[PATCH 2/2] KVM: selftests: Add UFFD_FEATURE_SIGBUS page-in tests
From: James Houghton
Date: Wed May 19 2021 - 17:04:56 EST
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@xxxxxxxxxx>
---
.../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