[PATCH v3 12/12] KVM: selftests: x86: Add vmx_nested_tsc_scaling_test

Ilias Stamatis
2021-05-21T10:29:09Z

Test that nested TSC scaling works as expected with both L1 and L2
scaled.

Signed-off-by: Ilias Stamatis <ilstam@amazon.com>
---
tools/testing/selftests/kvm/.gitignore | 1 +
tools/testing/selftests/kvm/Makefile | 1 +
.../kvm/x86_64/vmx_nested_tsc_scaling_test.c | 242 ++++++++++++++++++
3 files changed, 244 insertions(+)
create mode 100644 tools/testing/selftests/kvm/x86_64/vmx_nested_tsc_scaling_test.c

diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
index bd83158e0e0b..cc02022f9951 100644
--- a/tools/testing/selftests/kvm/.gitignore
+++ b/tools/testing/selftests/kvm/.gitignore
@@ -29,6 +29,7 @@
/x86_64/vmx_preemption_timer_test
/x86_64/vmx_set_nested_state_test
/x86_64/vmx_tsc_adjust_test
+/x86_64/vmx_nested_tsc_scaling_test
/x86_64/xapic_ipi_test
/x86_64/xen_shinfo_test
/x86_64/xen_vmcall_test
diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index e439d027939d..1078240b1313 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -60,6 +60,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/vmx_close_while_nested_test
TEST_GEN_PROGS_x86_64 += x86_64/vmx_dirty_log_test
TEST_GEN_PROGS_x86_64 += x86_64/vmx_set_nested_state_test
TEST_GEN_PROGS_x86_64 += x86_64/vmx_tsc_adjust_test
+TEST_GEN_PROGS_x86_64 += x86_64/vmx_nested_tsc_scaling_test
TEST_GEN_PROGS_x86_64 += x86_64/xapic_ipi_test
TEST_GEN_PROGS_x86_64 += x86_64/xss_msr_test
TEST_GEN_PROGS_x86_64 += x86_64/debug_regs
diff --git a/tools/testing/selftests/kvm/x86_64/vmx_nested_tsc_scaling_test.c b/tools/testing/selftests/kvm/x86_64/vmx_nested_tsc_scaling_test.c
new file mode 100644
index 000000000000..2c130250fe3b
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/vmx_nested_tsc_scaling_test.c
@@ -0,0 +1,242 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * vmx_nested_tsc_scaling_test
+ *
+ * Copyright (C) 2021 Amazon.com, Inc. or its affiliates.
+ *
+ * This test case verifies that nested TSC scaling behaves as expected when
+ * both L1 and L2 are scaled using different ratios. For this test we scale
+ * L1 down and scale L2 up.
+ */
+
+#include <time.h>
+
+#include "kvm_util.h"
+#include "vmx.h"
+#include "kselftest.h"
+
+
+#define VCPU_ID 0
+
+/* L2 is scaled up (from L1's perspective) by this factor */
+#define L2_SCALE_FACTOR 4ULL
+
+#define TSC_OFFSET_L2 ((uint64_t) -33125236320908)
+#define TSC_MULTIPLIER_L2 (L2_SCALE_FACTOR << 48)
+
+#define L2_GUEST_STACK_SIZE 64
+
+enum { USLEEP, UCHECK_L1, UCHECK_L2 };
+#define GUEST_SLEEP(sec) ucall(UCALL_SYNC, 2, USLEEP, sec)
+#define GUEST_CHECK(level, freq) ucall(UCALL_SYNC, 2, level, freq)
+
+
+/*
+ * This function checks whether the "actual" TSC frequency of a guest matches
+ * its expected frequency. In order to account for delays in taking the TSC
+ * measurements, a difference of 1% between the actual and the expected value
+ * is tolerated.
+ */
+static void compare_tsc_freq(uint64_t actual, uint64_t expected)
+{
+ uint64_t tolerance, thresh_low, thresh_high;
+
+ tolerance = expected / 100;
+ thresh_low = expected - tolerance;
+ thresh_high = expected + tolerance;
+
+ TEST_ASSERT(thresh_low < actual,
+ "TSC freq is expected to be between %"PRIu64" and %"PRIu64
+ " but it actually is %"PRIu64,
+ thresh_low, thresh_high, actual);
+ TEST_ASSERT(thresh_high > actual,
+ "TSC freq is expected to be between %"PRIu64" and %"PRIu64
+ " but it actually is %"PRIu64,
+ thresh_low, thresh_high, actual);
+}
+
+static void check_tsc_freq(int level)
+{
+ uint64_t tsc_start, tsc_end, tsc_freq;
+
+ /*
+ * Reading the TSC twice with about a second's difference should give
+ * us an approximation of the TSC frequency from the guest's
+ * perspective. Now, this won't be completely accurate, but it should
+ * be good enough for the purposes of this test.
+ */
+ tsc_start = rdmsr(MSR_IA32_TSC);
+ GUEST_SLEEP(1);
+ tsc_end = rdmsr(MSR_IA32_TSC);
+
+ tsc_freq = tsc_end - tsc_start;
+
+ GUEST_CHECK(level, tsc_freq);
+}
+
+static void l2_guest_code(void)
+{
+ check_tsc_freq(UCHECK_L2);
+
+ /* exit to L1 */
+ __asm__ __volatile__("vmcall");
+}
+
