Commit df4ec5aa authored by Anish Moorthy's avatar Anish Moorthy Committed by Sean Christopherson
Browse files

KVM: selftests: Allow many vCPUs and reader threads per UFFD in demand paging test 



At the moment, demand_paging_test does not support profiling/testing
multiple vCPU threads concurrently faulting on a single uffd because

    (a) "-u" (run test in userfaultfd mode) creates a uffd for each vCPU's
        region, so that each uffd services a single vCPU thread.
    (b) "-u -o" (userfaultfd mode + overlapped vCPU memory accesses)
        simply doesn't work: the test tries to register the same memory
        to multiple uffds, causing an error.

Add support for many vcpus per uffd by
    (1) Keeping "-u" behavior unchanged.
    (2) Making "-u -a" create a single uffd for all of guest memory.
    (3) Making "-u -o" implicitly pass "-a", solving the problem in (b).
In cases (2) and (3) all vCPU threads fault on a single uffd.

With potentially multiple vCPUs per UFFD, it makes sense to allow
configuring the number of reader threads per UFFD as well: add the "-r"
flag to do so.

Signed-off-by: default avatarAnish Moorthy <amoorthy@google.com>
Acked-by: default avatarJames Houghton <jthoughton@google.com>
Link: https://lore.kernel.org/r/20240215235405.368539-12-amoorthy@google.com


[sean: fix kernel style violations, use calloc() for arrays]
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 2ca76c12

tools/testing/selftests/kvm/aarch64/page_fault_test.c

+2 −2
Original line number Diff line number Diff line
@@ -375,14 +375,14 @@ static void setup_uffd(struct kvm_vm *vm, struct test_params *p, 
		*pt_uffd = uffd_setup_demand_paging(uffd_mode, 0,

						    pt_args.hva,

						    pt_args.paging_size,

						    test->uffd_pt_handler);

						    1, test->uffd_pt_handler);



	*data_uffd = NULL;

	if (test->uffd_data_handler)

		*data_uffd = uffd_setup_demand_paging(uffd_mode, 0,

						      data_args.hva,

						      data_args.paging_size,

						      test->uffd_data_handler);

						      1, test->uffd_data_handler);

}



static void free_uffd(struct test_desc *test, struct uffd_desc *pt_uffd,

tools/testing/selftests/kvm/demand_paging_test.c

+63 −13
Original line number Diff line number Diff line
@@ -77,8 +77,20 @@ static int handle_uffd_page_request(int uffd_mode, int uffd, 
		copy.mode = 0;



		r = ioctl(uffd, UFFDIO_COPY, &copy);

		if (r == -1) {

			pr_info("Failed UFFDIO_COPY in 0x%lx from thread %d with errno: %d\n",

		/*

		 * 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;

		}
@@ -89,8 +101,20 @@ static int handle_uffd_page_request(int uffd_mode, int uffd, 
		cont.range.len = demand_paging_size;



		r = ioctl(uffd, UFFDIO_CONTINUE, &cont);

		if (r == -1) {

			pr_info("Failed UFFDIO_CONTINUE in 0x%lx from thread %d with errno: %d\n",

		/*

		 * 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;

		}
@@ -110,7 +134,9 @@ static int handle_uffd_page_request(int uffd_mode, int uffd, 


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;

};
@@ -131,11 +157,12 @@ 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;

	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);
@@ -148,7 +175,8 @@ static void run_test(enum vm_guest_mode mode, void *arg) 
	memset(guest_data_prototype, 0xAB, demand_paging_size);



	if (p->uffd_mode == UFFDIO_REGISTER_MODE_MINOR) {

		for (i = 0; i < nr_vcpus; i++) {

		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);
@@ -156,9 +184,13 @@ static void run_test(enum vm_guest_mode mode, void *arg) 
	}



	if (p->uffd_mode) {

		uffd_descs = malloc(nr_vcpus * sizeof(struct uffd_desc *));

		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 < nr_vcpus; i++) {

		for (i = 0; i < num_uffds; i++) {

			struct memstress_vcpu_args *vcpu_args;

			void *vcpu_hva;



			vcpu_args = &memstress_args.vcpu_args[i];
@@ -171,7 +203,8 @@ static void run_test(enum vm_guest_mode mode, void *arg) 
			 */

			uffd_descs[i] = uffd_setup_demand_paging(

				p->uffd_mode, p->uffd_delay, vcpu_hva,

				vcpu_args->pages * memstress_args.guest_page_size,

				uffd_region_size,

				p->readers_per_uffd,

				&handle_uffd_page_request);

