PERIOD_MS_DEF 10
#define TIMER_TEST_ERR_MARGIN_US 100
+#define TIMER_TEST_MIGRATION_FREQ_MS 2

struct test_args {
int nr_vcpus;
int nr_iter;
int timer_period_ms;
+ int migration_freq_ms;
};

static struct test_args test_args = {
.nr_vcpus = NR_VCPUS_DEF,
.nr_iter = NR_TEST_ITERS_DEF,
.timer_period_ms = TIMER_TEST_PERIOD_MS_DEF,
+ .migration_freq_ms = TIMER_TEST_MIGRATION_FREQ_MS,
};

#define msecs_to_usecs(msec) ((msec) * 1000LL)
@@ -80,6 +87,9 @@ static struct test_vcpu_shared_data vcpu_shared_data[KVM_MAX_VCPUS];

static int vtimer_irq, ptimer_irq;

+static unsigned long *vcpu_done_map;
+static pthread_mutex_t vcpu_done_map_lock;
+
static void
guest_configure_timer_action(struct test_vcpu_shared_data *shared_data)
{
@@ -215,6 +225,11 @@ static void *test_vcpu_run(void *arg)

vcpu_run(vm, vcpuid);

+ /* Currently, any exit from guest is an indication of completion */
+ pthread_mutex_lock(&vcpu_done_map_lock);
+ set_bit(vcpuid, vcpu_done_map);
+ pthread_mutex_unlock(&vcpu_done_map_lock);
+
switch (get_ucall(vm, vcpuid, &uc)) {
case UCALL_SYNC:
case UCALL_DONE:
@@ -233,9 +248,78 @@ static void *test_vcpu_run(void *arg)
return NULL;
}

+static uint32_t test_get_pcpu(void)
+{
+ uint32_t pcpu;
+ unsigned int nproc_conf;
+ cpu_set_t online_cpuset;
+
+ nproc_conf = get_nprocs_conf();
+ sched_getaffinity(0, sizeof(cpu_set_t), &online_cpuset);
+
+ /* Randomly find an available pCPU to place a vCPU on */
+ do {
+ pcpu = rand() % nproc_conf;
+ } while (!CPU_ISSET(pcpu, &online_cpuset));
+
+ return pcpu;
+}
+
+static int test_migrate_vcpu(struct test_vcpu *vcpu)
+{
+ int ret;
+ cpu_set_t cpuset;
+ uint32_t new_pcpu = test_get_pcpu();
+
+ CPU_ZERO(&cpuset);
+ CPU_SET(new_pcpu, &cpuset);
+
+ pr_debug("Migrating vCPU: %u to pCPU: %u\n", vcpu->vcpuid, new_pcpu);
+
+ ret = pthread_setaffinity_np(vcpu->pt_vcpu_run,
+ sizeof(cpuset), &cpuset);
+
+ /* Allow the error where the vCPU thread is already finished */
+ TEST_ASSERT(ret == 0 || ret == ESRCH,
+ "Failed to migrate the vCPU:%u to pCPU: %u; ret: %d\n",
+ vcpu->vcpuid, new_pcpu, ret);
+
+ return ret;
+}
+
+static void *test_vcpu_migration(void *arg)
+{
+ unsigned int i, n_done;
+ bool vcpu_done;
+
+ do {
+ usleep(msecs_to_usecs(test_args.migration_freq_ms));
+
+ for (n_done = 0, i = 0; i < test_args.nr_vcpus; i++) {
+ pthread_mutex_lock(&vcpu_done_map_lock);
+ vcpu_done = test_bit(i, vcpu_done_map);
+ pthread_mutex_unlock(&vcpu_done_map_lock);
+
+ if (vcpu_done) {
+ n_done++;
+ continue;
+ }
+
+ test_migrate_vcpu(&test_vcpu[i]);
+ }
+ } while (test_args.nr_vcpus != n_done);
+
+ return NULL;
+}
+
static void test_run(struct kvm_vm *vm)
{
int i, ret;
+ pthread_t pt_vcpu_migration;
+
+ pthread_mutex_init(&vcpu_done_map_lock, NULL);
+ vcpu_done_map = bitmap_alloc(test_args.nr_vcpus);
+ TEST_ASSERT(vcpu_done_map, "Failed to allocate vcpu done bitmap\n");

for (i = 0; i < test_args.nr_vcpus; i++) {
ret = pthread_create(&test_vcpu[i].pt_vcpu_run, NULL,
@@ -243,8 +327,23 @@ static void test_run(struct kvm_vm *vm)
TEST_ASSERT(!ret, "Failed to create vCPU-%d pthread\n", i);
}

+ /* Spawn a thread to control the vCPU migrations */
+ if (test_args.migration_freq_ms) {
+ srand(time(NULL));
+
+ ret = pthread_create(&pt_vcpu_migration, NULL,
+ test_vcpu_migration, NULL);
+ TEST_ASSERT(!ret, "Failed to create the migration pthread\n");
+ }
+
+
for (i = 0; i < test_args.nr_vcpus; i++)
pthread_join(test_vcpu[i].pt_vcpu_run, NULL);
+
+ if (test_args.migration_freq_ms)
+ pthread_join(pt_vcpu_migration, NULL);
+
+ bitmap_free(vcpu_done_map);
}

static void test_init_timer_irq(struct kvm_vm *vm)
@@ -301,6 +400,8 @@ static void test_print_help(char *name)
NR_TEST_ITERS_DEF);
pr_info("\t-p: Periodicity (in ms) of the guest timer (default: %u)\n",
TIMER_TEST_PERIOD_MS_DEF);
+ pr_info("\t-m: Frequency (in ms) of vCPUs to migrate to different pCPU. 0 to turn off (default: %u)\n",
+ TIMER_TEST_MIGRATION_FREQ_MS);
pr_info("\t-h: print this help screen\n");
}

@@ -308,7 +409,7 @@ static bool parse_args(int argc, char *argv[])
{
int opt;

- while ((opt = getopt(argc, argv, "hn:i:p:")) != -1) {
+ while ((opt = getopt(argc, argv, "hn:i:p:m:")) != -1) {
switch (opt) {
case 'n':
test_args.nr_vcpus = atoi(optarg);
@@ -335,6 +436,13 @@ static bool parse_args(int argc, char *argv[])
goto err;
}
break;
+ case 'm':
+ test_args.migration_freq_ms = atoi(optarg);
+ if (test_args.migration_freq_ms < 0) {
+ pr_info("0 or positive value needed for -m\n");
+ goto err;
+ }
+ break;
case 'h':
default:
goto err;
@@ -358,6 +466,11 @@ int main(int argc, char *argv[])
if (!parse_args(argc, argv))
exit(KSFT_SKIP);

+ if (test_args.migration_freq_ms && get_nprocs() < 2) {
+ print_skip("At least two physical CPUs needed for vCPU migration");
+ exit(KSFT_SKIP);
+ }
+
vm = test_vm_create();
test_run(vm);
kvm_vm_free(vm);
--
2.33.0.309.g3052b89438-goog