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

Maxim Levitsky
2021-05-24T17:55:22Z

On Fri, 2021-05-21 at 11:24 +0100, Ilias Stamatis wrote:
> 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");

Tiny nitpick: I would print a message that expains the hack a bit better,
something like

"Kernel doesn't use TSC clocksource - assuming that host TSC is not stable - skipping test"

> + 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;
> +}

Overall looks good to me. Thanks!

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky