Re: [PATCH v2 01/11] KVM: selftests: Add a userfaultfd library

[Oliver Upton <oupton@google.com>]

HI Ricardo,

On Wed, Mar 23, 2022 at 03:53:55PM -0700, Ricardo Koller wrote:
> Move the generic userfaultfd code out of demand_paging_test.c into a
> common library, userfaultfd_util. This library consists of a setup and a
> stop function. The setup function starts a thread for handling page
> faults using the handler callback function. This setup returns a
> uffd_desc object which is then used in the stop function (to wait and
> destroy the threads).
> 
> Signed-off-by: Ricardo Koller <ricarkol@google.com>
> ---
>  tools/testing/selftests/kvm/Makefile          |   2 +-
>  .../selftests/kvm/demand_paging_test.c        | 227 +++---------------
>  .../selftests/kvm/include/userfaultfd_util.h  |  47 ++++
>  .../selftests/kvm/lib/userfaultfd_util.c      | 187 +++++++++++++++
>  4 files changed, 264 insertions(+), 199 deletions(-)
>  create mode 100644 tools/testing/selftests/kvm/include/userfaultfd_util.h
>  create mode 100644 tools/testing/selftests/kvm/lib/userfaultfd_util.c
> 
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 0e4926bc9a58..bc5f89b3700e 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -37,7 +37,7 @@ ifeq ($(ARCH),riscv)
>  	UNAME_M := riscv
>  endif
>  
> -LIBKVM = lib/assert.c lib/elf.c lib/io.c lib/kvm_util.c lib/rbtree.c lib/sparsebit.c lib/test_util.c lib/guest_modes.c lib/perf_test_util.c
> +LIBKVM = lib/assert.c lib/elf.c lib/io.c lib/kvm_util.c lib/rbtree.c lib/sparsebit.c lib/test_util.c lib/guest_modes.c lib/perf_test_util.c lib/userfaultfd_util.c
>  LIBKVM_x86_64 = lib/x86_64/apic.c lib/x86_64/processor.c lib/x86_64/vmx.c lib/x86_64/svm.c lib/x86_64/ucall.c lib/x86_64/handlers.S
>  LIBKVM_aarch64 = lib/aarch64/processor.c lib/aarch64/ucall.c lib/aarch64/handlers.S lib/aarch64/spinlock.c lib/aarch64/gic.c lib/aarch64/gic_v3.c lib/aarch64/vgic.c
>  LIBKVM_s390x = lib/s390x/processor.c lib/s390x/ucall.c lib/s390x/diag318_test_handler.c
> diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
> index 6a719d065599..b3d457cecd68 100644
> --- a/tools/testing/selftests/kvm/demand_paging_test.c
> +++ b/tools/testing/selftests/kvm/demand_paging_test.c
> @@ -22,23 +22,13 @@
>  #include "test_util.h"
>  #include "perf_test_util.h"
>  #include "guest_modes.h"
> +#include "userfaultfd_util.h"
>  
>  #ifdef __NR_userfaultfd
>  
> -#ifdef PRINT_PER_PAGE_UPDATES
> -#define PER_PAGE_DEBUG(...) printf(__VA_ARGS__)
> -#else
> -#define PER_PAGE_DEBUG(...) _no_printf(__VA_ARGS__)
> -#endif
> -
> -#ifdef PRINT_PER_VCPU_UPDATES
> -#define PER_VCPU_DEBUG(...) printf(__VA_ARGS__)
> -#else
> -#define PER_VCPU_DEBUG(...) _no_printf(__VA_ARGS__)
> -#endif
> -
>  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;
>  
> @@ -69,9 +59,11 @@ static void vcpu_worker(struct perf_test_vcpu_args *vcpu_args)
>  		       ts_diff.tv_sec, ts_diff.tv_nsec);
>  }
>  
> -static int handle_uffd_page_request(int uffd_mode, int uffd, uint64_t addr)
> +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;
> @@ -118,175 +110,32 @@ static int handle_uffd_page_request(int uffd_mode, int uffd, uint64_t addr)
