Re: [PATCH 2/2] KVM: selftests: Add UFFD_FEATURE_SIGBUS page-in tests

On Wed, May 19, 2021 at 2:04 PM James Houghton jthoughton@google.com wrote:

This exercises the KVM userfaultfd SIGBUS path to perform page-ins. This patch is based on Axel Rasmussen's patches that enable testing with HugeTLBFS: (https://lore.kernel.org/patchwork/patch/1432055/).

This allows me to easily verify that the KVM patch does indeed work for anonymous, shmem-backed, and hugetlbfs-backed pages.

Signed-off-by: James Houghton jthoughton@google.com

.../selftests/kvm/demand_paging_test.c | 193 +++++++++++++-----

If you'd be willing to split this patch up into a few smaller patches, I'd find it much easier to review. Thank you for updating this test with your SIGBUS patch.

1 file changed, 138 insertions(+), 55 deletions(-)

diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c index 60d9b5223b9d..fe5f6fdf4b28 100644 --- a/tools/testing/selftests/kvm/demand_paging_test.c +++ b/tools/testing/selftests/kvm/demand_paging_test.c @@ -10,6 +10,7 @@ #define _GNU_SOURCE /* for pipe2 */

#include <inttypes.h> +#include <stdatomic.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> @@ -17,6 +18,7 @@ #include <poll.h> #include <pthread.h> #include <linux/userfaultfd.h> +#include <signal.h> #include <sys/syscall.h>

#include "kvm_util.h" @@ -43,37 +45,25 @@ static uint64_t guest_percpu_mem_size = DEFAULT_PER_VCPU_MEM_SIZE; static size_t demand_paging_size; static char *guest_data_prototype;

-static void *vcpu_worker(void *data) -{

•   int ret;
  

•   struct perf_test_vcpu_args *vcpu_args = (struct perf_test_vcpu_args *)data;
  

•   int vcpu_id = vcpu_args->vcpu_id;
  

•   struct kvm_vm *vm = perf_test_args.vm;
  

•   struct kvm_run *run;
  

•   struct timespec start;
  

•   struct timespec ts_diff;
  

•   vcpu_args_set(vm, vcpu_id, 1, vcpu_id);
  

•   run = vcpu_state(vm, vcpu_id);
  

•   clock_gettime(CLOCK_MONOTONIC, &start);
  

•   /* Let the guest access its memory */
  

•   ret = _vcpu_run(vm, vcpu_id);
  

•   TEST_ASSERT(ret == 0, "vcpu_run failed: %d\n", ret);
  

•   if (get_ucall(vm, vcpu_id, NULL) != UCALL_SYNC) {
  

•           TEST_ASSERT(false,
  

•                       "Invalid guest sync status: exit_reason=%s\n",
  

•                       exit_reason_str(run->exit_reason));
  

•   }
  

+__thread uint64_t sigbus_address; +__thread atomic_bool sigbus_pending_fault;

•   ts_diff = timespec_elapsed(start);
  

•   PER_VCPU_DEBUG("vCPU %d execution time: %ld.%.9lds\n", vcpu_id,
  

•                  ts_diff.tv_sec, ts_diff.tv_nsec);
  

+static void handle_uffd_sigbus(int signum, siginfo_t *info, void *ctx) +{

•   // Round down address.
  

•   uint64_t mask = ~(demand_paging_size - 1);
  
  

•   return NULL;
  

•   sigbus_address = (unsigned long long)(info->si_addr) & mask;
  

•   atomic_store_explicit(&sigbus_pending_fault, true, memory_order_release);
  

}

+struct vcpu_worker_args {

•   struct perf_test_vcpu_args *vcpu_args;
  

•   int uffd;
  

•   int uffd_mode;
  

•   bool use_uffd_sigbus;
  

+};

static int handle_uffd_page_request(int uffd_mode, int uffd, uint64_t addr) { pid_t tid = syscall(__NR_gettid); @@ -123,6 +113,53 @@ static int handle_uffd_page_request(int uffd_mode, int uffd, uint64_t addr) return 0; }

+static void *vcpu_worker(void *data) +{

•   int ret;
  

•   struct vcpu_worker_args *vcpu_worker_args =
  

•       (struct vcpu_worker_args *)data;
  

•   struct perf_test_vcpu_args *vcpu_args = vcpu_worker_args->vcpu_args;
  

•   int vcpu_id = vcpu_args->vcpu_id;
  

