1 files changed, 394 insertions, 0 deletions
diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
new file mode 100644
index 000000000000..76c583a07ea2
--- /dev/null
+++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
@@ -0,0 +1,394 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * access_tracking_perf_test
+ *
+ * Copyright (C) 2021, Google, Inc.
+ *
+ * This test measures the performance effects of KVM's access tracking.
+ * Access tracking is driven by the MMU notifiers test_young, clear_young, and
+ * clear_flush_young. These notifiers do not have a direct userspace API,
+ * however the clear_young notifier can be triggered by marking a pages as idle
+ * in /sys/kernel/mm/page_idle/bitmap. This test leverages that mechanism to
+ * enable access tracking on guest memory.
+ *
+ * To measure performance this test runs a VM with a configurable number of
+ * vCPUs that each touch every page in disjoint regions of memory. Performance
+ * is measured in the time it takes all vCPUs to finish touching their
+ * predefined region.
+ *
+ * Note that a deterministic correctness test of access tracking is not possible
+ * by using page_idle as it exists today. This is for a few reasons:
+ *
+ * 1. page_idle only issues clear_young notifiers, which lack a TLB flush. This
+ *    means subsequent guest accesses are not guaranteed to see page table
+ *    updates made by KVM until some time in the future.
+ *
+ * 2. page_idle only operates on LRU pages. Newly allocated pages are not
+ *    immediately allocated to LRU lists. Instead they are held in a "pagevec",
+ *    which is drained to LRU lists some time in the future. There is no
+ *    userspace API to force this drain to occur.
+ *
+ * These limitations are worked around in this test by using a large enough
+ * region of memory for each vCPU such that the number of translations cached in
+ * the TLB and the number of pages held in pagevecs are a small fraction of the
+ * overall workload. And if either of those conditions are not true (for example
+ * in nesting, where TLB size is unlimited) this test will print a warning
+ * rather than silently passing.
+ */
+#include <inttypes.h>
+#include <limits.h>
+#include <pthread.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include "kvm_util.h"
+#include "test_util.h"
+#include "perf_test_util.h"
+#include "guest_modes.h"
+
+/* Global variable used to synchronize all of the vCPU threads. */
+static int iteration;
+
+/* Defines what vCPU threads should do during a given iteration. */
+static enum {
+	/* Run the vCPU to access all its memory. */
+	ITERATION_ACCESS_MEMORY,
+	/* Mark the vCPU's memory idle in page_idle. */
+	ITERATION_MARK_IDLE,
+} iteration_work;
+
+/* Set to true when vCPU threads should exit. */
+static bool done;
+
+/* The iteration that was last completed by each vCPU. */
+static int vcpu_last_completed_iteration[KVM_MAX_VCPUS];
+
+/* Whether to overlap the regions of memory vCPUs access. */
+static bool overlap_memory_access;
+
+struct test_params {
+	/* The backing source for the region of memory. */
+	enum vm_mem_backing_src_type backing_src;
+
+	/* The amount of memory to allocate for each vCPU. */
+	uint64_t vcpu_memory_bytes;
+
+	/* The number of vCPUs to create in the VM. */
+	int nr_vcpus;
+};
+
+static uint64_t pread_uint64(int fd, const char *filename, uint64_t index)
+{
+	uint64_t value;
+	off_t offset = index * sizeof(value);
+
+	TEST_ASSERT(pread(fd, &value, sizeof(value), offset) == sizeof(value),
+		    "pread from %s offset 0x%" PRIx64 " failed!",
+		    filename, offset);
+
+	return value;
+
+}
+
+#define PAGEMAP_PRESENT (1ULL << 63)
+#define PAGEMAP_PFN_MASK ((1ULL << 55) - 1)
+
+static uint64_t lookup_pfn(int pagemap_fd, struct kvm_vm *vm, uint64_t gva)
+{
+	uint64_t hva = (uint64_t) addr_gva2hva(vm, gva);
+	uint64_t entry;
+	uint64_t pfn;
+
+	entry = pread_uint64(pagemap_fd, "pagemap", hva / getpagesize());
+	if (!(entry & PAGEMAP_PRESENT))
+		return 0;
+
+	pfn = entry & PAGEMAP_PFN_MASK;
+	__TEST_REQUIRE(pfn, "Looking up PFNs requires CAP_SYS_ADMIN");
+
+	return pfn;
+}
+
+static bool is_page_idle(int page_idle_fd, uint64_t pfn)
+{
+	uint64_t bits = pread_uint64(page_idle_fd, "page_idle", pfn / 64);
+
+	return !!((bits >> (pfn % 64)) & 1);
+}
+
+static void mark_page_idle(int page_idle_fd, uint64_t pfn)
+{
+	uint64_t bits = 1ULL << (pfn % 64);
+
+	TEST_ASSERT(pwrite(page_idle_fd, &bits, 8, 8 * (pfn / 64)) == 8,
+		    "Set page_idle bits for PFN 0x%" PRIx64, pfn);
+}
+
+static void mark_vcpu_memory_idle(struct kvm_vm *vm,
+				  struct perf_test_vcpu_args *vcpu_args)
+{
+	int vcpu_idx = vcpu_args->vcpu_idx;
+	uint64_t base_gva = vcpu_args->gva;
