diff options
| -rw-r--r-- | Documentation/virt/kvm/devices/vcpu.rst | 41 | ||||
| -rw-r--r-- | tools/testing/selftests/kvm/.gitignore | 1 | ||||
| -rw-r--r-- | tools/testing/selftests/kvm/Makefile | 1 | ||||
| -rw-r--r-- | tools/testing/selftests/kvm/system_counter_offset_test.c | 132 |
4 files changed, 161 insertions, 14 deletions
diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst index 3b399d727c11..60a29972d3f1 100644 --- a/Documentation/virt/kvm/devices/vcpu.rst +++ b/Documentation/virt/kvm/devices/vcpu.rst @@ -184,37 +184,50 @@ TSC is then derived by the following equation: guest_tsc = host_tsc + KVM_VCPU_TSC_OFFSET -This attribute is useful for the precise migration of a guest's TSC. The -following describes a possible algorithm to use for the migration of a -guest's TSC: +This attribute is useful to adjust the guest's TSC on live migration, +so that the TSC counts the time during which the VM was paused. The +following describes a possible algorithm to use for this purpose. From the source VMM process: -1. Invoke the KVM_GET_CLOCK ioctl to record the host TSC (t_0), - kvmclock nanoseconds (k_0), and realtime nanoseconds (r_0). +1. Invoke the KVM_GET_CLOCK ioctl to record the host TSC (tsc_src), + kvmclock nanoseconds (guest_src), and host CLOCK_REALTIME nanoseconds + (host_src). 2. Read the KVM_VCPU_TSC_OFFSET attribute for every vCPU to record the - guest TSC offset (off_n). + guest TSC offset (ofs_src[i]). 3. Invoke the KVM_GET_TSC_KHZ ioctl to record the frequency of the guest's TSC (freq). From the destination VMM process: -4. Invoke the KVM_SET_CLOCK ioctl, providing the kvmclock nanoseconds - (k_0) and realtime nanoseconds (r_0) in their respective fields. - Ensure that the KVM_CLOCK_REALTIME flag is set in the provided - structure. KVM will advance the VM's kvmclock to account for elapsed - time since recording the clock values. +4. Invoke the KVM_SET_CLOCK ioctl, providing the source nanoseconds from + kvmclock (guest_src) and CLOCK_REALTIME (host_src) in their respective + fields. Ensure that the KVM_CLOCK_REALTIME flag is set in the provided + structure. -5. Invoke the KVM_GET_CLOCK ioctl to record the host TSC (t_1) and - kvmclock nanoseconds (k_1). + KVM will advance the VM's kvmclock to account for elapsed time since + recording the clock values. Note that this will cause problems in + the guest (e.g., timeouts) unless CLOCK_REALTIME is synchronized + between the source and destination, and a reasonably short time passes + between the source pausing the VMs and the destination executing + steps 4-7. + +5. Invoke the KVM_GET_CLOCK ioctl to record the host TSC (tsc_dest) and + kvmclock nanoseconds (guest_dest). 6. Adjust the guest TSC offsets for every vCPU to account for (1) time elapsed since recording state and (2) difference in TSCs between the source and destination machine: - new_off_n = t_0 + off_n + (k_1 - k_0) * freq - t_1 + ofs_dst[i] = ofs_src[i] - + (guest_src - guest_dest) * freq + + (tsc_src - tsc_dest) + + ("ofs[i] + tsc - guest * freq" is the guest TSC value corresponding to + a time of 0 in kvmclock. The above formula ensures that it is the + same on the destination as it was on the source). 