On Wed, Sep 01, 2021 at 09:14:12PM +0000, Raghavendra Rao Ananta wrote:
> 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@xxxxxxxxxx>
> ---
> .../selftests/kvm/aarch64/arch_timer.c | 108 +++++++++++++++++-
> 1 file changed, 107 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/kvm/aarch64/arch_timer.c b/tools/testing/selftests/kvm/aarch64/arch_timer.c
> index 1383f33850e9..de246c7afab2 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"
> @@ -41,12 +45,14 @@ 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 = 0, /* Turn off migrations by default */
I'd rather we enable good tests like these by default.
> };
>
> #define msecs_to_usecs(msec) ((msec) * 1000LL)
> @@ -81,6 +87,9 @@ struct test_vcpu {
> static struct test_vcpu test_vcpu[KVM_MAX_VCPUS];
> static struct test_vcpu_shared_data vcpu_shared_data[KVM_MAX_VCPUS];
>
> +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)
> {
> @@ -216,6 +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:
> @@ -235,9 +249,73 @@ 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);
> + 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);
It'd be good to collect stats for the two cases so we know how many
vcpus we actually migrated with a successful setaffinity and how many
just completed too early. If our stats don't look good, then we can
adjust our timeouts and frequencies.
> +
> + 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,
> @@ -245,8 +323,23 @@ 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 struct kvm_vm *test_vm_create(void)
> @@ -286,6 +379,7 @@ 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: 0)\n");
> pr_info("\t-h: print this help screen\n");
> }
>
> @@ -293,7 +387,7 @@ 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);
> @@ -320,6 +414,13 @@ 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;
> @@ -343,6 +444,11 @@ int main(int argc, char *argv[])
> if (!parse_args(argc, argv))
> exit(KSFT_SKIP);
>
> + if (get_nprocs() < 2) {
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);
> --
> 2.33.0.153.gba50c8fa24-goog
>
Thanks,
drew
