From dae56d5d5c5fc7442d4dabf96a9c322acb42f458 Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Thu, 18 Mar 2021 16:21:18 +0100 Subject: [PATCH] selftests: KVM: hyper-v: check_tsc_msr_tsc_page() fix. Signed-off-by: Vitaly Kuznetsov --- .../selftests/kvm/x86_64/hyperv_clock.c | 25 ++++++++++--------- 1 file changed, 13 insertions(+), 12 deletions(-) diff --git a/tools/testing/selftests/kvm/x86_64/hyperv_clock.c b/tools/testing/selftests/kvm/x86_64/hyperv_clock.c index 39d6491d8458..aacb6d2697da 100644 --- a/tools/testing/selftests/kvm/x86_64/hyperv_clock.c +++ b/tools/testing/selftests/kvm/x86_64/hyperv_clock.c @@ -82,22 +82,23 @@ static inline void check_tsc_msr_rdtsc(void) static inline void check_tsc_msr_tsc_page(struct ms_hyperv_tsc_page *tsc_page) { - u64 r1, r2, t1, t2; - s64 delta_ns; + u64 t1, t2; - /* Compare TSC page clocksource with HV_X64_MSR_TIME_REF_COUNT */ - t1 = mul_u64_u64_shr64(rdtsc(), tsc_page->tsc_scale) + tsc_page->tsc_offset; - r1 = rdmsr(HV_X64_MSR_TIME_REF_COUNT); + /* + * Make TSC run for a while to make sure clocksources don't diverge + * over time. + */ nop_loop(); - t2 = mul_u64_u64_shr64(rdtsc(), tsc_page->tsc_scale) + tsc_page->tsc_offset; - r2 = rdmsr(HV_X64_MSR_TIME_REF_COUNT); - delta_ns = ((r2 - r1) - (t2 - t1)) * 100; - if (delta_ns < 0) - delta_ns = -delta_ns; + /* + * Get readings from TSC page and Reference TSC clocksources and make + * sure they match. + */ + t1 = mul_u64_u64_shr64(rdtsc(), tsc_page->tsc_scale) + tsc_page->tsc_offset; + t2 = rdmsr(HV_X64_MSR_TIME_REF_COUNT); - /* 1% tolerance */ - GUEST_ASSERT(delta_ns * 100 < (t2 - t1) * 100); + /* 10us tolerance */ + GUEST_ASSERT(t2 - t1 <= 100); } static void guest_main(struct ms_hyperv_tsc_page *tsc_page, vm_paddr_t tsc_page_gpa) -- 2.30.2