tools/testing/selftests/kvm/demand_paging_test.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * KVM demand paging test
  * Adapted from dirty_log_test.c
  *
  * Copyright (C) 2018, Red Hat, Inc.
  * Copyright (C) 2019, Google, Inc.
  */
 #include <inttypes.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
 #include <pthread.h>
 #include <linux/userfaultfd.h>
 #include <sys/syscall.h>

 #include "kvm_util.h"
 #include "test_util.h"
 #include "memstress.h"
 #include "guest_modes.h"
 #include "ucall_common.h"
 #include "userfaultfd_util.h"

 #ifdef __NR_userfaultfd

 static int nr_vcpus = 1;
 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(struct memstress_vcpu_args *vcpu_args)
 {
 	struct kvm_vcpu *vcpu = vcpu_args->vcpu;
 	int vcpu_idx = vcpu_args->vcpu_idx;
 	struct kvm_run *run = vcpu->run;
 	struct timespec start;
 	struct timespec ts_diff;
 	int ret;

 	clock_gettime(CLOCK_MONOTONIC, &start);

 	/* Let the guest access its memory */
 	ret = _vcpu_run(vcpu);
 	TEST_ASSERT(ret == 0, "vcpu_run failed: %d", ret);
 	if (get_ucall(vcpu, NULL) != UCALL_SYNC) {
 		TEST_ASSERT(false,
 			    "Invalid guest sync status: exit_reason=%s",
 			    exit_reason_str(run->exit_reason));
 	}

 	ts_diff = timespec_elapsed(start);
 	PER_VCPU_DEBUG("vCPU %d execution time: %ld.%.9lds\n", vcpu_idx,
 		       ts_diff.tv_sec, ts_diff.tv_nsec);
 }

 static int handle_uffd_page_request(int uffd_mode, int uffd,
 		struct uffd_msg *msg)
 {
 	pid_t tid = syscall(__NR_gettid);
 	uint64_t addr = msg->arg.pagefault.address;
 	struct timespec start;
 	struct timespec ts_diff;
 	int r;

 	clock_gettime(CLOCK_MONOTONIC, &start);

 	if (uffd_mode == UFFDIO_REGISTER_MODE_MISSING) {
 		struct uffdio_copy copy;

 		copy.src = (uint64_t)guest_data_prototype;
 		copy.dst = addr;
 		copy.len = demand_paging_size;
 		copy.mode = 0;

 		r = ioctl(uffd, UFFDIO_COPY, &copy);
 		/*
 		 * With multiple vCPU threads fault on a single page and there are
 		 * multiple readers for the UFFD, at least one of the UFFDIO_COPYs
 		 * will fail with EEXIST: handle that case without signaling an
 		 * error.
 		 *
 		 * Note that this also suppress any EEXISTs occurring from,
 		 * e.g., the first UFFDIO_COPY/CONTINUEs on a page. That never
 		 * happens here, but a realistic VMM might potentially maintain
 		 * some external state to correctly surface EEXISTs to userspace
 		 * (or prevent duplicate COPY/CONTINUEs in the first place).
 		 */
 		if (r == -1 && errno != EEXIST) {
 			pr_info("Failed UFFDIO_COPY in 0x%lx from thread %d, errno = %d\n",
 				addr, tid, errno);
 			return r;
 		}
 	} else if (uffd_mode == UFFDIO_REGISTER_MODE_MINOR) {
 		struct uffdio_continue cont = {0};

 		cont.range.start = addr;
 		cont.range.len = demand_paging_size;

 		r = ioctl(uffd, UFFDIO_CONTINUE, &cont);
 		/*
 		 * With multiple vCPU threads fault on a single page and there are
 		 * multiple readers for the UFFD, at least one of the UFFDIO_COPYs
 		 * will fail with EEXIST: handle that case without signaling an
 		 * error.
 		 *
 		 * Note that this also suppress any EEXISTs occurring from,
 		 * e.g., the first UFFDIO_COPY/CONTINUEs on a page. That never
 		 * happens here, but a realistic VMM might potentially maintain
 		 * some external state to correctly surface EEXISTs to userspace
 		 * (or prevent duplicate COPY/CONTINUEs in the first place).
 		 */
 		if (r == -1 && errno != EEXIST) {
 			pr_info("Failed UFFDIO_CONTINUE in 0x%lx, thread %d, errno = %d\n",
 				addr, tid, errno);
 			return r;
 		}
 	} else {
 		TEST_FAIL("Invalid uffd mode %d", uffd_mode);
 	}

 	ts_diff = timespec_elapsed(start);

