1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * access_tracking_perf_test 4 * 5 * Copyright (C) 2021, Google, Inc. 6 * 7 * This test measures the performance effects of KVM's access tracking. 8 * Access tracking is driven by the MMU notifiers test_young, clear_young, and 9 * clear_flush_young. These notifiers do not have a direct userspace API, 10 * however the clear_young notifier can be triggered by marking a pages as idle 11 * in /sys/kernel/mm/page_idle/bitmap. This test leverages that mechanism to 12 * enable access tracking on guest memory. 13 * 14 * To measure performance this test runs a VM with a configurable number of 15 * vCPUs that each touch every page in disjoint regions of memory. Performance 16 * is measured in the time it takes all vCPUs to finish touching their 17 * predefined region. 18 * 19 * Note that a deterministic correctness test of access tracking is not possible 20 * by using page_idle as it exists today. This is for a few reasons: 21 * 22 * 1. page_idle only issues clear_young notifiers, which lack a TLB flush. This 23 * means subsequent guest accesses are not guaranteed to see page table 24 * updates made by KVM until some time in the future. 25 * 26 * 2. page_idle only operates on LRU pages. Newly allocated pages are not 27 * immediately allocated to LRU lists. Instead they are held in a "pagevec", 28 * which is drained to LRU lists some time in the future. There is no 29 * userspace API to force this drain to occur. 30 * 31 * These limitations are worked around in this test by using a large enough 32 * region of memory for each vCPU such that the number of translations cached in 33 * the TLB and the number of pages held in pagevecs are a small fraction of the 34 * overall workload. And if either of those conditions are not true (for example 35 * in nesting, where TLB size is unlimited) this test will print a warning 36 * rather than silently passing. 37 */ 38 #include <inttypes.h> 39 #include <limits.h> 40 #include <pthread.h> 41 #include <sys/mman.h> 42 #include <sys/types.h> 43 #include <sys/stat.h> 44 45 #include "kvm_util.h" 46 #include "test_util.h" 47 #include "memstress.h" 48 #include "guest_modes.h" 49 #include "processor.h" 50 51 /* Global variable used to synchronize all of the vCPU threads. */ 52 static int iteration; 53 54 /* Defines what vCPU threads should do during a given iteration. */ 55 static enum { 56 /* Run the vCPU to access all its memory. */ 57 ITERATION_ACCESS_MEMORY, 58 /* Mark the vCPU's memory idle in page_idle. */ 59 ITERATION_MARK_IDLE, 60 } iteration_work; 61 62 /* The iteration that was last completed by each vCPU. */ 63 static int vcpu_last_completed_iteration[KVM_MAX_VCPUS]; 64 65 /* Whether to overlap the regions of memory vCPUs access. */ 66 static bool overlap_memory_access; 67 68 struct test_params { 69 /* The backing source for the region of memory. */ 70 enum vm_mem_backing_src_type backing_src; 71 72 /* The amount of memory to allocate for each vCPU. */ 73 uint64_t vcpu_memory_bytes; 74 75 /* The number of vCPUs to create in the VM. */ 76 int nr_vcpus; 77 }; 78 pread_uint64(int fd,const char * filename,uint64_t index)79 static uint64_t pread_uint64(int fd, const char *filename, uint64_t index) 80 { 81 uint64_t value; 82 off_t offset = index * sizeof(value); 83 84 TEST_ASSERT(pread(fd, &value, sizeof(value), offset) == sizeof(value), 