>  	return 0;
>  }
>  
> -bool quit_uffd_thread;
> -
> -struct uffd_handler_args {
> +struct test_params {
>  	int uffd_mode;
> -	int uffd;
> -	int pipefd;
> -	useconds_t delay;
> +	useconds_t uffd_delay;
> +	enum vm_mem_backing_src_type src_type;
> +	bool partition_vcpu_memory_access;
>  };
>  
> -static void *uffd_handler_thread_fn(void *arg)
> +static void prefault_mem(void *alias, uint64_t len)
>  {
> -	struct uffd_handler_args *uffd_args = (struct uffd_handler_args *)arg;
> -	int uffd = uffd_args->uffd;
> -	int pipefd = uffd_args->pipefd;
> -	useconds_t delay = uffd_args->delay;
> -	int64_t pages = 0;
> -	struct timespec start;
> -	struct timespec ts_diff;
> -
> -	clock_gettime(CLOCK_MONOTONIC, &start);
> -	while (!quit_uffd_thread) {
> -		struct uffd_msg msg;
> -		struct pollfd pollfd[2];
> -		char tmp_chr;
> -		int r;
> -		uint64_t addr;
> -
> -		pollfd[0].fd = uffd;
> -		pollfd[0].events = POLLIN;
> -		pollfd[1].fd = pipefd;
> -		pollfd[1].events = POLLIN;
> -
> -		r = poll(pollfd, 2, -1);
> -		switch (r) {
> -		case -1:
> -			pr_info("poll err");
> -			continue;
> -		case 0:
> -			continue;
> -		case 1:
> -			break;
> -		default:
> -			pr_info("Polling uffd returned %d", r);
> -			return NULL;
> -		}
> -
> -		if (pollfd[0].revents & POLLERR) {
> -			pr_info("uffd revents has POLLERR");
> -			return NULL;
> -		}
> -
> -		if (pollfd[1].revents & POLLIN) {
> -			r = read(pollfd[1].fd, &tmp_chr, 1);
> -			TEST_ASSERT(r == 1,
> -				    "Error reading pipefd in UFFD thread\n");
> -			return NULL;
> -		}
> -
> -		if (!(pollfd[0].revents & POLLIN))
> -			continue;
> -
> -		r = read(uffd, &msg, sizeof(msg));
> -		if (r == -1) {
> -			if (errno == EAGAIN)
> -				continue;
> -			pr_info("Read of uffd got errno %d\n", errno);
> -			return NULL;
> -		}
> -
> -		if (r != sizeof(msg)) {
> -			pr_info("Read on uffd returned unexpected size: %d bytes", r);
> -			return NULL;
> -		}
> -
> -		if (!(msg.event & UFFD_EVENT_PAGEFAULT))
> -			continue;
> +	size_t p;
>  
> -		if (delay)
> -			usleep(delay);
> -		addr =  msg.arg.pagefault.address;
> -		r = handle_uffd_page_request(uffd_args->uffd_mode, uffd, addr);
> -		if (r < 0)
> -			return NULL;
> -		pages++;
> +	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);
>  	}
> -
> -	ts_diff = timespec_elapsed(start);
> -	PER_VCPU_DEBUG("userfaulted %ld pages over %ld.%.9lds. (%f/sec)\n",
> -		       pages, ts_diff.tv_sec, ts_diff.tv_nsec,
> -		       pages / ((double)ts_diff.tv_sec + (double)ts_diff.tv_nsec / 100000000.0));
> -
> -	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)
> -{
> -	bool is_minor = (uffd_mode == UFFDIO_REGISTER_MODE_MINOR);
> -	int uffd;
> -	struct uffdio_api uffdio_api;
> -	struct uffdio_register uffdio_register;
> -	uint64_t expected_ioctls = ((uint64_t) 1) << _UFFDIO_COPY;
> -
> -	PER_PAGE_DEBUG("Userfaultfd %s mode, faults resolved with %s\n",
> -		       is_minor ? "MINOR" : "MISSING",
> -		       is_minor ? "UFFDIO_CONINUE" : "UFFDIO_COPY");
> -
> -	/* In order to get minor faults, prefault via the alias. */
> -	if (is_minor) {
> -		size_t p;
> -
> -		expected_ioctls = ((uint64_t) 1) << _UFFDIO_CONTINUE;