+	uint64_t pages = vcpu_args->pages;
+	uint64_t page;
+	uint64_t still_idle = 0;
+	uint64_t no_pfn = 0;
+	int page_idle_fd;
+	int pagemap_fd;
+
+	/* If vCPUs are using an overlapping region, let vCPU 0 mark it idle. */
+	if (overlap_memory_access && vcpu_idx)
+		return;
+
+	page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR);
+	TEST_ASSERT(page_idle_fd > 0, "Failed to open page_idle.");
+
+	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	TEST_ASSERT(pagemap_fd > 0, "Failed to open pagemap.");
+
+	for (page = 0; page < pages; page++) {
+		uint64_t gva = base_gva + page * perf_test_args.guest_page_size;
+		uint64_t pfn = lookup_pfn(pagemap_fd, vm, gva);
+
+		if (!pfn) {
+			no_pfn++;
+			continue;
+		}
+
+		if (is_page_idle(page_idle_fd, pfn)) {
+			still_idle++;
+			continue;
+		}
+
+		mark_page_idle(page_idle_fd, pfn);
+	}
+
+	/*
+	 * Assumption: Less than 1% of pages are going to be swapped out from
+	 * under us during this test.
+	 */
+	TEST_ASSERT(no_pfn < pages / 100,
+		    "vCPU %d: No PFN for %" PRIu64 " out of %" PRIu64 " pages.",
+		    vcpu_idx, no_pfn, pages);
+
+	/*
+	 * Check that at least 90% of memory has been marked idle (the rest
+	 * might not be marked idle because the pages have not yet made it to an
+	 * LRU list or the translations are still cached in the TLB). 90% is
+	 * arbitrary; high enough that we ensure most memory access went through
+	 * access tracking but low enough as to not make the test too brittle
+	 * over time and across architectures.
+	 *
+	 * Note that when run in nested virtualization, this check will trigger
+	 * much more frequently because TLB size is unlimited and since no flush
+	 * happens, much more pages are cached there and guest won't see the
+	 * "idle" bit cleared.
+	 */
+	if (still_idle < pages / 10)
+		printf("WARNING: vCPU%d: Too many pages still idle (%" PRIu64
+		       "out of %" PRIu64 "), this will affect performance results"
+		       ".\n",
+		       vcpu_idx, still_idle, pages);
+
+	close(page_idle_fd);
+	close(pagemap_fd);
+}
+
+static void assert_ucall(struct kvm_vcpu *vcpu, uint64_t expected_ucall)
+{
+	struct ucall uc;
+	uint64_t actual_ucall = get_ucall(vcpu, &uc);
+
+	TEST_ASSERT(expected_ucall == actual_ucall,
+		    "Guest exited unexpectedly (expected ucall %" PRIu64
+		    ", got %" PRIu64 ")",
+		    expected_ucall, actual_ucall);
+}
+
+static bool spin_wait_for_next_iteration(int *current_iteration)
+{
+	int last_iteration = *current_iteration;
+
+	do {
+		if (READ_ONCE(done))
+			return false;
+
+		*current_iteration = READ_ONCE(iteration);
+	} while (last_iteration == *current_iteration);
+
+	return true;
+}
+
+static void vcpu_thread_main(struct perf_test_vcpu_args *vcpu_args)
+{
+	struct kvm_vcpu *vcpu = vcpu_args->vcpu;
+	struct kvm_vm *vm = perf_test_args.vm;
+	int vcpu_idx = vcpu_args->vcpu_idx;
+	int current_iteration = 0;
+
+	while (spin_wait_for_next_iteration(&current_iteration)) {
+		switch (READ_ONCE(iteration_work)) {
+		case ITERATION_ACCESS_MEMORY:
+			vcpu_run(vcpu);
+			assert_ucall(vcpu, UCALL_SYNC);
+			break;
+		case ITERATION_MARK_IDLE:
+			mark_vcpu_memory_idle(vm, vcpu_args);
+			break;
+		};
+
+		vcpu_last_completed_iteration[vcpu_idx] = current_iteration;
+	}
+}
+
+static void spin_wait_for_vcpu(int vcpu_idx, int target_iteration)
+{
+	while (READ_ONCE(vcpu_last_completed_iteration[vcpu_idx]) !=
+	       target_iteration) {
+		continue;
+	}
+}
+
+/* The type of memory accesses to perform in the VM. */
+enum access_type {
+	ACCESS_READ,
+	ACCESS_WRITE,
+};
+
+static void run_iteration(struct kvm_vm *vm, int nr_vcpus, const char *description)
+{
+	struct timespec ts_start;
+	struct timespec ts_elapsed;
+	int next_iteration, i;
+
+	/* Kick off the vCPUs by incrementing iteration. */
+	next_iteration = ++iteration;
+
+	clock_gettime(CLOCK_MONOTONIC, &ts_start);
+
+	/* Wait for all vCPUs to finish the iteration. */
+	for (i = 0; i < nr_vcpus; i++)
+		spin_wait_for_vcpu(i, next_iteration);
+
+	ts_elapsed = timespec_elapsed(ts_start);
+	pr_info("%-30s: %ld.%09lds\n",
+		description, ts_elapsed.tv_sec, ts_elapsed.tv_nsec);
+}
+
+static void access_memory(struct kvm_vm *vm, int nr_vcpus,
+			  enum access_type access, const char *description)
+{
+	perf_test_set_wr_fract(vm, (access == ACCESS_READ) ? INT_MAX : 1);
+	iteration_work = ITERATION_ACCESS_MEMORY;
+	run_iteration(vm, nr_vcpus, description);
+}
+
+static void mark_memory_idle(struct kvm_vm *vm, int nr_vcpus)
+{
+	/*
+	 * Even though this parallelizes the work across vCPUs, this is still a
+	 * very slow operation because page_idle forces the test to mark one pfn
+	 * at a time and the clear_young notifier serializes on the KVM MMU
+	 * lock.