85 "pread from %s offset 0x%" PRIx64 " failed!", 86 filename, offset); 87 88 return value; 89 90 } 91 92 #define PAGEMAP_PRESENT (1ULL << 63) 93 #define PAGEMAP_PFN_MASK ((1ULL << 55) - 1) 94 lookup_pfn(int pagemap_fd,struct kvm_vm * vm,uint64_t gva)95 static uint64_t lookup_pfn(int pagemap_fd, struct kvm_vm *vm, uint64_t gva) 96 { 97 uint64_t hva = (uint64_t) addr_gva2hva(vm, gva); 98 uint64_t entry; 99 uint64_t pfn; 100 101 entry = pread_uint64(pagemap_fd, "pagemap", hva / getpagesize()); 102 if (!(entry & PAGEMAP_PRESENT)) 103 return 0; 104 105 pfn = entry & PAGEMAP_PFN_MASK; 106 __TEST_REQUIRE(pfn, "Looking up PFNs requires CAP_SYS_ADMIN"); 107 108 return pfn; 109 } 110 is_page_idle(int page_idle_fd,uint64_t pfn)111 static bool is_page_idle(int page_idle_fd, uint64_t pfn) 112 { 113 uint64_t bits = pread_uint64(page_idle_fd, "page_idle", pfn / 64); 114 115 return !!((bits >> (pfn % 64)) & 1); 116 } 117 mark_page_idle(int page_idle_fd,uint64_t pfn)118 static void mark_page_idle(int page_idle_fd, uint64_t pfn) 119 { 120 uint64_t bits = 1ULL << (pfn % 64); 121 122 TEST_ASSERT(pwrite(page_idle_fd, &bits, 8, 8 * (pfn / 64)) == 8, 123 "Set page_idle bits for PFN 0x%" PRIx64, pfn); 124 } 125 mark_vcpu_memory_idle(struct kvm_vm * vm,struct memstress_vcpu_args * vcpu_args)126 static void mark_vcpu_memory_idle(struct kvm_vm *vm, 127 struct memstress_vcpu_args *vcpu_args) 128 { 129 int vcpu_idx = vcpu_args->vcpu_idx; 130 uint64_t base_gva = vcpu_args->gva; 131 uint64_t pages = vcpu_args->pages; 132 uint64_t page; 133 uint64_t still_idle = 0; 134 uint64_t no_pfn = 0; 135 int page_idle_fd; 136 int pagemap_fd; 137 138 /* If vCPUs are using an overlapping region, let vCPU 0 mark it idle. */ 139 if (overlap_memory_access && vcpu_idx) 140 return; 141 142 page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR); 143 TEST_ASSERT(page_idle_fd > 0, "Failed to open page_idle."); 144 145 pagemap_fd = open("/proc/self/pagemap", O_RDONLY); 146 TEST_ASSERT(pagemap_fd > 0, "Failed to open pagemap."); 147 148 for (page = 0; page < pages; page++) { 149 uint64_t gva = base_gva + page * memstress_args.guest_page_size; 150 uint64_t pfn = lookup_pfn(pagemap_fd, vm, gva); 151 152 if (!pfn) { 153 no_pfn++; 154 continue; 155 } 156 157 if (is_page_idle(page_idle_fd, pfn)) { 158 still_idle++; 159 continue; 160 } 161 162 mark_page_idle(page_idle_fd, pfn); 163 } 164 165 /* 166 * Assumption: Less than 1% of pages are going to be swapped out from 167 * under us during this test. 168 */ 169 TEST_ASSERT(no_pfn < pages / 100, 170 "vCPU %d: No PFN for %" PRIu64 " out of %" PRIu64 " pages.", 171 vcpu_idx, no_pfn, pages); 172 173 /* 174 * Check that at least 90% of memory has been marked idle (the rest 175 * might not be marked idle because the pages have not yet made it to an 176 * LRU list or the translations are still cached in the TLB). 90% is 177 * arbitrary; high enough that we ensure most memory access went through 178 * access tracking but low enough as to not make the test too brittle 179 * over time and across architectures. 180 * 181 * When running the guest as a nested VM, "warn" instead of asserting 182 * as the TLB size is effectively unlimited and the KVM doesn't 183 * explicitly flush the TLB when aging SPTEs. As a result, more pages 184 * are cached and the guest won't see the "idle" bit cleared. 