 	PER_PAGE_DEBUG("UFFD page-in %d \t%ld ns\n", tid,
 		       timespec_to_ns(ts_diff));
 	PER_PAGE_DEBUG("Paged in %ld bytes at 0x%lx from thread %d\n",
 		       demand_paging_size, addr, tid);

 	return 0;
 }

 struct test_params {
 	int uffd_mode;
 	bool single_uffd;
 	useconds_t uffd_delay;
 	int readers_per_uffd;
 	enum vm_mem_backing_src_type src_type;
 	bool partition_vcpu_memory_access;
 };

 static void prefault_mem(void *alias, uint64_t len)
 {
 	size_t p;

 	TEST_ASSERT(alias != NULL, "Alias required for minor faults");
 	for (p = 0; p < (len / demand_paging_size); ++p) {
 		memcpy(alias + (p * demand_paging_size),
 		       guest_data_prototype, demand_paging_size);
 	}
 }

 static void run_test(enum vm_guest_mode mode, void *arg)
 {
 	struct memstress_vcpu_args *vcpu_args;
 	struct test_params *p = arg;
 	struct uffd_desc **uffd_descs = NULL;
 	uint64_t uffd_region_size;
 	struct timespec start;
 	struct timespec ts_diff;
 	double vcpu_paging_rate;
 	struct kvm_vm *vm;
 	int i, num_uffds = 0;

 	vm = memstress_create_vm(mode, nr_vcpus, guest_percpu_mem_size, 1,
 				 p->src_type, p->partition_vcpu_memory_access);

 	demand_paging_size = get_backing_src_pagesz(p->src_type);

 	guest_data_prototype = malloc(demand_paging_size);
 	TEST_ASSERT(guest_data_prototype,
 		    "Failed to allocate buffer for guest data pattern");
 	memset(guest_data_prototype, 0xAB, demand_paging_size);

 	if (p->uffd_mode == UFFDIO_REGISTER_MODE_MINOR) {
 		num_uffds = p->single_uffd ? 1 : nr_vcpus;
 		for (i = 0; i < num_uffds; i++) {
 			vcpu_args = &memstress_args.vcpu_args[i];
 			prefault_mem(addr_gpa2alias(vm, vcpu_args->gpa),
 				     vcpu_args->pages * memstress_args.guest_page_size);
 		}
 	}

 	if (p->uffd_mode) {
 		num_uffds = p->single_uffd ? 1 : nr_vcpus;
 		uffd_region_size = nr_vcpus * guest_percpu_mem_size / num_uffds;

 		uffd_descs = malloc(num_uffds * sizeof(struct uffd_desc *));
 		TEST_ASSERT(uffd_descs, "Memory allocation failed");
 		for (i = 0; i < num_uffds; i++) {
 			struct memstress_vcpu_args *vcpu_args;
 			void *vcpu_hva;

 			vcpu_args = &memstress_args.vcpu_args[i];

 			/* Cache the host addresses of the region */
 			vcpu_hva = addr_gpa2hva(vm, vcpu_args->gpa);
 			/*
 			 * Set up user fault fd to handle demand paging
 			 * requests.
 			 */
 			uffd_descs[i] = uffd_setup_demand_paging(
 				p->uffd_mode, p->uffd_delay, vcpu_hva,
 				uffd_region_size,
 				p->readers_per_uffd,
 				&handle_uffd_page_request);
 		}
 	}

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

 	clock_gettime(CLOCK_MONOTONIC, &start);
 	memstress_start_vcpu_threads(nr_vcpus, vcpu_worker);
 	pr_info("Started all vCPUs\n");

 	memstress_join_vcpu_threads(nr_vcpus);
 	ts_diff = timespec_elapsed(start);
 	pr_info("All vCPU threads joined\n");

 	if (p->uffd_mode) {
 		/* Tell the user fault fd handler threads to quit */
 		for (i = 0; i < num_uffds; i++)
 			uffd_stop_demand_paging(uffd_descs[i]);
 	}

 	pr_info("Total guest execution time:\t%ld.%.9lds\n",
 		ts_diff.tv_sec, ts_diff.tv_nsec);