> -
> -		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);
> -		}
> -	}
> -
> -	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
> -	TEST_ASSERT(uffd >= 0, "uffd creation failed, errno: %d", errno);
> -
> -	uffdio_api.api = UFFD_API;
> -	uffdio_api.features = 0;
> -	TEST_ASSERT(ioctl(uffd, UFFDIO_API, &uffdio_api) != -1,
> -		    "ioctl UFFDIO_API failed: %" PRIu64,
> -		    (uint64_t)uffdio_api.api);
> -
> -	uffdio_register.range.start = (uint64_t)hva;
> -	uffdio_register.range.len = len;
> -	uffdio_register.mode = uffd_mode;
> -	TEST_ASSERT(ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) != -1,
> -		    "ioctl UFFDIO_REGISTER failed");
> -	TEST_ASSERT((uffdio_register.ioctls & expected_ioctls) ==
> -		    expected_ioctls, "missing userfaultfd ioctls");
> -
> -	uffd_args->uffd_mode = uffd_mode;
> -	uffd_args->uffd = uffd;
> -	uffd_args->pipefd = pipefd;
> -	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;
> -	useconds_t uffd_delay;
> -	enum vm_mem_backing_src_type src_type;
> -	bool partition_vcpu_memory_access;
> -};
> -
>  static void run_test(enum vm_guest_mode mode, void *arg)
>  {
>  	struct test_params *p = arg;
> -	pthread_t *uffd_handler_threads = NULL;
> -	struct uffd_handler_args *uffd_args = NULL;
> +	struct uffd_desc **uffd_descs = NULL;
>  	struct timespec start;
>  	struct timespec ts_diff;
> -	int *pipefds = NULL;
>  	struct kvm_vm *vm;
>  	int vcpu_id;
> -	int r;
>  
>  	vm = perf_test_create_vm(mode, nr_vcpus, guest_percpu_mem_size, 1,
>  				 p->src_type, p->partition_vcpu_memory_access);
> @@ -299,15 +148,8 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>  	memset(guest_data_prototype, 0xAB, demand_paging_size);
>  
>  	if (p->uffd_mode) {
> -		uffd_handler_threads =
> -			malloc(nr_vcpus * sizeof(*uffd_handler_threads));
> -		TEST_ASSERT(uffd_handler_threads, "Memory allocation failed");
> -
> -		uffd_args = malloc(nr_vcpus * sizeof(*uffd_args));
> -		TEST_ASSERT(uffd_args, "Memory allocation failed");
> -
> -		pipefds = malloc(sizeof(int) * nr_vcpus * 2);
> -		TEST_ASSERT(pipefds, "Unable to allocate memory for pipefd");
> +		uffd_descs = malloc(nr_vcpus * sizeof(struct uffd_desc *));
> +		TEST_ASSERT(uffd_descs, "Memory allocation failed");
>  
>  		for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
>  			struct perf_test_vcpu_args *vcpu_args;
> @@ -320,19 +162,17 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>  			vcpu_hva = addr_gpa2hva(vm, vcpu_args->gpa);
>  			vcpu_alias = addr_gpa2alias(vm, vcpu_args->gpa);
>  
> +			prefault_mem(vcpu_alias,
> +				vcpu_args->pages * perf_test_args.guest_page_size);
> +
>  			/*
>  			 * 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_args->pages * perf_test_args.guest_page_size);
> +			uffd_descs[vcpu_id] = uffd_setup_demand_paging(
> +				p->uffd_mode, p->uffd_delay, vcpu_hva,
> +				vcpu_args->pages * perf_test_args.guest_page_size,
> +				&handle_uffd_page_request);
>  		}
>  	}
>  
> @@ -347,15 +187,9 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>  	pr_info("All vCPU threads joined\n");
>  
>  	if (p->uffd_mode) {
> -		char c;
> -
