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

[James Houghton <jthoughton@google.com>]

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