 	vcpu_paging_rate = memstress_args.vcpu_args[0].pages /
 			   ((double)ts_diff.tv_sec + (double)ts_diff.tv_nsec / NSEC_PER_SEC);
 	pr_info("Per-vcpu demand paging rate:\t%f pgs/sec/vcpu\n",
 		vcpu_paging_rate);
 	pr_info("Overall demand paging rate:\t%f pgs/sec\n",
 		vcpu_paging_rate * nr_vcpus);

 	memstress_destroy_vm(vm);

 	free(guest_data_prototype);
 	if (p->uffd_mode)
 		free(uffd_descs);
 }

 static void help(char *name)
 {
 	puts("");
 	printf("usage: %s [-h] [-m vm_mode] [-u uffd_mode] [-a]\n"
 		   "          [-d uffd_delay_usec] [-r readers_per_uffd] [-b memory]\n"
 		   "          [-s type] [-v vcpus] [-c cpu_list] [-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");
 	kvm_print_vcpu_pinning_help();
 	printf(" -a: Use a single userfaultfd for all of guest memory, instead of\n"
 	       "     creating one for each region paged by a unique vCPU\n"
 	       "     Set implicitly with -o, and no effect without -u.\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");
 	printf(" -r: Set the number of reader threads per uffd.\n");
 	printf(" -b: specify the size of the memory region which should be\n"
 	       "     demand paged by each vCPU. e.g. 10M or 3G.\n"
 	       "     Default: 1G\n");
 	backing_src_help("-s");
 	printf(" -v: specify the number of vCPUs to run.\n");
 	printf(" -o: Overlap guest memory accesses instead of partitioning\n"
 	       "     them into a separate region of memory for each vCPU.\n");
 	puts("");
 	exit(0);
 }

 int main(int argc, char *argv[])
 {
 	int max_vcpus = kvm_check_cap(KVM_CAP_MAX_VCPUS);
 	const char *cpulist = NULL;
 	struct test_params p = {
 		.src_type = DEFAULT_VM_MEM_SRC,
 		.partition_vcpu_memory_access = true,
 		.readers_per_uffd = 1,
 		.single_uffd = false,
 	};
 	int opt;

 	guest_modes_append_default();

 	while ((opt = getopt(argc, argv, "ahom:u:d:b:s:v:c:r:")) != -1) {
 		switch (opt) {
 		case 'm':
 			guest_modes_cmdline(optarg);
 			break;
 		case 'u':
 			if (!strcmp("MISSING", optarg))
 				p.uffd_mode = UFFDIO_REGISTER_MODE_MISSING;
 			else if (!strcmp("MINOR", optarg))
 				p.uffd_mode = UFFDIO_REGISTER_MODE_MINOR;
 			TEST_ASSERT(p.uffd_mode, "UFFD mode must be 'MISSING' or 'MINOR'.");
 			break;
 		case 'a':
 			p.single_uffd = true;
 			break;
 		case 'd':
 			p.uffd_delay = strtoul(optarg, NULL, 0);
 			TEST_ASSERT(p.uffd_delay >= 0, "A negative UFFD delay is not supported.");
 			break;
 		case 'b':
 			guest_percpu_mem_size = parse_size(optarg);
 			break;
 		case 's':
 			p.src_type = parse_backing_src_type(optarg);
 			break;
 		case 'v':
 			nr_vcpus = atoi_positive("Number of vCPUs", optarg);
 			TEST_ASSERT(nr_vcpus <= max_vcpus,
 				    "Invalid number of vcpus, must be between 1 and %d", max_vcpus);
 			break;
 		case 'c':
 			cpulist = optarg;
 			break;
 		case 'o':
 			p.partition_vcpu_memory_access = false;
 			p.single_uffd = true;
 			break;
 		case 'r':
 			p.readers_per_uffd = atoi(optarg);
 			TEST_ASSERT(p.readers_per_uffd >= 1,
 				    "Invalid number of readers per uffd %d: must be >=1",
 				    p.readers_per_uffd);
 			break;
 		case 'h':
 		default:
 			help(argv[0]);
 			break;
 		}
 	}

 	if (p.uffd_mode == UFFDIO_REGISTER_MODE_MINOR &&
 	    !backing_src_is_shared(p.src_type)) {
 		TEST_FAIL("userfaultfd MINOR mode requires shared memory; pick a different -s");
 	}

 	if (cpulist) {
 		kvm_parse_vcpu_pinning(cpulist, memstress_args.vcpu_to_pcpu,
 				       nr_vcpus);
 		memstress_args.pin_vcpus = true;
 	}

 	for_each_guest_mode(run_test, &p);

 	return 0;
 }

 #else /* __NR_userfaultfd */

 #warning "missing __NR_userfaultfd definition"

 int main(void)
 {
 	print_skip("__NR_userfaultfd must be present for userfaultfd test");
 	return KSFT_SKIP;
 }

