[PATCH v9 00/21] KVM: x86: Cleaning up the KVM clock mess, part 1

[Sean Christopherson <seanjc@google.com>]

Part 1 of David's series to clean up the host-side mess of kvmclock.  The cut
point in this version is still quite arbitrary, but what's left for "part 2" 
fits nicely into 2-3 buckets:

  1: Masterclock overhaul
  2. New uAPI and tests

As mentioned elsewhere, my plan is to throw this into an unstable topic branch
asap so it can be used as a base for part 2, but will target 7.4, not 7.3.  I
won't publish it to kvm-x86/next until 7.3-rc1, to avoid polluting linux-next,
and I'll rebase the whole thing on one of 7.3-rc1, 7.3-rc2, or an updated
kvm/next.

v9:
 - Pull in "Compute kvmclock base without pvclock_gtod_data" before "Avoid NTP
   frequency skew for KVM clock on 32-bit host" to avoid having to provide what
   is effectively an open-coded version of ktime_mono_to_any() to avoid data
   races. [Sashiko].
 - Pull in use of kernel timekeeping snapshots, split in three patches purely
   to aid review and bisection.
 - Check and clear KVM_REQ_MASTERCLOCK_UPDATE in kvm_arch_vcpu_postcreate().
   [me, Sashiko]
 - Add the missing return value in "Move "no master clock" fallback from...".
   [Sashiko]

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@infradead.org

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              | 491 +++++++++++++++-----------------
 arch/x86/kvm/x86.h              |   3 +-
 7 files changed, 245 insertions(+), 272 deletions(-)


base-commit: 1b731e5ded480bd1e5546aed35584238661ce72e
-- 
2.55.0.679.g6767b8d81c-goog