185 */ 186 if (still_idle >= pages / 10) { 187 #ifdef __x86_64__ 188 TEST_ASSERT(this_cpu_has(X86_FEATURE_HYPERVISOR), 189 "vCPU%d: Too many pages still idle (%lu out of %lu)", 190 vcpu_idx, still_idle, pages); 191 #endif 192 printf("WARNING: vCPU%d: Too many pages still idle (%lu out of %lu), " 193 "this will affect performance results.\n", 194 vcpu_idx, still_idle, pages); 195 } 196 197 close(page_idle_fd); 198 close(pagemap_fd); 199 } 200 assert_ucall(struct kvm_vcpu * vcpu,uint64_t expected_ucall)201 static void assert_ucall(struct kvm_vcpu *vcpu, uint64_t expected_ucall) 202 { 203 struct ucall uc; 204 uint64_t actual_ucall = get_ucall(vcpu, &uc); 205 206 TEST_ASSERT(expected_ucall == actual_ucall, 207 "Guest exited unexpectedly (expected ucall %" PRIu64 208 ", got %" PRIu64 ")", 209 expected_ucall, actual_ucall); 210 } 211 spin_wait_for_next_iteration(int * current_iteration)212 static bool spin_wait_for_next_iteration(int *current_iteration) 213 { 214 int last_iteration = *current_iteration; 215 216 do { 217 if (READ_ONCE(memstress_args.stop_vcpus)) 218 return false; 219 220 *current_iteration = READ_ONCE(iteration); 221 } while (last_iteration == *current_iteration); 222 223 return true; 224 } 225 vcpu_thread_main(struct memstress_vcpu_args * vcpu_args)226 static void vcpu_thread_main(struct memstress_vcpu_args *vcpu_args) 227 { 228 struct kvm_vcpu *vcpu = vcpu_args->vcpu; 229 struct kvm_vm *vm = memstress_args.vm; 230 int vcpu_idx = vcpu_args->vcpu_idx; 231 int current_iteration = 0; 232 233 while (spin_wait_for_next_iteration(¤t_iteration)) { 234 switch (READ_ONCE(iteration_work)) { 235 case ITERATION_ACCESS_MEMORY: 236 vcpu_run(vcpu); 237 assert_ucall(vcpu, UCALL_SYNC); 238 break; 239 case ITERATION_MARK_IDLE: 240 mark_vcpu_memory_idle(vm, vcpu_args); 241 break; 242 }; 243 244 vcpu_last_completed_iteration[vcpu_idx] = current_iteration; 245 } 246 } 247 spin_wait_for_vcpu(int vcpu_idx,int target_iteration)248 static void spin_wait_for_vcpu(int vcpu_idx, int target_iteration) 249 { 250 while (READ_ONCE(vcpu_last_completed_iteration[vcpu_idx]) != 251 target_iteration) { 252 continue; 253 } 254 } 255 256 /* The type of memory accesses to perform in the VM. */ 257 enum access_type { 258 ACCESS_READ, 259 ACCESS_WRITE, 260 }; 261 run_iteration(struct kvm_vm * vm,int nr_vcpus,const char * description)262 static void run_iteration(struct kvm_vm *vm, int nr_vcpus, const char *description) 263 { 264 struct timespec ts_start; 265 struct timespec ts_elapsed; 266 int next_iteration, i; 267 268 /* Kick off the vCPUs by incrementing iteration. */ 269 next_iteration = ++iteration; 270 271 clock_gettime(CLOCK_MONOTONIC, &ts_start); 272 273 /* Wait for all vCPUs to finish the iteration. */ 274 for (i = 0; i < nr_vcpus; i++) 275 spin_wait_for_vcpu(i, next_iteration); 276 277 ts_elapsed = timespec_elapsed(ts_start); 278 pr_info("%-30s: %ld.%09lds\n", 279 description, ts_elapsed.tv_sec, ts_elapsed.tv_nsec); 280 } 281 access_memory(struct kvm_vm * vm,int nr_vcpus,enum access_type access,const char * description)282 static void access_memory(struct kvm_vm *vm, int nr_vcpus, 283 enum access_type access, const char *description) 284 { 285 memstress_set_write_percent(vm, (access == ACCESS_READ) ? 