+static void l1_guest_code(struct vmx_pages *vmx_pages)
+{
+ unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
+ uint32_t control;
+
+ /* check that L1's frequency looks alright before launching L2 */
+ check_tsc_freq(UCHECK_L1);
+
+ GUEST_ASSERT(prepare_for_vmx_operation(vmx_pages));
+ GUEST_ASSERT(load_vmcs(vmx_pages));
+
+ /* prepare the VMCS for L2 execution */
+ prepare_vmcs(vmx_pages, l2_guest_code, &l2_guest_stack[L2_GUEST_STACK_SIZE]);
+
+ /* enable TSC offsetting and TSC scaling for L2 */
+ control = vmreadz(CPU_BASED_VM_EXEC_CONTROL);
+ control |= CPU_BASED_USE_MSR_BITMAPS | CPU_BASED_USE_TSC_OFFSETTING;
+ vmwrite(CPU_BASED_VM_EXEC_CONTROL, control);
+
+ control = vmreadz(SECONDARY_VM_EXEC_CONTROL);
+ control |= SECONDARY_EXEC_TSC_SCALING;
+ vmwrite(SECONDARY_VM_EXEC_CONTROL, control);
+
+ vmwrite(TSC_OFFSET, TSC_OFFSET_L2);
+ vmwrite(TSC_MULTIPLIER, TSC_MULTIPLIER_L2);
+ vmwrite(TSC_MULTIPLIER_HIGH, TSC_MULTIPLIER_L2 >> 32);
+
+ /* launch L2 */
+ GUEST_ASSERT(!vmlaunch());
+ GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_VMCALL);
+
+ /* check that L1's frequency still looks good */
+ check_tsc_freq(UCHECK_L1);
+
+ GUEST_DONE();
+}
+
+static void tsc_scaling_check_supported(void)
+{
+ if (!kvm_check_cap(KVM_CAP_TSC_CONTROL)) {
+ print_skip("TSC scaling not supported by the HW");
+ exit(KSFT_SKIP);
+ }
+}
+
+static void stable_tsc_check_supported(void)
+{
+ FILE *fp;
+ char buf[4];
+
+ fp = fopen("/sys/devices/system/clocksource/clocksource0/current_clocksource", "r");
+ if (fp == NULL)
+ goto skip_test;
+
+ if (fgets(buf, sizeof(buf), fp) == NULL)
+ goto skip_test;
+
+ if (strncmp(buf, "tsc", sizeof(buf)))
+ goto skip_test;
+
+ return;
+skip_test:
+ print_skip("TSC is not stable");
+ exit(KSFT_SKIP);
+}
+
+int main(int argc, char *argv[])
+{
+ struct kvm_vm *vm;
+ vm_vaddr_t vmx_pages_gva;
+
+ uint64_t tsc_start, tsc_end;
+ uint64_t tsc_khz;
+ uint64_t l1_scale_factor;
+ uint64_t l0_tsc_freq = 0;
+ uint64_t l1_tsc_freq = 0;
+ uint64_t l2_tsc_freq = 0;
+
+ nested_vmx_check_supported();
+ tsc_scaling_check_supported();
+ stable_tsc_check_supported();
+
+ /*
+ * We set L1's scale factor to be a random number from 2 to 10.
+ * Ideally we would do the same for L2's factor but that one is
+ * referenced by both main() and l1_guest_code() and using a global
+ * variable does not work.
+ */
+ srand(time(NULL));
+ l1_scale_factor = (rand() % 9) + 2;
+ printf("L1's scale down factor is: %"PRIu64"\n", l1_scale_factor);
+ printf("L2's scale up factor is: %llu\n", L2_SCALE_FACTOR);
+
+ tsc_start = rdtsc();
+ sleep(1);
+ tsc_end = rdtsc();
+
+ l0_tsc_freq = tsc_end - tsc_start;
+ printf("real TSC frequency is around: %"PRIu64"\n", l0_tsc_freq);
+
+ vm = vm_create_default(VCPU_ID, 0, (void *) l1_guest_code);
+ vcpu_alloc_vmx(vm, &vmx_pages_gva);
+ vcpu_args_set(vm, VCPU_ID, 1, vmx_pages_gva);
+
+ tsc_khz = _vcpu_ioctl(vm, VCPU_ID, KVM_GET_TSC_KHZ, NULL);
+ TEST_ASSERT(tsc_khz != -1, "vcpu ioctl KVM_GET_TSC_KHZ failed");
+
+ /* scale down L1's TSC frequency */
+ vcpu_ioctl(vm, VCPU_ID, KVM_SET_TSC_KHZ,
+ (void *) (tsc_khz / l1_scale_factor));
+
+ for (;;) {
+ volatile struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+ struct ucall uc;
+
+ vcpu_run(vm, VCPU_ID);
+ TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
+ "Got exit_reason other than KVM_EXIT_IO: %u (%s)\n",
+ run->exit_reason,
+ exit_reason_str(run->exit_reason));
+
+ switch (get_ucall(vm, VCPU_ID, &uc)) {
+ case UCALL_ABORT:
+ TEST_FAIL("%s", (const char *) uc.args[0]);
+ case UCALL_SYNC:
+ switch (uc.args[0]) {
+ case USLEEP:
+ sleep(uc.args[1]);
+ break;
+ case UCHECK_L1:
+ l1_tsc_freq = uc.args[1];
+ printf("L1's TSC frequency is around: %"PRIu64
+ "\n", l1_tsc_freq);
+
+ compare_tsc_freq(l1_tsc_freq,
+ l0_tsc_freq / l1_scale_factor);
+ break;
+ case UCHECK_L2:
+ l2_tsc_freq = uc.args[1];
+ printf("L2's TSC frequency is around: %"PRIu64
+ "\n", l2_tsc_freq);
+
+ compare_tsc_freq(l2_tsc_freq,
+ l1_tsc_freq * L2_SCALE_FACTOR);
+ break;
+ }
+ break;
+ case UCALL_DONE:
+ goto done;
+ default:
+ TEST_FAIL("Unknown ucall %lu", uc.cmd);
+ }
+ }
+
+done:
+ kvm_vm_free(vm);
+ return 0;
+}
--
2.17.1