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Re: [PATCH v6 15/36] KVM: x86: Fix compute_guest_tsc() to handle negative time deltas
- To: Sean Christopherson <seanjc@xxxxxxxxxx>
- From: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
- Date: Sat, 25 Jul 2026 18:11:19 +0100
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- Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>, Jonathan Corbet <corbet@xxxxxxx>, Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, "H. Peter Anvin" <hpa@xxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Paul Durrant <paul@xxxxxxx>, Jonathan Cameron <jic23@xxxxxxxxxx>, Sascha Bischoff <Sascha.Bischoff@xxxxxxx>, Marc Zyngier <maz@xxxxxxxxxx>, Joey Gouly <joey.gouly@xxxxxxx>, Jack Allister <jalliste@xxxxxxxxxx>, Dongli Zhang <dongli.zhang@xxxxxxxxxx>, joe.jin@xxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kselftest@xxxxxxxxxxxxxxx
- Delivery-date: Sat, 25 Jul 2026 17:12:05 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Fri, 2026-07-24 at 14:27 -0700, Sean Christopherson wrote:
>
> To cut down on the duplicate code, and IMO to make it easier to identify the
> differences, how about this?
>
> s64 delta_ns = kernel_ns - vcpu->arch.this_tsc_nsec;
> u64 tsc;
>
> /* Handle negative deltas gracefully (master clock ref may be earlier)
> */
> tsc = pvclock_scale_delta(abs(-delta_ns),
> vcpu->arch.virtual_tsc_mult,
> vcpu->arch.virtual_tsc_shift);
>
> return vcpu->arch.this_tsc_write + (delta_ns >= 0 ? tsc : -tsc);
Oh, I missed that part. Done, rebased to kvm-x86/next and pushed to my
kvmclock7 branch while I test it and await further feedback.
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