Re: [PATCH v7 00/36] Cleaning up the KVM clock mess

[Sean Christopherson <seanjc@xxxxxxxxxx>]

On Tue, Jul 28, 2026, David Woodhouse wrote:
> This is v7 of the series to clean up the KVM clock, rebased onto
> kvm-x86/next (patch 1 of v6 is already merged there as commit
> 710b3a30f407).

FYI, I'm going to rebase that commit again, to put all of this in a dedicated
topic branch.  But I'll also take care of updating references in commit 
messages.
More below.

> David Woodhouse (33):
>       KVM: x86: Improve accuracy of KVM clock when TSC scaling is in force
>       KVM: x86: Explicitly disable TSC scaling without CONSTANT_TSC
>       KVM: x86: Activate master clock immediately on vCPU creation
>       KVM: x86: Avoid NTP frequency skew for KVM clock on 32-bit host
>       KVM: x86: Fold __get_kvmclock() into get_kvmclock()
>       KVM: x86: Drop CPU pinning in get_kvmclock()
>       KVM: x86: Restructure get_kvmclock()
>       KVM: x86: Fix KVM clock precision in get_kvmclock() with TSC scaling
>       KVM: x86: Use get_kvmclock() in kvm_get_wall_clock_epoch()
>       KVM: x86: Fix compute_guest_tsc() to handle negative time deltas
>       KVM: x86: Restructure kvm_guest_time_update() for TSC upscaling
>       KVM: x86: Simplify and comment kvm_get_time_scale()

I'll post a new version up through here, get it applied soon-ish, and then get
back to chipping away at the rest of the series.  It'd obviously be nice to get
all the cleanups (and the tests) into 7.3, but I suspect the rest will take a
bit of back and worth (with Sashiko, if not me :-D).

I may punt on "Restructure kvm_guest_time_update() for TSC upscaling" if I have
trouble sorting through Sashiko's feedback, but I'll give it a shot.  I need to
page that all back in anyways.

>       KVM: x86: Remove implicit rdtsc() from kvm_compute_l1_tsc_offset()
>       KVM: x86: Improve synchronization in kvm_synchronize_tsc()
>       KVM: x86: Kill last_tsc_{nsec,write,offset} fields
>       KVM: x86: Replace nr_vcpus_matched_tsc count with all_vcpus_matched_tsc 
> bool
>       KVM: x86: Allow KVM master clock mode when TSCs are offset from each 
> other
>       KVM: x86: Factor out kvm_use_master_clock()
>       KVM: x86: Avoid gratuitous global clock updates
>       KVM: x86/xen: Prevent runstate times from becoming negative
>       KVM: x86: Avoid redundant masterclock updates from multiple vCPUs
>       KVM: x86: Remove runtime Xen TSC frequency CPUID update
>       KVM: x86: Re-synchronize TSC after KVM_SET_TSC_KHZ
>       KVM: x86: Use ktime_get_snapshot_id() for master clock
>       KVM: x86: Compute kvmclock base without pvclock_gtod_data
>       KVM: x86: Cache host vclock_mode for masterclock eligibility checks
>       KVM: x86: Remove pvclock_gtod_data and private timekeeping code
>       KVM: x86: Activate master clock from kvm_arch_init_vm()
>       KVM: selftests: Use UAPI pvclock-abi.h in xen_shinfo_test
>       KVM: x86: Add KVM_VCPU_TSC_SCALE and fix the documentation on TSC 
> migration
>       KVM: selftests: Add master clock offset test
>       KVM: selftests: Add Xen/generic CPUID timing leaf test
>       KVM: selftests: Add Xen runstate migration test
> 
> Jack Allister (3):
>       UAPI: x86: Move pvclock-abi to UAPI for x86 platforms
>       KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for accurate KVM clock migration
>       KVM: selftests: Add KVM/PV clock selftest to prove timer correction