Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:
> On 18/03/21 15:52, Vitaly Kuznetsov wrote:
>> Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:
>>
>>> On 18/03/21 15:09, Vitaly Kuznetsov wrote:
>>>> +static inline void check_tsc_msr_tsc_page(struct ms_hyperv_tsc_page *tsc_page)
>>>> +{
>>>> + u64 r1, r2, t1, t2;
>>>> + s64 delta_ns;
>>>> +
>>>> + /* 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);
>>>> + 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;
>>>> +
>>>> + /* 1% tolerance */
>>>> + GUEST_ASSERT(delta_ns * 100 < (t2 - t1) * 100);
>>>> +}
>>>> +
>>>
>>> I think you should also be able to check r1 and r2 individually, not
>>> just r1 and r2. Is that correct?
>>
>> Right, we could've checked r1 == t1 and r2 == t2 actually (with some
>> tiny margin of course). Let me try that.
>
> np, I can do that too. Just checking my recollection of the TLFS.
>
I already hacked it, patch attached :-) Feel free to squash it or put
your own version in.
--
Vitaly
>From dae56d5d5c5fc7442d4dabf96a9c322acb42f458 Mon Sep 17 00:00:00 2001
From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
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 <vkuznets@xxxxxxxxxx>
---
.../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