 #endif /* __NR_userfaultfd */
	// SPDX-License-Identifier: GPL-2.0
	/*
	* KVM demand paging test
	* Adapted from dirty_log_test.c
	*
	* Copyright (C) 2018, Red Hat, Inc.
	* Copyright (C) 2019, Google, Inc.
	*/
	#include <inttypes.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <time.h>
	#include <pthread.h>
	#include <linux/userfaultfd.h>
	#include <sys/syscall.h>

	#include "kvm_util.h"
	#include "test_util.h"
	#include "memstress.h"
	#include "guest_modes.h"
	#include "ucall_common.h"
	#include "userfaultfd_util.h"

	#ifdef __NR_userfaultfd

	static int nr_vcpus = 1;
	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(struct memstress_vcpu_args *vcpu_args)
	{
	struct kvm_vcpu *vcpu = vcpu_args->vcpu;
	int vcpu_idx = vcpu_args->vcpu_idx;
	struct kvm_run *run = vcpu->run;
	struct timespec start;
	struct timespec ts_diff;
	int ret;

	clock_gettime(CLOCK_MONOTONIC, &start);

	/* Let the guest access its memory */
	ret = _vcpu_run(vcpu);
	TEST_ASSERT(ret == 0, "vcpu_run failed: %d", ret);
	if (get_ucall(vcpu, NULL) != UCALL_SYNC) {
	TEST_ASSERT(false,
	"Invalid guest sync status: exit_reason=%s",
	exit_reason_str(run->exit_reason));
	}

	ts_diff = timespec_elapsed(start);
	PER_VCPU_DEBUG("vCPU %d execution time: %ld.%.9lds\n", vcpu_idx,
	ts_diff.tv_sec, ts_diff.tv_nsec);
	}

	static int handle_uffd_page_request(int uffd_mode, int uffd,
	struct uffd_msg *msg)
	{
	pid_t tid = syscall(__NR_gettid);
	uint64_t addr = msg->arg.pagefault.address;
	struct timespec start;
	struct timespec ts_diff;
	int r;

	clock_gettime(CLOCK_MONOTONIC, &start);

	if (uffd_mode == UFFDIO_REGISTER_MODE_MISSING) {
	struct uffdio_copy copy;

	copy.src = (uint64_t)guest_data_prototype;
	copy.dst = addr;
	copy.len = demand_paging_size;
	copy.mode = 0;

	r = ioctl(uffd, UFFDIO_COPY, &copy);
	/*
	* With multiple vCPU threads fault on a single page and there are
	* multiple readers for the UFFD, at least one of the UFFDIO_COPYs
	* will fail with EEXIST: handle that case without signaling an
	* error.
	*
	* Note that this also suppress any EEXISTs occurring from,
	* e.g., the first UFFDIO_COPY/CONTINUEs on a page. That never
	* happens here, but a realistic VMM might potentially maintain
	* some external state to correctly surface EEXISTs to userspace
	* (or prevent duplicate COPY/CONTINUEs in the first place).
	*/
	if (r == -1 && errno != EEXIST) {
	pr_info("Failed UFFDIO_COPY in 0x%lx from thread %d, errno = %d\n",
	addr, tid, errno);
	return r;
	}
	} else if (uffd_mode == UFFDIO_REGISTER_MODE_MINOR) {
	struct uffdio_continue cont = {0};

	cont.range.start = addr;
	cont.range.len = demand_paging_size;

	r = ioctl(uffd, UFFDIO_CONTINUE, &cont);
	/*
	* With multiple vCPU threads fault on a single page and there are
	* multiple readers for the UFFD, at least one of the UFFDIO_COPYs
	* will fail with EEXIST: handle that case without signaling an
	* error.
	*
	* Note that this also suppress any EEXISTs occurring from,
	* e.g., the first UFFDIO_COPY/CONTINUEs on a page. That never
	* happens here, but a realistic VMM might potentially maintain
	* some external state to correctly surface EEXISTs to userspace
	* (or prevent duplicate COPY/CONTINUEs in the first place).
	*/
	if (r == -1 && errno != EEXIST) {
	pr_info("Failed UFFDIO_CONTINUE in 0x%lx, thread %d, errno = %d\n",
	addr, tid, errno);
	return r;
	}
	} else {
	TEST_FAIL("Invalid uffd mode %d", uffd_mode);
	}

	ts_diff = timespec_elapsed(start);

