// SPDX-License-Identifier: GPL-2.0-only
/*
* vmx_nested_tsc_scaling_test
*
* Copyright 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* 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"
/* 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();
}
int main(int argc, char *argv[])
{
struct kvm_vcpu *vcpu;
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;
TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_VMX));
TEST_REQUIRE(kvm_has_cap(KVM_CAP_TSC_CONTROL));
TEST_REQUIRE(sys_clocksource_is_based_on_tsc());
/*
* 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_with_one_vcpu(&vcpu, l1_guest_code);
vcpu_alloc_vmx(vm, &vmx_pages_gva);
vcpu_args_set(vcpu, 1, vmx_pages_gva);
tsc_khz = __vcpu_ioctl(vcpu, 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(vcpu, KVM_SET_TSC_KHZ, (void *) (tsc_khz / l1_scale_factor));
for (;;) {
struct ucall uc;
vcpu_run(vcpu);
TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
switch (get_ucall(vcpu, &uc)) {
case UCALL_ABORT:
REPORT_GUEST_ASSERT(uc);
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;
}
Codebase Browser
linux