•   struct kvm_vm *vm = perf_test_args.vm;
  

•   struct kvm_run *run;
  

•   struct timespec start;
  

•   struct timespec ts_diff;
  

•   vcpu_args_set(vm, vcpu_id, 1, vcpu_id);
  

•   run = vcpu_state(vm, vcpu_id);
  

•   clock_gettime(CLOCK_MONOTONIC, &start);
  

•   /* Let the guest access its memory */
  

•   for (;;) {
  

•           ret = _vcpu_run(vm, vcpu_id);
  

•           if (vcpu_worker_args->use_uffd_sigbus &&
  

•               atomic_load_explicit(&sigbus_pending_fault,
  

•                                    memory_order_acquire)) {
  

•                   int r = handle_uffd_page_request(
  

•                                   vcpu_worker_args->uffd_mode,
  

•                                   vcpu_worker_args->uffd, sigbus_address);
  

•                   TEST_ASSERT(r == 0, "handle_uffd_page_request failed");
  

•                   atomic_store_explicit(&sigbus_pending_fault, false,
  

•                                         memory_order_relaxed);
  

•           } else
  

•                   break;
  

•   }
  

•   TEST_ASSERT(ret == 0, "vcpu_run failed: %d\n", ret);
  

•   if (get_ucall(vm, vcpu_id, NULL) != UCALL_SYNC) {
  

•           TEST_ASSERT(false,
  

•                       "Invalid guest sync status: exit_reason=%s\n",
  

•                       exit_reason_str(run->exit_reason));
  

•   }
  

•   ts_diff = timespec_elapsed(start);
  

•   PER_VCPU_DEBUG("vCPU %d execution time: %ld.%.9lds\n", vcpu_id,
  

•                  ts_diff.tv_sec, ts_diff.tv_nsec);
  

•   return NULL;
  

+}

bool quit_uffd_thread;

struct uffd_handler_args { @@ -217,11 +254,8 @@ static void *uffd_handler_thread_fn(void *arg) return NULL; }

-static void setup_demand_paging(struct kvm_vm *vm,

•                           pthread_t *uffd_handler_thread, int pipefd,
  

•                           int uffd_mode, useconds_t uffd_delay,
  

•                           struct uffd_handler_args *uffd_args,
  

•                           void *hva, void *alias, uint64_t len)
  

+static int create_userfaultfd(int uffd_mode, bool use_uffd_sigbus,

•                         void *hva, void *alias, uint64_t len)
  

{ bool is_minor = (uffd_mode == UFFDIO_REGISTER_MODE_MINOR); int uffd; @@ -250,7 +284,7 @@ static void setup_demand_paging(struct kvm_vm *vm, TEST_ASSERT(uffd >= 0, "uffd creation failed, errno: %d", errno);

    uffdio_api.api = UFFD_API;

•   uffdio_api.features = 0;
  

•   uffdio_api.features = use_uffd_sigbus ? UFFD_FEATURE_SIGBUS : 0;
    TEST_ASSERT(ioctl(uffd, UFFDIO_API, &uffdio_api) != -1,
                "ioctl UFFDIO_API failed: %" PRIu64,
                (uint64_t)uffdio_api.api);
  

@@ -263,19 +297,29 @@ static void setup_demand_paging(struct kvm_vm *vm, TEST_ASSERT((uffdio_register.ioctls & expected_ioctls) == expected_ioctls, "missing userfaultfd ioctls");

•   return uffd;
  

+}

+static void start_uffd_thread(pthread_t *uffd_handler_thread, int *pipefds,

•                         int uffd, int uffd_mode, useconds_t uffd_delay,
  

•                         struct uffd_handler_args *uffd_args)
  

+{

•   int r;
  

•   r = pipe2(pipefds, O_CLOEXEC | O_NONBLOCK);
  

•   TEST_ASSERT(!r, "Failed to set up pipefd");
  

•   uffd_args->uffd_mode = uffd_mode;
    uffd_args->uffd = uffd;
  

•   uffd_args->pipefd = pipefd;
  

•   uffd_args->pipefd = pipefds[0];
    uffd_args->delay = uffd_delay;
    pthread_create(uffd_handler_thread, NULL, uffd_handler_thread_fn,
                   uffd_args);
  

•   PER_VCPU_DEBUG("Created uffd thread for HVA range [%p, %p)\n",
  

•                  hva, hva + len);
  

}

struct test_params { int uffd_mode;

