From b58c55d522b256fa54c5e9175cf3202bc452b20e Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Sat, 26 Feb 2022 00:15:46 +0000 Subject: [PATCH] KVM: selftests: Add test to populate a VM with the max possible guest mem Add a selftest that enables populating a VM with the maximum amount of guest memory allowed by the underlying architecture. Abuse KVM's memslots by mapping a single host memory region into multiple memslots so that the selftest doesn't require a system with terabytes of RAM. Default to 512gb of guest memory, which isn't all that interesting, but should work on all MMUs and doesn't take an exorbitant amount of memory or time. E.g. testing with ~64tb of guest memory takes the better part of an hour, and requires 200gb of memory for KVM's page tables when using 4kb pages. To inflicit maximum abuse on KVM' MMU, default to 4kb pages (or whatever the not-hugepage size is) in the backing store (memfd). Use memfd for the host backing store to ensure that hugepages are guaranteed when requested, and to give the user explicit control of the size of hugepage being tested. By default, spin up as many vCPUs as there are available to the selftest, and distribute the work of dirtying each 4kb chunk of memory across all vCPUs. Dirtying guest memory forces KVM to populate its page tables, and also forces KVM to write back accessed/dirty information to struct page when the guest memory is freed. On x86, perform two passes with a MMU context reset between each pass to coerce KVM into dropping all references to the MMU root, e.g. to emulate a vCPU dropping the last reference. Perform both passes and all rendezvous on all architectures in the hope that arm64 and s390x can gain similar shenanigans in the future. Measure and report the duration of each operation, which is helpful not only to verify the test is working as intended, but also to easily evaluate the performance differences different page sizes. Provide command line options to limit the amount of guest memory, set the size of each slot (i.e. of the host memory region), set the number of vCPUs, and to enable usage of hugepages. Signed-off-by: Sean Christopherson Message-Id: <20220226001546.360188-29-seanjc@google.com> Signed-off-by: Paolo Bonzini --- tools/testing/selftests/kvm/.gitignore | 1 + tools/testing/selftests/kvm/Makefile | 1 + .../testing/selftests/kvm/max_guest_memory_test.c | 292 +++++++++++++++++++++ 3 files changed, 294 insertions(+) create mode 100644 tools/testing/selftests/kvm/max_guest_memory_test.c diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore index 052ddfe..9b67343 100644 --- a/tools/testing/selftests/kvm/.gitignore +++ b/tools/testing/selftests/kvm/.gitignore @@ -58,6 +58,7 @@ /hardware_disable_test /kvm_create_max_vcpus /kvm_page_table_test +/max_guest_memory_test /memslot_modification_stress_test /memslot_perf_test /rseq_test diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile index f7fa565..04099f4 100644 --- a/tools/testing/selftests/kvm/Makefile +++ b/tools/testing/selftests/kvm/Makefile @@ -93,6 +93,7 @@ TEST_GEN_PROGS_x86_64 += dirty_log_perf_test TEST_GEN_PROGS_x86_64 += hardware_disable_test TEST_GEN_PROGS_x86_64 += kvm_create_max_vcpus TEST_GEN_PROGS_x86_64 += kvm_page_table_test +TEST_GEN_PROGS_x86_64 += max_guest_memory_test TEST_GEN_PROGS_x86_64 += memslot_modification_stress_test TEST_GEN_PROGS_x86_64 += memslot_perf_test TEST_GEN_PROGS_x86_64 += rseq_test diff --git a/tools/testing/selftests/kvm/max_guest_memory_test.c b/tools/testing/selftests/kvm/max_guest_memory_test.c new file mode 100644 index 0000000..3875c4b --- /dev/null +++ b/tools/testing/selftests/kvm/max_guest_memory_test.c @@ -0,0 +1,292 @@ +// SPDX-License-Identifier: GPL-2.0 +#define _GNU_SOURCE + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "kvm_util.h" +#include "test_util.h" +#include "guest_modes.h" +#include "processor.h" + +static void guest_code(uint64_t start_gpa, uint64_t end_gpa, uint64_t stride) +{ + uint64_t gpa; + + for (gpa = start_gpa; gpa < end_gpa; gpa += stride) + *((volatile uint64_t *)gpa) = gpa; + + GUEST_DONE(); +} + +struct vcpu_info { + struct kvm_vm *vm; + uint32_t id; + uint64_t start_gpa; + uint64_t end_gpa; +}; + +static int nr_vcpus; +static atomic_t rendezvous; + +static void rendezvous_with_boss(void) +{ + int orig = atomic_read(&rendezvous); + + if (orig > 0) { + atomic_dec_and_test(&rendezvous); + while (atomic_read(&rendezvous) > 0) + cpu_relax(); + } else { + atomic_inc(&rendezvous); + while (atomic_read(&rendezvous) < 0) + cpu_relax(); + } +} + +static void run_vcpu(struct kvm_vm *vm, uint32_t vcpu_id) +{ + vcpu_run(vm, vcpu_id); + ASSERT_EQ(get_ucall(vm, vcpu_id, NULL), UCALL_DONE); +} + +static void *vcpu_worker(void *data) +{ + struct vcpu_info *vcpu = data; + struct kvm_vm *vm = vcpu->vm; + struct kvm_sregs sregs; + struct kvm_regs regs; + + vcpu_args_set(vm, vcpu->id, 3, vcpu->start_gpa, vcpu->end_gpa, + vm_get_page_size(vm)); + + /* Snapshot regs before the first run. */ + vcpu_regs_get(vm, vcpu->id, ®s); + rendezvous_with_boss(); + + run_vcpu(vm, vcpu->id); + rendezvous_with_boss(); + vcpu_regs_set(vm, vcpu->id, ®s); + vcpu_sregs_get(vm, vcpu->id, &sregs); +#ifdef __x86_64__ + /* Toggle CR0.WP to trigger a MMU context reset. */ + sregs.cr0 ^= X86_CR0_WP; +#endif + vcpu_sregs_set(vm, vcpu->id, &sregs); + rendezvous_with_boss(); + + run_vcpu(vm, vcpu->id); + rendezvous_with_boss(); + + return NULL; +} + +static pthread_t *spawn_workers(struct kvm_vm *vm, uint64_t start_gpa, + uint64_t end_gpa) +{ + struct vcpu_info *info; + uint64_t gpa, nr_bytes; + pthread_t *threads; + int i; + + threads = malloc(nr_vcpus * sizeof(*threads)); + TEST_ASSERT(threads, "Failed to allocate vCPU threads"); + + info = malloc(nr_vcpus * sizeof(*info)); + TEST_ASSERT(info, "Failed to allocate vCPU gpa ranges"); + + nr_bytes = ((end_gpa - start_gpa) / nr_vcpus) & + ~((uint64_t)vm_get_page_size(vm) - 1); + TEST_ASSERT(nr_bytes, "C'mon, no way you have %d CPUs", nr_vcpus); + + for (i = 0, gpa = start_gpa; i < nr_vcpus; i++, gpa += nr_bytes) { + info[i].vm = vm; + info[i].id = i; + info[i].start_gpa = gpa; + info[i].end_gpa = gpa + nr_bytes; + pthread_create(&threads[i], NULL, vcpu_worker, &info[i]); + } + return threads; +} + +static void rendezvous_with_vcpus(struct timespec *time, const char *name) +{ + int i, rendezvoused; + + pr_info("Waiting for vCPUs to finish %s...\n", name); + + rendezvoused = atomic_read(&rendezvous); + for (i = 0; abs(rendezvoused) != 1; i++) { + usleep(100); + if (!(i & 0x3f)) + pr_info("\r%d vCPUs haven't rendezvoused...", + abs(rendezvoused) - 1); + rendezvoused = atomic_read(&rendezvous); + } + + clock_gettime(CLOCK_MONOTONIC, time); + + /* Release the vCPUs after getting the time of the previous action. */ + pr_info("\rAll vCPUs finished %s, releasing...\n", name); + if (rendezvoused > 0) + atomic_set(&rendezvous, -nr_vcpus - 1); + else + atomic_set(&rendezvous, nr_vcpus + 1); +} + +static void calc_default_nr_vcpus(void) +{ + cpu_set_t possible_mask; + int r; + + r = sched_getaffinity(0, sizeof(possible_mask), &possible_mask); + TEST_ASSERT(!r, "sched_getaffinity failed, errno = %d (%s)", + errno, strerror(errno)); + + nr_vcpus = CPU_COUNT(&possible_mask) * 3/4; + TEST_ASSERT(nr_vcpus > 0, "Uh, no CPUs?"); +} + +int main(int argc, char *argv[]) +{ + /* + * Skip the first 4gb and slot0. slot0 maps <1gb and is used to back + * the guest's code, stack, and page tables. Because selftests creates + * an IRQCHIP, a.k.a. a local APIC, KVM creates an internal memslot + * just below the 4gb boundary. This test could create memory at + * 1gb-3gb,but it's simpler to skip straight to 4gb. + */ + const uint64_t size_1gb = (1 << 30); + const uint64_t start_gpa = (4ull * size_1gb); + const int first_slot = 1; + + struct timespec time_start, time_run1, time_reset, time_run2; + uint64_t max_gpa, gpa, slot_size, max_mem, i; + int max_slots, slot, opt, fd; + bool hugepages = false; + pthread_t *threads; + struct kvm_vm *vm; + void *mem; + + /* + * Default to 2gb so that maxing out systems with MAXPHADDR=46, which + * are quite common for x86, requires changing only max_mem (KVM allows + * 32k memslots, 32k * 2gb == ~64tb of guest memory). + */ + slot_size = 2 * size_1gb; + + max_slots = kvm_check_cap(KVM_CAP_NR_MEMSLOTS); + TEST_ASSERT(max_slots > first_slot, "KVM is broken"); + + /* All KVM MMUs should be able to survive a 128gb guest. */ + max_mem = 128 * size_1gb; + + calc_default_nr_vcpus(); + + while ((opt = getopt(argc, argv, "c:h:m:s:H")) != -1) { + switch (opt) { + case 'c': + nr_vcpus = atoi(optarg); + TEST_ASSERT(nr_vcpus > 0, "number of vcpus must be >0"); + break; + case 'm': + max_mem = atoi(optarg) * size_1gb; + TEST_ASSERT(max_mem > 0, "memory size must be >0"); + break; + case 's': + slot_size = atoi(optarg) * size_1gb; + TEST_ASSERT(slot_size > 0, "slot size must be >0"); + break; + case 'H': + hugepages = true; + break; + case 'h': + default: + printf("usage: %s [-c nr_vcpus] [-m max_mem_in_gb] [-s slot_size_in_gb] [-H]\n", argv[0]); + exit(1); + } + } + + vm = vm_create_default_with_vcpus(nr_vcpus, 0, 0, guest_code, NULL); + + max_gpa = vm_get_max_gfn(vm) << vm_get_page_shift(vm); + TEST_ASSERT(max_gpa > (4 * slot_size), "MAXPHYADDR <4gb "); + + fd = kvm_memfd_alloc(slot_size, hugepages); + mem = mmap(NULL, slot_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + TEST_ASSERT(mem != MAP_FAILED, "mmap() failed"); + + TEST_ASSERT(!madvise(mem, slot_size, MADV_NOHUGEPAGE), "madvise() failed"); + + /* Pre-fault the memory to avoid taking mmap_sem on guest page faults. */ + for (i = 0; i < slot_size; i += vm_get_page_size(vm)) + ((uint8_t *)mem)[i] = 0xaa; + + gpa = 0; + for (slot = first_slot; slot < max_slots; slot++) { + gpa = start_gpa + ((slot - first_slot) * slot_size); + if (gpa + slot_size > max_gpa) + break; + + if ((gpa - start_gpa) >= max_mem) + break; + + vm_set_user_memory_region(vm, slot, 0, gpa, slot_size, mem); + +#ifdef __x86_64__ + /* Identity map memory in the guest using 1gb pages. */ + for (i = 0; i < slot_size; i += size_1gb) + __virt_pg_map(vm, gpa + i, gpa + i, X86_PAGE_SIZE_1G); +#else + for (i = 0; i < slot_size; i += vm_get_page_size(vm)) + virt_pg_map(vm, gpa + i, gpa + i); +#endif + } + + atomic_set(&rendezvous, nr_vcpus + 1); + threads = spawn_workers(vm, start_gpa, gpa); + + pr_info("Running with %lugb of guest memory and %u vCPUs\n", + (gpa - start_gpa) / size_1gb, nr_vcpus); + + rendezvous_with_vcpus(&time_start, "spawning"); + rendezvous_with_vcpus(&time_run1, "run 1"); + rendezvous_with_vcpus(&time_reset, "reset"); + rendezvous_with_vcpus(&time_run2, "run 2"); + + time_run2 = timespec_sub(time_run2, time_reset); + time_reset = timespec_sub(time_reset, time_run1); + time_run1 = timespec_sub(time_run1, time_start); + + pr_info("run1 = %ld.%.9lds, reset = %ld.%.9lds, run2 = %ld.%.9lds\n", + time_run1.tv_sec, time_run1.tv_nsec, + time_reset.tv_sec, time_reset.tv_nsec, + time_run2.tv_sec, time_run2.tv_nsec); + + /* + * Delete even numbered slots (arbitrary) and unmap the first half of + * the backing (also arbitrary) to verify KVM correctly drops all + * references to the removed regions. + */ + for (slot = (slot - 1) & ~1ull; slot >= first_slot; slot -= 2) + vm_set_user_memory_region(vm, slot, 0, 0, 0, NULL); + + munmap(mem, slot_size / 2); + + /* Sanity check that the vCPUs actually ran. */ + for (i = 0; i < nr_vcpus; i++) + pthread_join(threads[i], NULL); + + /* + * Deliberately exit without deleting the remaining memslots or closing + * kvm_fd to test cleanup via mmu_notifier.release. + */ +} -- 2.7.4