0 : 100); 286 iteration_work = ITERATION_ACCESS_MEMORY; 287 run_iteration(vm, nr_vcpus, description); 288 } 289 mark_memory_idle(struct kvm_vm * vm,int nr_vcpus)290 static void mark_memory_idle(struct kvm_vm *vm, int nr_vcpus) 291 { 292 /* 293 * Even though this parallelizes the work across vCPUs, this is still a 294 * very slow operation because page_idle forces the test to mark one pfn 295 * at a time and the clear_young notifier serializes on the KVM MMU 296 * lock. 297 */ 298 pr_debug("Marking VM memory idle (slow)...\n"); 299 iteration_work = ITERATION_MARK_IDLE; 300 run_iteration(vm, nr_vcpus, "Mark memory idle"); 301 } 302 run_test(enum vm_guest_mode mode,void * arg)303 static void run_test(enum vm_guest_mode mode, void *arg) 304 { 305 struct test_params *params = arg; 306 struct kvm_vm *vm; 307 int nr_vcpus = params->nr_vcpus; 308 309 vm = memstress_create_vm(mode, nr_vcpus, params->vcpu_memory_bytes, 1, 310 params->backing_src, !overlap_memory_access); 311 312 memstress_start_vcpu_threads(nr_vcpus, vcpu_thread_main); 313 314 pr_info("\n"); 315 access_memory(vm, nr_vcpus, ACCESS_WRITE, "Populating memory"); 316 317 /* As a control, read and write to the populated memory first. */ 318 access_memory(vm, nr_vcpus, ACCESS_WRITE, "Writing to populated memory"); 319 access_memory(vm, nr_vcpus, ACCESS_READ, "Reading from populated memory"); 320 321 /* Repeat on memory that has been marked as idle. */ 322 mark_memory_idle(vm, nr_vcpus); 323 access_memory(vm, nr_vcpus, ACCESS_WRITE, "Writing to idle memory"); 324 mark_memory_idle(vm, nr_vcpus); 325 access_memory(vm, nr_vcpus, ACCESS_READ, "Reading from idle memory"); 326 327 memstress_join_vcpu_threads(nr_vcpus); 328 memstress_destroy_vm(vm); 329 } 330 help(char * name)331 static void help(char *name) 332 { 333 puts(""); 334 printf("usage: %s [-h] [-m mode] [-b vcpu_bytes] [-v vcpus] [-o] [-s mem_type]\n", 335 name); 336 puts(""); 337 printf(" -h: Display this help message."); 338 guest_modes_help(); 339 printf(" -b: specify the size of the memory region which should be\n" 340 " dirtied by each vCPU. e.g. 10M or 3G.\n" 341 " (default: 1G)\n"); 342 printf(" -v: specify the number of vCPUs to run.\n"); 343 printf(" -o: Overlap guest memory accesses instead of partitioning\n" 344 " them into a separate region of memory for each vCPU.\n"); 345 backing_src_help("-s"); 346 puts(""); 347 exit(0); 348 } 349 main(int argc,char * argv[])350 int main(int argc, char *argv[]) 351 { 352 struct test_params params = { 353 .backing_src = DEFAULT_VM_MEM_SRC, 354 .vcpu_memory_bytes = DEFAULT_PER_VCPU_MEM_SIZE, 355 .nr_vcpus = 1, 356 }; 357 int page_idle_fd; 358 int opt; 359 360 guest_modes_append_default(); 361 362 while ((opt = getopt(argc, argv, "hm:b:v:os:")) != -1) { 363 switch (opt) { 364 case 'm': 365 guest_modes_cmdline(optarg); 366 break; 367 case 'b': 368 params.vcpu_memory_bytes = parse_size(optarg); 369 break; 370 case 'v': 371 params.nr_vcpus = atoi_positive("Number of vCPUs", optarg); 372 break; 373 case 'o': 374 overlap_memory_access = true; 375 break; 376 case 's': 377 params.backing_src = parse_backing_src_type(optarg); 378 break; 379 case 'h': 380 default: 381 help(argv[0]); 382 break; 383 } 384 } 385 386 page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR); 387 __TEST_REQUIRE(page_idle_fd >= 0, 388 "CONFIG_IDLE_PAGE_TRACKING is not enabled"); 389 close(page_idle_fd); 390 391 for_each_guest_mode(run_test, ¶ms); 392 393 return 0; 394 } 395