		}

	}
@@ -188,7 +221,7 @@ static void run_test(enum vm_guest_mode mode, void *arg) 


	if (p->uffd_mode) {

		/* Tell the user fault fd handler threads to quit */

		for (i = 0; i < nr_vcpus; i++)

		for (i = 0; i < num_uffds; i++)

			uffd_stop_demand_paging(uffd_descs[i]);

	}
@@ -212,15 +245,20 @@ static void run_test(enum vm_guest_mode mode, void *arg) 
static void help(char *name)

{

	puts("");

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

	       "          [-b memory] [-s type] [-v vcpus] [-c cpu_list] [-o]\n", name);

	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");
@@ -239,12 +277,14 @@ int main(int argc, char *argv[]) 
	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, "hm:u:d:b:s:v:c:o")) != -1) {

	while ((opt = getopt(argc, argv, "ahom:u:d:b:s:v:c:r:")) != -1) {

		switch (opt) {

		case 'm':

			guest_modes_cmdline(optarg);
@@ -256,6 +296,9 @@ 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 '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.");
@@ -276,6 +319,13 @@ int main(int argc, char *argv[]) 
			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:

tools/testing/selftests/kvm/include/userfaultfd_util.h

+13 −3
Original line number Diff line number Diff line
@@ -17,17 +17,27 @@ 


typedef int (*uffd_handler_t)(int uffd_mode, int uffd, struct uffd_msg *msg);



struct uffd_desc {

struct uffd_reader_args {

	int uffd_mode;

	int uffd;

	int pipefds[2];

	useconds_t delay;

	uffd_handler_t handler;

	pthread_t thread;

	/* Holds the read end of the pipe for killing the reader. */

	int pipe;

};



struct uffd_desc {

	int uffd;

	uint64_t num_readers;

	/* Holds the write ends of the pipes for killing the readers. */

	int *pipefds;

	pthread_t *readers;

	struct uffd_reader_args *reader_args;

};



struct uffd_desc *uffd_setup_demand_paging(int uffd_mode, useconds_t delay,

					   void *hva, uint64_t len,

					   uint64_t num_readers,

					   uffd_handler_t handler);



void uffd_stop_demand_paging(struct uffd_desc *uffd);

tools/testing/selftests/kvm/lib/userfaultfd_util.c

+54 −27
Original line number Diff line number Diff line
@@ -27,10 +27,8 @@ 


static void *uffd_handler_thread_fn(void *arg)

{

	struct uffd_desc *uffd_desc = (struct uffd_desc *)arg;

	int uffd = uffd_desc->uffd;

	int pipefd = uffd_desc->pipefds[0];

	useconds_t delay = uffd_desc->delay;

	struct uffd_reader_args *reader_args = (struct uffd_reader_args *)arg;

	int uffd = reader_args->uffd;

	int64_t pages = 0;

	struct timespec start;

	struct timespec ts_diff;
@@ -44,7 +42,7 @@ static void *uffd_handler_thread_fn(void *arg) 


		pollfd[0].fd = uffd;

		pollfd[0].events = POLLIN;

		pollfd[1].fd = pipefd;

		pollfd[1].fd = reader_args->pipe;

		pollfd[1].events = POLLIN;



		r = poll(pollfd, 2, -1);
@@ -92,9 +90,9 @@ static void *uffd_handler_thread_fn(void *arg) 
		if (!(msg.event & UFFD_EVENT_PAGEFAULT))

			continue;



		if (delay)

			usleep(delay);

		r = uffd_desc->handler(uffd_desc->uffd_mode, uffd, &msg);

		if (reader_args->delay)

			usleep(reader_args->delay);

		r = reader_args->handler(reader_args->uffd_mode, uffd, &msg);

		if (r < 0)

			return NULL;

		pages++;
@@ -110,6 +108,7 @@ static void *uffd_handler_thread_fn(void *arg) 


struct uffd_desc *uffd_setup_demand_paging(int uffd_mode, useconds_t delay,

					   void *hva, uint64_t len,

					   uint64_t num_readers,

					   uffd_handler_t handler)