7. Write the KVM_VCPU_TSC_OFFSET attribute for every vCPU with the respective value derived in the previous step. diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore index 4bcff9c1a524..fdd13fbdcc8f 100644 --- a/tools/testing/selftests/kvm/.gitignore +++ b/tools/testing/selftests/kvm/.gitignore @@ -54,3 +54,4 @@ /set_memory_region_test /steal_time /kvm_binary_stats_test +/system_counter_offset_test diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile index 3995940d0011..fd20f271aac0 100644 --- a/tools/testing/selftests/kvm/Makefile +++ b/tools/testing/selftests/kvm/Makefile @@ -86,6 +86,7 @@ TEST_GEN_PROGS_x86_64 += rseq_test TEST_GEN_PROGS_x86_64 += set_memory_region_test TEST_GEN_PROGS_x86_64 += steal_time TEST_GEN_PROGS_x86_64 += kvm_binary_stats_test +TEST_GEN_PROGS_x86_64 += system_counter_offset_test TEST_GEN_PROGS_aarch64 += aarch64/debug-exceptions TEST_GEN_PROGS_aarch64 += aarch64/get-reg-list diff --git a/tools/testing/selftests/kvm/system_counter_offset_test.c b/tools/testing/selftests/kvm/system_counter_offset_test.c new file mode 100644 index 000000000000..b337bbbfa41f --- /dev/null +++ b/tools/testing/selftests/kvm/system_counter_offset_test.c @@ -0,0 +1,132 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2021, Google LLC. + * + * Tests for adjusting the system counter from userspace + */ +#include <asm/kvm_para.h> +#include <stdint.h> +#include <string.h> +#include <sys/stat.h> +#include <time.h> + +#include "test_util.h" +#include "kvm_util.h" +#include "processor.h" + +#define VCPU_ID 0 + +#ifdef __x86_64__ + +struct test_case { + uint64_t tsc_offset; +}; + +static struct test_case test_cases[] = { + { 0 }, + { 180 * NSEC_PER_SEC }, + { -180 * NSEC_PER_SEC }, +}; + +static void check_preconditions(struct kvm_vm *vm) +{ + if (!_vcpu_has_device_attr(vm, VCPU_ID, KVM_VCPU_TSC_CTRL, KVM_VCPU_TSC_OFFSET)) + return; + + print_skip("KVM_VCPU_TSC_OFFSET not supported; skipping test"); + exit(KSFT_SKIP); +} + +static void setup_system_counter(struct kvm_vm *vm, struct test_case *test) +{ + vcpu_access_device_attr(vm, VCPU_ID, KVM_VCPU_TSC_CTRL, + KVM_VCPU_TSC_OFFSET, &test->tsc_offset, true); +} + +static uint64_t guest_read_system_counter(struct test_case *test) +{ + return rdtsc(); +} + +static uint64_t host_read_guest_system_counter(struct test_case *test) +{ + return rdtsc() + test->tsc_offset; +} + +#else /* __x86_64__ */ + +#error test not implemented for this architecture! + +#endif + +#define GUEST_SYNC_CLOCK(__stage, __val) \ + GUEST_SYNC_ARGS(__stage, __val, 0, 0, 0) + +static void guest_main(void) +{ + int i; + + for (i = 0; i < ARRAY_SIZE(test_cases); i++) { + struct test_case *test = &test_cases[i]; + + GUEST_SYNC_CLOCK(i, guest_read_system_counter(test)); + } +} + +static void handle_sync(struct ucall *uc, uint64_t start, uint64_t end) +{ + uint64_t obs = uc->args[2]; + + TEST_ASSERT(start <= obs && obs <= end, + "unexpected system counter value: %"PRIu64" expected range: [%"PRIu64", %"PRIu64"]", + obs, start, end); + + pr_info("system counter value: %"PRIu64" expected range [%"PRIu64", %"PRIu64"]\n", + obs, start, end); +} + +static void handle_abort(struct ucall *uc) +{ + TEST_FAIL("%s at %s:%ld", (const char *)uc->args[0], + __FILE__, uc->args[1]); +} + +static void enter_guest(struct kvm_vm *vm) +{ + uint64_t start, end; + struct ucall uc; + int i; + + for (i = 0; i < ARRAY_SIZE(test_cases); i++) { + struct test_case *test = &test_cases[i]; + + setup_system_counter(vm, test); + start = host_read_guest_system_counter(test); + vcpu_run(vm, VCPU_ID); + end = host_read_guest_system_counter(test); + + switch (get_ucall(vm, VCPU_ID, &uc)) { + case UCALL_SYNC: + handle_sync(&uc, start, end); + break; + case UCALL_ABORT: + handle_abort(&uc); + return; + default: + TEST_ASSERT(0, "unhandled ucall %ld\n", + get_ucall(vm, VCPU_ID, &uc)); + } + } +} + +int main(void) +{ + struct kvm_vm *vm; + + vm = vm_create_default(VCPU_ID, 0, guest_main); + check_preconditions(vm); + ucall_init(vm, NULL); + + enter_guest(vm); + kvm_vm_free(vm); +} |