[GIT PULL] KVM: x86: Timekeeping fixes+cleanups for 7.4

[Sean Christopherson]

Part 1 of 2 (or maybe 3) of David's war on kvmclock.  Ugh, and when looking at
the shortlog, I realized I botched the author on these:

  KVM: x86: Use kernel timekeeping snapshot for monotonic clock
  KVM: x86: Use kernel timekeeping snapshot to get walltime+TSC

Holler if you would prefer a fixup to get the author right; these have been in
-next for over a month, so I opted to send them as-is instead of doing a super
last minute rewrite.

The following changes since commit d4b7fb647204f0c81dfeae2d1a708e4d858e0c94:

  Merge branch 'kvm-xen-longmode' into HEAD (2026-09-04 17:35:03 +0200)

are available in the Git repository at:

  https://github.com/kvm-x86/linux.git tags/kvm-x86-clocks-7.4

for you to fetch changes up to d7841275e1fb4ad1e1877e56725ebda5b6e3143d:

  KVM: x86: Use kernel timekeeping snapshot to get walltime+TSC (2026-09-11 11:46:19 -0700)

----------------------------------------------------------------
KVM x86 timekeeping fixes and cleanups for 7.4

Fix a variety of warts in KVM's handling of guest TSC, kvmclock, and
timekeeping in general, as a (big) first step towards addressing several
longstanding problems with the kvmclock implementation.

Most notably, fix a precision issue where get_kvmclock_ns() computed the
clock from the *host* TSC without applying guest TSC scaling, causing
systemic drift from the values the guest computes from its own TSC.

As a bonus cleanup, rip out the whole pvclock_gtod_data hack, which was
shadowing the kernel's timekeeping, and use ktime snapshots.

----------------------------------------------------------------
David Woodhouse (14):
      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: Compute kvmclock base without pvclock_gtod_data
      KVM: x86: Avoid NTP frequency skew for KVM clock on 32-bit host
      KVM: x86: Wrap all of __get_kvmclock_master_clock() with CONFIG_X86_64=y
      KVM: x86: Fall back to non-master-clock if clockread fails in 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: Upscale TSC to "now", not master clock when updating PV clocks
      KVM: x86: Simplify and comment kvm_get_time_scale()
      KVM: x86: Remove implicit rdtsc() from kvm_compute_l1_tsc_offset()
      KVM: x86: Use kernel timekeeping snapshots for getting kvmclock time since boot

Sean Christopherson (7):
      KVM: x86: Update "last guest TSC" snapshot prior to enabling IRQs/preemption
      KVM: x86: Drop unnecessary CPU pinning when computing/getting kvmclock
      KVM: x86: Move "no master clock" fallback from __get_kvmclock() to get_kvmclock()
      KVM: x86: Disable preemption, not IRQs, when getting TSC+freq pair
      KVM: x86: Make master clock logic in guest PV clock updates 64-bit only
      KVM: x86: Use kernel timekeeping snapshot for monotonic clock
      KVM: x86: Use kernel timekeeping snapshot to get walltime+TSC

 arch/x86/include/asm/kvm_host.h |   6 +-
 arch/x86/kvm/cpuid.c            |   1 +
 arch/x86/kvm/msrs.c             |   3 +-
 arch/x86/kvm/svm/svm.c          |   3 +-
 arch/x86/kvm/vmx/vmx.c          |  10 +
 arch/x86/kvm/x86.c              | 480 ++++++++++++++++++----------------------
 arch/x86/kvm/x86.h              |   3 +-
 7 files changed, 240 insertions(+), 266 deletions(-)