{

	struct uffd_desc *uffd_desc;
@@ -118,14 +117,25 @@ struct uffd_desc *uffd_setup_demand_paging(int uffd_mode, useconds_t delay, 
	struct uffdio_api uffdio_api;

	struct uffdio_register uffdio_register;

	uint64_t expected_ioctls = ((uint64_t) 1) << _UFFDIO_COPY;

	int ret;

	int ret, i;



	PER_PAGE_DEBUG("Userfaultfd %s mode, faults resolved with %s\n",

		       is_minor ? "MINOR" : "MISSING",

		       is_minor ? "UFFDIO_CONINUE" : "UFFDIO_COPY");



	uffd_desc = malloc(sizeof(struct uffd_desc));

	TEST_ASSERT(uffd_desc, "malloc failed");

	TEST_ASSERT(uffd_desc, "Failed to malloc uffd descriptor");



	uffd_desc->pipefds = calloc(sizeof(int), num_readers);

	TEST_ASSERT(uffd_desc->pipefds, "Failed to alloc pipes");



	uffd_desc->readers = calloc(sizeof(pthread_t), num_readers);

	TEST_ASSERT(uffd_desc->readers, "Failed to alloc reader threads");



	uffd_desc->reader_args = calloc(sizeof(struct uffd_reader_args), num_readers);

	TEST_ASSERT(uffd_desc->reader_args, "Failed to alloc reader_args");



	uffd_desc->num_readers = num_readers;



	/* In order to get minor faults, prefault via the alias. */

	if (is_minor)
@@ -148,18 +158,28 @@ struct uffd_desc *uffd_setup_demand_paging(int uffd_mode, useconds_t delay, 
	TEST_ASSERT((uffdio_register.ioctls & expected_ioctls) ==

		    expected_ioctls, "missing userfaultfd ioctls");



	ret = pipe2(uffd_desc->pipefds, O_CLOEXEC | O_NONBLOCK);

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



	uffd_desc->uffd_mode = uffd_mode;

	uffd_desc->uffd = uffd;

	uffd_desc->delay = delay;

	uffd_desc->handler = handler;

	pthread_create(&uffd_desc->thread, NULL, uffd_handler_thread_fn,

		       uffd_desc);

	for (i = 0; i < uffd_desc->num_readers; ++i) {

		int pipes[2];



		ret = pipe2((int *) &pipes, O_CLOEXEC | O_NONBLOCK);

		TEST_ASSERT(!ret, "Failed to set up pipefd %i for uffd_desc %p",

			    i, uffd_desc);



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

		       hva, hva + len);

		uffd_desc->pipefds[i] = pipes[1];



		uffd_desc->reader_args[i].uffd_mode = uffd_mode;

		uffd_desc->reader_args[i].uffd = uffd;

		uffd_desc->reader_args[i].delay = delay;

		uffd_desc->reader_args[i].handler = handler;

		uffd_desc->reader_args[i].pipe = pipes[0];



		pthread_create(&uffd_desc->readers[i], NULL, uffd_handler_thread_fn,

			       &uffd_desc->reader_args[i]);



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

			       i, hva, hva + len);

	}



	return uffd_desc;

}
@@ -167,19 +187,26 @@ struct uffd_desc *uffd_setup_demand_paging(int uffd_mode, useconds_t delay, 
void uffd_stop_demand_paging(struct uffd_desc *uffd)

{

	char c = 0;

	int ret;

	int i;



	ret = write(uffd->pipefds[1], &c, 1);

	TEST_ASSERT(ret == 1, "Unable to write to pipefd");

	for (i = 0; i < uffd->num_readers; ++i)

		TEST_ASSERT(write(uffd->pipefds[i], &c, 1) == 1,

			    "Unable to write to pipefd %i for uffd_desc %p", i, uffd);



	ret = pthread_join(uffd->thread, NULL);

	TEST_ASSERT(ret == 0, "Pthread_join failed.");

	for (i = 0; i < uffd->num_readers; ++i)

		TEST_ASSERT(!pthread_join(uffd->readers[i], NULL),

			    "Pthread_join failed on reader %i for uffd_desc %p", i, uffd);



	close(uffd->uffd);



	close(uffd->pipefds[1]);

	close(uffd->pipefds[0]);

	for (i = 0; i < uffd->num_readers; ++i) {

		close(uffd->pipefds[i]);

		close(uffd->reader_args[i].pipe);

	}



	free(uffd->pipefds);

	free(uffd->readers);

	free(uffd->reader_args);

	free(uffd);

}