>  		/* Tell the user fault fd handler threads to quit */
> -		for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
> -			r = write(pipefds[vcpu_id * 2 + 1], &c, 1);
> -			TEST_ASSERT(r == 1, "Unable to write to pipefd");
> -
> -			pthread_join(uffd_handler_threads[vcpu_id], NULL);
> -		}
> +		for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++)
> +			uffd_stop_demand_paging(uffd_descs[vcpu_id]);
>  	}
>  
>  	pr_info("Total guest execution time: %ld.%.9lds\n",
> @@ -367,11 +201,8 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>  	perf_test_destroy_vm(vm);
>  
>  	free(guest_data_prototype);
> -	if (p->uffd_mode) {
> -		free(uffd_handler_threads);
> -		free(uffd_args);
> -		free(pipefds);
> -	}
> +	if (p->uffd_mode)
> +		free(uffd_descs);
>  }
>  
>  static void help(char *name)
> diff --git a/tools/testing/selftests/kvm/include/userfaultfd_util.h b/tools/testing/selftests/kvm/include/userfaultfd_util.h
> new file mode 100644
> index 000000000000..dffb4e768d56
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/include/userfaultfd_util.h
> @@ -0,0 +1,47 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KVM userfaultfd util
> + * Adapted from demand_paging_test.c
> + *
> + * Copyright (C) 2018, Red Hat, Inc.
> + * Copyright (C) 2019, Google, Inc.
> + * Copyright (C) 2022, Google, Inc.
> + */
> +
> +#define _GNU_SOURCE /* for pipe2 */
> +
> +#include <inttypes.h>
> +#include <time.h>
> +#include <pthread.h>
> +#include <linux/userfaultfd.h>
> +
> +#include "test_util.h"
> +
> +typedef int (*uffd_handler_t)(int uffd_mode, int uffd, struct uffd_msg *msg);
> +
> +struct uffd_desc {
> +	int uffd_mode;
> +	int uffd;
> +	int pipefds[2];
> +	useconds_t delay;
> +	uffd_handler_t handler;
> +	pthread_t thread;
> +};
> +
> +struct uffd_desc *uffd_setup_demand_paging(int uffd_mode,
> +		useconds_t uffd_delay, void *hva, uint64_t len,
> +		uffd_handler_t handler);
> +
> +void uffd_stop_demand_paging(struct uffd_desc *uffd);
> +
> +#ifdef PRINT_PER_PAGE_UPDATES
> +#define PER_PAGE_DEBUG(...) printf(__VA_ARGS__)
> +#else
> +#define PER_PAGE_DEBUG(...) _no_printf(__VA_ARGS__)
> +#endif
> +
> +#ifdef PRINT_PER_VCPU_UPDATES
> +#define PER_VCPU_DEBUG(...) printf(__VA_ARGS__)
> +#else
> +#define PER_VCPU_DEBUG(...) _no_printf(__VA_ARGS__)
> +#endif
> diff --git a/tools/testing/selftests/kvm/lib/userfaultfd_util.c b/tools/testing/selftests/kvm/lib/userfaultfd_util.c
> new file mode 100644
> index 000000000000..4395032ccbe4
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/lib/userfaultfd_util.c
> @@ -0,0 +1,187 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KVM userfaultfd util
> + * Adapted from demand_paging_test.c
> + *

nit: since this supplants the uffd code in demand_paging_test, there is
now little context to be found there. Maybe just elide this reference.

> + * Copyright (C) 2018, Red Hat, Inc.
> + * Copyright (C) 2019, Google, Inc.
> + * Copyright (C) 2022, Google, Inc.

No lawyer, but this is what our employer recommends for copyright:

Copyright (C) 2019-2022 Google LLC

Otherwise:

Reviewed-by: Oliver Upton <oupton@google.com>
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