	PER_PAGE_DEBUG("UFFD page-in %d \t%ld ns\n", tid,
	timespec_to_ns(ts_diff));
	PER_PAGE_DEBUG("Paged in %ld bytes at 0x%lx from thread %d\n",
	demand_paging_size, addr, tid);

	return 0;
	}

	struct test_params {
	int uffd_mode;
	bool single_uffd;
	useconds_t uffd_delay;
	int readers_per_uffd;
	enum vm_mem_backing_src_type src_type;
	bool partition_vcpu_memory_access;
	};

	static void prefault_mem(void *alias, uint64_t len)
	{
	size_t p;

	TEST_ASSERT(alias != NULL, "Alias required for minor faults");
	for (p = 0; p < (len / demand_paging_size); ++p) {
	memcpy(alias + (p * demand_paging_size),
	guest_data_prototype, demand_paging_size);
	}
	}

	static void run_test(enum vm_guest_mode mode, void *arg)
	{
	struct memstress_vcpu_args *vcpu_args;
	struct test_params *p = arg;
	struct uffd_desc **uffd_descs = NULL;
	uint64_t uffd_region_size;
	struct timespec start;
	struct timespec ts_diff;
	double vcpu_paging_rate;
	struct kvm_vm *vm;
	int i, num_uffds = 0;

	vm = memstress_create_vm(mode, nr_vcpus, guest_percpu_mem_size, 1,
	p->src_type, p->partition_vcpu_memory_access);

	demand_paging_size = get_backing_src_pagesz(p->src_type);

	guest_data_prototype = malloc(demand_paging_size);
	TEST_ASSERT(guest_data_prototype,
	"Failed to allocate buffer for guest data pattern");
	memset(guest_data_prototype, 0xAB, demand_paging_size);

	if (p->uffd_mode == UFFDIO_REGISTER_MODE_MINOR) {
	num_uffds = p->single_uffd ? 1 : nr_vcpus;
	for (i = 0; i < num_uffds; i++) {
	vcpu_args = &memstress_args.vcpu_args[i];
	prefault_mem(addr_gpa2alias(vm, vcpu_args->gpa),
	vcpu_args->pages * memstress_args.guest_page_size);
	}
	}

	if (p->uffd_mode) {
	num_uffds = p->single_uffd ? 1 : nr_vcpus;
	uffd_region_size = nr_vcpus * guest_percpu_mem_size / num_uffds;

	uffd_descs = malloc(num_uffds * sizeof(struct uffd_desc *));
	TEST_ASSERT(uffd_descs, "Memory allocation failed");
	for (i = 0; i < num_uffds; i++) {
	struct memstress_vcpu_args *vcpu_args;
	void *vcpu_hva;

	vcpu_args = &memstress_args.vcpu_args[i];

	/* Cache the host addresses of the region */
	vcpu_hva = addr_gpa2hva(vm, vcpu_args->gpa);
	/*
	* Set up user fault fd to handle demand paging
	* requests.
	*/
	uffd_descs[i] = uffd_setup_demand_paging(
	p->uffd_mode, p->uffd_delay, vcpu_hva,
	uffd_region_size,
	p->readers_per_uffd,
	&handle_uffd_page_request);
	}
	}

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

	clock_gettime(CLOCK_MONOTONIC, &start);
	memstress_start_vcpu_threads(nr_vcpus, vcpu_worker);
	pr_info("Started all vCPUs\n");

	memstress_join_vcpu_threads(nr_vcpus);
	ts_diff = timespec_elapsed(start);
	pr_info("All vCPU threads joined\n");

	if (p->uffd_mode) {
	/* Tell the user fault fd handler threads to quit */
	for (i = 0; i < num_uffds; i++)
	uffd_stop_demand_paging(uffd_descs[i]);
	}

	pr_info("Total guest execution time:\t%ld.%.9lds\n",
	ts_diff.tv_sec, ts_diff.tv_nsec);

