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    Subject[PATCH 2/2] KVM: selftests: Add UFFD_FEATURE_SIGBUS page-in tests
    From
    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 +++++++++++++-----
    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
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