•   bool use_uffd_sigbus;
    useconds_t uffd_delay;
    enum vm_mem_backing_src_type src_type;
    bool partition_vcpu_memory_access;
  

@@ -286,6 +330,7 @@ static void run_test(enum vm_guest_mode mode, void *arg) struct test_params *p = arg; pthread_t *vcpu_threads; pthread_t *uffd_handler_threads = NULL;

•   struct vcpu_worker_args *vcpu_worker_args = NULL;
    struct uffd_handler_args *uffd_args = NULL;
    struct timespec start;
    struct timespec ts_diff;
  

@@ -293,6 +338,7 @@ static void run_test(enum vm_guest_mode mode, void *arg) struct kvm_vm *vm; int vcpu_id; int r;

•   bool uffd_threads_needed;
  
    vm = perf_test_create_vm(mode, nr_vcpus, guest_percpu_mem_size,
                             p->src_type);
  

@@ -309,10 +355,16 @@ static void run_test(enum vm_guest_mode mode, void *arg) vcpu_threads = malloc(nr_vcpus * sizeof(*vcpu_threads)); TEST_ASSERT(vcpu_threads, "Memory allocation failed");

•   vcpu_worker_args = malloc(nr_vcpus * sizeof(*vcpu_worker_args));
  

•   TEST_ASSERT(vcpu_worker_args, "Memory allocation failed");
  

•   perf_test_setup_vcpus(vm, nr_vcpus, guest_percpu_mem_size,
                          p->partition_vcpu_memory_access);
  
  

•   if (p->uffd_mode) {
  

•   uffd_threads_needed = p->uffd_mode && !p->use_uffd_sigbus;
  

•   if (uffd_threads_needed) {
  

•           // Handler threads are not necessary when using
  

•           // UFFD_FEATURE_SIGBUS.
            uffd_handler_threads =
                    malloc(nr_vcpus * sizeof(*uffd_handler_threads));
            TEST_ASSERT(uffd_handler_threads, "Memory allocation failed");
  

@@ -322,6 +374,21 @@ static void run_test(enum vm_guest_mode mode, void *arg)

            pipefds = malloc(sizeof(int) * nr_vcpus * 2);
            TEST_ASSERT(pipefds, "Unable to allocate memory for pipefd");

•   }
  

•   if (p->use_uffd_sigbus) {
  

•           struct sigaction action;
  

•           memset(&action, 0, sizeof(action));
  

•           action.sa_sigaction = handle_uffd_sigbus;
  

•           action.sa_flags = SA_SIGINFO;
  

•           if (sigaction(SIGBUS, &action, NULL) < 0) {
  

•                   perror("Failed to set sigaction");
  

•                   return;
  

•           }
  

•   }
  

•   if (p->uffd_mode) {
  
            for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
                    vm_paddr_t vcpu_gpa;
  

@@ -329,7 +396,6 @@ static void run_test(enum vm_guest_mode mode, void *arg) void *vcpu_alias; uint64_t vcpu_mem_size;

•                   if (p->partition_vcpu_memory_access) {
                            vcpu_gpa = guest_test_phys_mem +
                                       (vcpu_id * guest_percpu_mem_size);
  

@@ -339,7 +405,8 @@ static void run_test(enum vm_guest_mode mode, void *arg) vcpu_mem_size = guest_percpu_mem_size * nr_vcpus; } PER_VCPU_DEBUG("Added VCPU %d with test mem gpa [%lx, %lx)\n",

•                                  vcpu_id, vcpu_gpa, vcpu_gpa + vcpu_mem_size);
  

•                                  vcpu_id, vcpu_gpa,
  

•                                  vcpu_gpa + vcpu_mem_size);
  
                    /* Cache the host addresses of the region */
                    vcpu_hva = addr_gpa2hva(vm, vcpu_gpa);
  

@@ -349,28 +416,39 @@ static void run_test(enum vm_guest_mode mode, void *arg) * Set up user fault fd to handle demand paging * requests. */

•                   r = pipe2(&pipefds[vcpu_id * 2],
  

•                             O_CLOEXEC | O_NONBLOCK);
  

•                   TEST_ASSERT(!r, "Failed to set up pipefd");
  

•                   setup_demand_paging(vm, &uffd_handler_threads[vcpu_id],
  

•                                       pipefds[vcpu_id * 2], p->uffd_mode,
  

•                                       p->uffd_delay, &uffd_args[vcpu_id],
  

•                                       vcpu_hva, vcpu_alias,
  

•                                       vcpu_mem_size);
  

