[PATCH v3 2/2] selftests: kvm: Check that TSC page value is small after KVM_SET_CLOCK(0)

[Vitaly Kuznetsov]

Add a test for the issue when KVM_SET_CLOCK(0) call could cause
TSC page value to go very big because of a signedness issue around
hv_clock->system_time.

Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
---
 tools/testing/selftests/kvm/x86_64/hyperv_clock.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86_64/hyperv_clock.c 
b/tools/testing/selftests/kvm/x86_64/hyperv_clock.c
index ffbc4555c6e2..7f1d2765572c 100644
--- a/tools/testing/selftests/kvm/x86_64/hyperv_clock.c
+++ b/tools/testing/selftests/kvm/x86_64/hyperv_clock.c
@@ -80,19 +80,24 @@ static inline void check_tsc_msr_rdtsc(void)
        GUEST_ASSERT(delta_ns * 100 < (t2 - t1) * 100);
 }
 
+static inline u64 get_tscpage_ts(struct ms_hyperv_tsc_page *tsc_page)
+{
+       return mul_u64_u64_shr64(rdtsc(), tsc_page->tsc_scale) + 
tsc_page->tsc_offset;
+}
+
 static inline void check_tsc_msr_tsc_page(struct ms_hyperv_tsc_page *tsc_page)
 {
        u64 r1, r2, 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;
+       t1 = get_tscpage_ts(tsc_page);
        r1 = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
 
        /* 10 ms tolerance */
        GUEST_ASSERT(r1 >= t1 && r1 - t1 < 100000);
        nop_loop();
 
-       t2 = mul_u64_u64_shr64(rdtsc(), tsc_page->tsc_scale) + 
tsc_page->tsc_offset;
+       t2 = get_tscpage_ts(tsc_page);
        r2 = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
        GUEST_ASSERT(r2 >= t1 && r2 - t2 < 100000);
 }
@@ -130,7 +135,11 @@ static void guest_main(struct ms_hyperv_tsc_page 
*tsc_page, vm_paddr_t tsc_page_
 
        tsc_offset = tsc_page->tsc_offset;
        /* Call KVM_SET_CLOCK from userspace, check that TSC page was updated */
+
        GUEST_SYNC(7);
+       /* Sanity check TSC page timestamp, it should be close to 0 */
+       GUEST_ASSERT(get_tscpage_ts(tsc_page) < 100000);
+
        GUEST_ASSERT(tsc_page->tsc_offset != tsc_offset);
 
        nop_loop();
-- 
2.30.2