From: David Woodhouse <dwmw2@infradead.org>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Juergen Gross <jgross@suse.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Paul Durrant <paul@xen.org>, Jonathan Cameron <jic23@kernel.org>,
Sascha Bischoff <Sascha.Bischoff@arm.com>,
Marc Zyngier <maz@kernel.org>, Joey Gouly <joey.gouly@arm.com>,
Jack Allister <jalliste@amazon.com>,
Dongli Zhang <dongli.zhang@oracle.com>,
joe.jin@oracle.com, kvm@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
xen-devel@lists.xenproject.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v6 15/36] KVM: x86: Fix compute_guest_tsc() to handle negative time deltas
Date: Sat, 25 Jul 2026 18:11:19 +0100 [thread overview]
Message-ID: <016ebfbfca269245612f246337bb33247a95fdba.camel@infradead.org> (raw)
In-Reply-To: <amPYq48J9TPbmFNl@google.com>
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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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next prev parent reply other threads:[~2026-07-25 17:11 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-03 21:17 [PATCH v6 00/36] Cleaning up the KVM clock mess David Woodhouse
2026-07-03 21:17 ` [PATCH v6 01/36] KVM: x86/xen: Do not corrupt KVM clock in kvm_xen_shared_info_init() David Woodhouse
2026-07-03 21:17 ` [PATCH v6 02/36] KVM: x86: Improve accuracy of KVM clock when TSC scaling is in force David Woodhouse
2026-07-24 21:10 ` Sean Christopherson
2026-07-03 21:17 ` [PATCH v6 03/36] UAPI: x86: Move pvclock-abi to UAPI for x86 platforms David Woodhouse
2026-07-03 21:17 ` [PATCH v6 04/36] KVM: selftests: Use UAPI pvclock-abi.h in xen_shinfo_test David Woodhouse
2026-07-03 21:17 ` [PATCH v6 05/36] KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for accurate KVM clock migration David Woodhouse
2026-07-24 21:17 ` Sean Christopherson
2026-07-25 7:47 ` David Woodhouse
2026-07-28 1:15 ` Sean Christopherson
2026-07-28 2:13 ` David Woodhouse
2026-07-03 21:17 ` [PATCH v6 06/36] KVM: selftests: Add KVM/PV clock selftest to prove timer correction David Woodhouse
2026-07-03 21:17 ` [PATCH v6 07/36] KVM: x86: Explicitly disable TSC scaling without CONSTANT_TSC David Woodhouse
2026-07-03 21:17 ` [PATCH v6 08/36] KVM: x86: Activate master clock immediately on vCPU creation David Woodhouse
2026-07-24 21:19 ` Sean Christopherson
2026-07-25 7:59 ` David Woodhouse
2026-07-25 12:45 ` David Woodhouse
2026-07-03 21:17 ` [PATCH v6 09/36] KVM: x86: Add KVM_VCPU_TSC_SCALE and fix the documentation on TSC migration David Woodhouse
2026-07-03 21:17 ` [PATCH v6 10/36] KVM: x86: Avoid NTP frequency skew for KVM clock on 32-bit host David Woodhouse
2026-07-03 21:17 ` [PATCH v6 11/36] KVM: x86: Fold __get_kvmclock() into get_kvmclock() David Woodhouse
2026-07-03 21:17 ` [PATCH v6 12/36] KVM: x86: Restructure get_kvmclock() David Woodhouse
2026-07-24 21:29 ` Sean Christopherson
2026-07-25 7:53 ` David Woodhouse
2026-07-28 0:49 ` Sean Christopherson
2026-07-03 21:17 ` [PATCH v6 13/36] KVM: x86: Fix KVM clock precision in get_kvmclock() with TSC scaling David Woodhouse
2026-07-03 21:17 ` [PATCH v6 14/36] KVM: x86: Use get_kvmclock() in kvm_get_wall_clock_epoch() David Woodhouse
2026-07-03 21:17 ` [PATCH v6 15/36] KVM: x86: Fix compute_guest_tsc() to handle negative time deltas David Woodhouse
2026-07-24 21:27 ` Sean Christopherson
2026-07-25 7:56 ` David Woodhouse
2026-07-28 0:51 ` Sean Christopherson
2026-07-25 17:11 ` David Woodhouse [this message]
2026-07-03 21:17 ` [PATCH v6 16/36] KVM: x86: Restructure kvm_guest_time_update() for TSC upscaling David Woodhouse
2026-07-03 21:17 ` [PATCH v6 17/36] KVM: x86: Simplify and comment kvm_get_time_scale() David Woodhouse
2026-07-03 21:17 ` [PATCH v6 18/36] KVM: x86: Remove implicit rdtsc() from kvm_compute_l1_tsc_offset() David Woodhouse
2026-07-03 21:17 ` [PATCH v6 19/36] KVM: x86: Improve synchronization in kvm_synchronize_tsc() David Woodhouse
2026-07-03 21:17 ` [PATCH v6 20/36] KVM: x86: Kill last_tsc_{nsec,write,offset} fields David Woodhouse
2026-07-03 21:18 ` [PATCH v6 21/36] KVM: x86: Replace nr_vcpus_matched_tsc count with all_vcpus_matched_tsc bool David Woodhouse
2026-07-03 21:18 ` [PATCH v6 22/36] KVM: x86: Allow KVM master clock mode when TSCs are offset from each other David Woodhouse
2026-07-03 21:18 ` [PATCH v6 23/36] KVM: selftests: Add master clock offset test David Woodhouse
2026-07-03 21:18 ` [PATCH v6 24/36] KVM: x86: Factor out kvm_use_master_clock() David Woodhouse
2026-07-03 21:18 ` [PATCH v6 25/36] KVM: x86: Avoid gratuitous global clock updates David Woodhouse
2026-07-03 21:18 ` [PATCH v6 26/36] KVM: x86/xen: Prevent runstate times from becoming negative David Woodhouse
2026-07-03 21:18 ` [PATCH v6 27/36] KVM: x86: Avoid redundant masterclock updates from multiple vCPUs David Woodhouse
2026-07-03 21:18 ` [PATCH v6 28/36] KVM: x86: Remove runtime Xen TSC frequency CPUID update David Woodhouse
2026-07-03 21:18 ` [PATCH v6 29/36] KVM: selftests: Add Xen/generic CPUID timing leaf test David Woodhouse
2026-07-03 21:18 ` [PATCH v6 30/36] KVM: x86: Re-synchronize TSC after KVM_SET_TSC_KHZ David Woodhouse
2026-07-03 21:18 ` [PATCH v6 31/36] KVM: selftests: Add Xen runstate migration test David Woodhouse
2026-07-26 9:21 ` David Woodhouse
2026-07-03 21:18 ` [PATCH v6 32/36] KVM: x86: Use ktime_get_snapshot_id() for master clock David Woodhouse
2026-07-03 21:18 ` [PATCH v6 33/36] KVM: x86: Compute kvmclock base without pvclock_gtod_data David Woodhouse
2026-07-03 21:18 ` [PATCH v6 34/36] KVM: x86: Cache host vclock_mode for masterclock eligibility checks David Woodhouse
2026-07-03 21:18 ` [PATCH v6 35/36] KVM: x86: Remove pvclock_gtod_data and private timekeeping code David Woodhouse
2026-07-03 21:18 ` [PATCH v6 36/36] KVM: x86: Activate master clock from kvm_arch_init_vm() David Woodhouse
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