•                   r = create_userfaultfd(p->uffd_mode, p->use_uffd_sigbus,
  

•                                          vcpu_hva, vcpu_alias,
  

•                                          vcpu_mem_size);
  

•                   if (r < 0)
  

•                           exit(-r);
  

•                   if (uffd_threads_needed) {
  

•                           start_uffd_thread(&uffd_handler_threads[vcpu_id],
  

•                                             &pipefds[vcpu_id * 2],
  

•                                             r, p->uffd_mode, p->uffd_delay,
  

•                                             &uffd_args[vcpu_id]);
  

•                           PER_VCPU_DEBUG("Created uffd thread for HVA range [%p, %p)\n",
  

•                                          vcpu_hva, vcpu_hva + vcpu_mem_size);
  

•                   }
  

•                   vcpu_worker_args[vcpu_id].uffd = r;
            }
    }
  
    /* Export the shared variables to the guest */
    sync_global_to_guest(vm, perf_test_args);
  
  

•   pr_info("Finished creating vCPUs and starting uffd threads\n");
  

•   pr_info("Finished creating vCPUs\n");
  
    clock_gettime(CLOCK_MONOTONIC, &start);
  
    for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
  

•           vcpu_worker_args[vcpu_id].vcpu_args =
  

•                           &perf_test_args.vcpu_args[vcpu_id];
  

•           vcpu_worker_args[vcpu_id].use_uffd_sigbus = p->use_uffd_sigbus;
  

•           vcpu_worker_args[vcpu_id].uffd_mode = p->uffd_mode;
            pthread_create(&vcpu_threads[vcpu_id], NULL, vcpu_worker,
  

•                          &perf_test_args.vcpu_args[vcpu_id]);
  

•                          &vcpu_worker_args[vcpu_id]);
    }
  
    pr_info("Started all vCPUs\n");
  

@@ -385,7 +463,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)

    pr_info("All vCPU threads joined\n");

•   if (p->uffd_mode) {
  

•   if (uffd_threads_needed) {
            char c;
  
            /* Tell the user fault fd handler threads to quit */
  

@@ -407,7 +485,8 @@ static void run_test(enum vm_guest_mode mode, void *arg)

    free(guest_data_prototype);
    free(vcpu_threads);

•   if (p->uffd_mode) {
  

•   free(vcpu_worker_args);
  

•   if (uffd_threads_needed) {
            free(uffd_handler_threads);
            free(uffd_args);
            free(pipefds);
  

@@ -417,11 +496,12 @@ static void run_test(enum vm_guest_mode mode, void *arg) static void help(char *name) { puts("");

•   printf("usage: %s [-h] [-m mode] [-u mode] [-d uffd_delay_usec]\n"
  

•   printf("usage: %s [-h] [-m mode] [-u mode] [-s] [-d uffd_delay_usec]\n"
           "          [-b memory] [-t type] [-v vcpus] [-o]\n", name);
    guest_modes_help();
    printf(" -u: use userfaultfd to handle vCPU page faults. Mode is a\n"
           "     UFFD registration mode: 'MISSING' or 'MINOR'.\n");
  

•   printf(" -s: use UFFD_FEATURE_SIGBUS to perform page-ins.\n");
    printf(" -d: add a delay in usec to the User Fault\n"
           "     FD handler to simulate demand paging\n"
           "     overheads. Ignored without -u.\n");
  

@@ -448,7 +528,7 @@ int main(int argc, char *argv[])

    guest_modes_append_default();

•   while ((opt = getopt(argc, argv, "hm:u:d:b:t:v:o")) != -1) {
  

•   while ((opt = getopt(argc, argv, "hm:u:sd:b:t:v:o")) != -1) {
            switch (opt) {
            case 'm':
                    guest_modes_cmdline(optarg);
  

@@ -460,6 +540,9 @@ int main(int argc, char *argv[]) p.uffd_mode = UFFDIO_REGISTER_MODE_MINOR; TEST_ASSERT(p.uffd_mode, "UFFD mode must be 'MISSING' or 'MINOR'."); break;

•           case 's':
  

•                   p.use_uffd_sigbus = true;
  

•                   break;
            case 'd':
                    p.uffd_delay = strtoul(optarg, NULL, 0);
                    TEST_ASSERT(p.uffd_delay >= 0, "A negative UFFD delay is not supported.");
  

-- 2.31.1.751.gd2f1c929bd-goog