[PATCH v8 00/17] KVM: x86: Cleaning up the KVM clock mess, part 1

[Sean Christopherson]

This is the first half (give or take) of David's series to clean up some of
the mess that is timekeeping in KVM.  The "cut point" is rather arbitrary:
I stopped when I lost confidence in my understanding of the patches.  I'm
planning on diving back into review for the remaining patches asap, but want
to get start landing changes since many of these are fixes.

v8:
 - Obviously cut partway through the full series.
 - Update commit references for 633d7652f80f ("KVM: x86/xen: Do not corrupt
   KVM clock in kvm_xen_shared_info_init()").
 - Chunk the "Restructure ..." patches into individual logical changes
   ("Restructure kvm_guest_time_update() for TSC upscaling" in particular was
   quite gnarly).
 - Ensure the TSC+freq pair during guest time updates happens on a single
   CPU. [Sashiko]
 - Keep __get_kvmclock() as a masterclock-specific helper to avoid deep
   indentation and gotos.
 - Do waaaaay too much spelunking to try piece together the history of some
   of the many warts.
 - Ensure preemption is disabled in get_kvmclock() when getting the TSC freq.

v7: https://lore.kernel.org/all/20260728144954.355376-1-dwmw2@xxxxxxxxxxxxx

David Woodhouse (12):
  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: 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()

Sean Christopherson (5):
  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

 arch/x86/include/asm/kvm_host.h |   6 +-
 arch/x86/kvm/cpuid.c            |   3 +-
 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              | 332 ++++++++++++++++++--------------
 arch/x86/kvm/x86.h              |   3 +-
 7 files changed, 212 insertions(+), 148 deletions(-)


base-commit: 51ba04112e93ac6e04c627eddcea5caf9cbc0134
-- 
2.55.0.571.g244d577d93-goog