+	 */
+	pr_debug("Marking VM memory idle (slow)...\n");
+	iteration_work = ITERATION_MARK_IDLE;
+	run_iteration(vm, nr_vcpus, "Mark memory idle");
+}
+
+static void run_test(enum vm_guest_mode mode, void *arg)
+{
+	struct test_params *params = arg;
+	struct kvm_vm *vm;
+	int nr_vcpus = params->nr_vcpus;
+
+	vm = perf_test_create_vm(mode, nr_vcpus, params->vcpu_memory_bytes, 1,
+				 params->backing_src, !overlap_memory_access);
+
+	perf_test_start_vcpu_threads(nr_vcpus, vcpu_thread_main);
+
+	pr_info("\n");
+	access_memory(vm, nr_vcpus, ACCESS_WRITE, "Populating memory");
+
+	/* As a control, read and write to the populated memory first. */
+	access_memory(vm, nr_vcpus, ACCESS_WRITE, "Writing to populated memory");
+	access_memory(vm, nr_vcpus, ACCESS_READ, "Reading from populated memory");
+
+	/* Repeat on memory that has been marked as idle. */
+	mark_memory_idle(vm, nr_vcpus);
+	access_memory(vm, nr_vcpus, ACCESS_WRITE, "Writing to idle memory");
+	mark_memory_idle(vm, nr_vcpus);
+	access_memory(vm, nr_vcpus, ACCESS_READ, "Reading from idle memory");
+
+	/* Set done to signal the vCPU threads to exit */
+	done = true;
+
+	perf_test_join_vcpu_threads(nr_vcpus);
+	perf_test_destroy_vm(vm);
+}
+
+static void help(char *name)
+{
+	puts("");
+	printf("usage: %s [-h] [-m mode] [-b vcpu_bytes] [-v vcpus] [-o]  [-s mem_type]\n",
+	       name);
+	puts("");
+	printf(" -h: Display this help message.");
+	guest_modes_help();
+	printf(" -b: specify the size of the memory region which should be\n"
+	       "     dirtied by each vCPU. e.g. 10M or 3G.\n"
+	       "     (default: 1G)\n");
+	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");
+	backing_src_help("-s");
+	puts("");
+	exit(0);
+}
+
+int main(int argc, char *argv[])
+{
+	struct test_params params = {
+		.backing_src = DEFAULT_VM_MEM_SRC,
+		.vcpu_memory_bytes = DEFAULT_PER_VCPU_MEM_SIZE,
+		.nr_vcpus = 1,
+	};
+	int page_idle_fd;
+	int opt;
+
+	guest_modes_append_default();
+
+	while ((opt = getopt(argc, argv, "hm:b:v:os:")) != -1) {
+		switch (opt) {
+		case 'm':
+			guest_modes_cmdline(optarg);
+			break;
+		case 'b':
+			params.vcpu_memory_bytes = parse_size(optarg);
+			break;
+		case 'v':
+			params.nr_vcpus = atoi(optarg);
+			break;
+		case 'o':
+			overlap_memory_access = true;
+			break;
+		case 's':
+			params.backing_src = parse_backing_src_type(optarg);
+			break;
+		case 'h':
+		default:
+			help(argv[0]);
+			break;
+		}
+	}
+
+	page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR);
+	__TEST_REQUIRE(page_idle_fd >= 0,
+		       "CONFIG_IDLE_PAGE_TRACKING is not enabled");
+	close(page_idle_fd);
+
+	for_each_guest_mode(run_test, &params);
+
+	return 0;
+}