	vcpu_paging_rate = memstress_args.vcpu_args[0].pages /
	((double)ts_diff.tv_sec + (double)ts_diff.tv_nsec / NSEC_PER_SEC);
	pr_info("Per-vcpu demand paging rate:\t%f pgs/sec/vcpu\n",
	vcpu_paging_rate);
	pr_info("Overall demand paging rate:\t%f pgs/sec\n",
	vcpu_paging_rate * nr_vcpus);

	memstress_destroy_vm(vm);

	free(guest_data_prototype);
	if (p->uffd_mode)
	free(uffd_descs);
	}

	static void help(char *name)
	{
	puts("");
	printf("usage: %s [-h] [-m vm_mode] [-u uffd_mode] [-a]\n"
	" [-d uffd_delay_usec] [-r readers_per_uffd] [-b memory]\n"
	" [-s type] [-v vcpus] [-c cpu_list] [-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");
	kvm_print_vcpu_pinning_help();
	printf(" -a: Use a single userfaultfd for all of guest memory, instead of\n"
	" creating one for each region paged by a unique vCPU\n"
	" Set implicitly with -o, and no effect without -u.\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");
	printf(" -r: Set the number of reader threads per uffd.\n");
	printf(" -b: specify the size of the memory region which should be\n"
	" demand paged by each vCPU. e.g. 10M or 3G.\n"
	" Default: 1G\n");
	backing_src_help("-s");
	printf(" -v: specify the number of vCPUs to run.\n");
	printf(" -o: Overlap guest memory accesses instead of partitioning\n"
	" them into a separate region of memory for each vCPU.\n");
	puts("");
	exit(0);
	}

	int main(int argc, char *argv[])
	{
	int max_vcpus = kvm_check_cap(KVM_CAP_MAX_VCPUS);
	const char *cpulist = NULL;
	struct test_params p = {
	.src_type = DEFAULT_VM_MEM_SRC,
	.partition_vcpu_memory_access = true,
	.readers_per_uffd = 1,
	.single_uffd = false,
	};
	int opt;

	guest_modes_append_default();

	while ((opt = getopt(argc, argv, "ahom:u:d:b:s:v:c:r:")) != -1) {
	switch (opt) {
	case 'm':
	guest_modes_cmdline(optarg);
	break;
	case 'u':
	if (!strcmp("MISSING", optarg))
	p.uffd_mode = UFFDIO_REGISTER_MODE_MISSING;
	else if (!strcmp("MINOR", optarg))
	p.uffd_mode = UFFDIO_REGISTER_MODE_MINOR;
	TEST_ASSERT(p.uffd_mode, "UFFD mode must be 'MISSING' or 'MINOR'.");
	break;
	case 'a':
	p.single_uffd = true;
	break;
	case 'd':
	p.uffd_delay = strtoul(optarg, NULL, 0);
	TEST_ASSERT(p.uffd_delay >= 0, "A negative UFFD delay is not supported.");
	break;
	case 'b':
	guest_percpu_mem_size = parse_size(optarg);
	break;
	case 's':
	p.src_type = parse_backing_src_type(optarg);
	break;
	case 'v':
	nr_vcpus = atoi_positive("Number of vCPUs", optarg);
	TEST_ASSERT(nr_vcpus <= max_vcpus,
	"Invalid number of vcpus, must be between 1 and %d", max_vcpus);
	break;
	case 'c':
	cpulist = optarg;
	break;
	case 'o':
	p.partition_vcpu_memory_access = false;
	p.single_uffd = true;
	break;
	case 'r':
	p.readers_per_uffd = atoi(optarg);
	TEST_ASSERT(p.readers_per_uffd >= 1,
	"Invalid number of readers per uffd %d: must be >=1",
	p.readers_per_uffd);
	break;
	case 'h':
	default:
	help(argv[0]);
	break;
	}
	}

	if (p.uffd_mode == UFFDIO_REGISTER_MODE_MINOR &&
	!backing_src_is_shared(p.src_type)) {
	TEST_FAIL("userfaultfd MINOR mode requires shared memory; pick a different -s");
	}

	if (cpulist) {
	kvm_parse_vcpu_pinning(cpulist, memstress_args.vcpu_to_pcpu,
	nr_vcpus);
	memstress_args.pin_vcpus = true;
	}

	for_each_guest_mode(run_test, &p);

	return 0;
	}

	#else /* __NR_userfaultfd */

	#warning "missing __NR_userfaultfd definition"

	int main(void)
	{
	print_skip("__NR_userfaultfd must be present for userfaultfd test");
	return KSFT_SKIP;
	}

	#endif /* __NR_userfaultfd */