[PATCH v3 00/21] KVM: x86: Fix nested TSC scaling edge cases

[Sean Christopherson <seanjc@google.com>]

Amirmohammad's fix to saturate L2's TSC frequency when stacking scale up/down
ratios across L1+L2 yields a final scaling ratio that can't be plugged into
hardware.  The actual fix is functionally the same as v2, but I rewrote the
comments and changelog to try and make them more approachable to KVM developers
(AI has a habit of generating extremely verbose, "mathy" descriptions of bugs
and fixes).

Patch 2 fixes a flaw pointed out by Sashiko.

Patch 3 fixes an off-by-one issue in KVM_SET_TSC_KHZ that is a complete
non-issue in practice, but confused the heck out of me and made writing the
testcases unnecessarily annoying.

The rest of the pile extends and cleans up the nested TSC scaling test to
validate the saturation fixes, and to test all four combinations of scaling
L1+L2 up+down (the existing code testing only L1 down, L2 up).

v2: https://lore.kernel.org/all/20260723182159.2320033-1-amirmohammad.eftekhar@cispa.de

Amirmohammad Eftekhar (1):
  KVM: x86: Saturate L2's TSC frequency if it exceeds hardware supports

Sean Christopherson (20):
  KVM: SVM: Fallback to the default TSC ratio if KVM tries to use a bad
    multiplier
  KVM: x86: Allow userspace to set KVM's max supported guest TSC
    frequency
  KVM: selftests: Use KVM's pRNG to randomize L1's TSC ratio in TSC
    scaling test
  KVM: selftests: Drop redundant VMWRITE of TSC_MULTIPLIER_HIGH
  KVM: selftests: Drop unnecessary use of PRIu64 in nested TSC scaling
    test
  KVM: selftests: Randomize L2's scale factor in nested TSC scaling test
  KVM: selftests: Rename TSC freq checkers in nested TSC scaling test
  KVM: selftests: Extract guts of nested TSC scaling test to helper
    function
  KVM: selftests: Track L2 multiplier, not scale-up factor, in nested
    TSC test
  KVM: selftests: Print out the failing L{0,1,2} level in nested TSC
    scaling test
  KVM: selftests: Allow +/- 1 tolerance if expected TSC frequency is
    <100
  KVM: selftests: Use KVM's reported TSC KHz as L0's frequency (sanity
    checked)
  KVM: selftests: Explicitly pass TSC frequencies to guts of TSC scaling
    test
  KVM: selftests: Sanity check KVM's default TSC freq in nested TSC
    scaling test
  KVM: selftests: Test L1 "up" and L2 "down" in nested TSC scaling test
  KVM: selftests: Verify that KVM saturates L2 TSC freq on
    {under,over}flow
  KVM: selftests: Test non-zero TSC offset on SVM in nested TSC scaling
    test
  KVM: selftests: Randomize L2's TSC offset in the nested TSC scaling
    test
  KVM: selftests: Use GUEST_SYNC2() in nested TSC scaling test
  KVM: selftests: Spell out UCALL in nested TSC scaling test's enums

 arch/x86/kvm/svm/svm.c                        |   9 +
 arch/x86/kvm/x86.c                            |  62 ++++-
 .../kvm/x86/nested_tsc_scaling_test.c         | 232 +++++++++++-------
 3 files changed, 209 insertions(+), 94 deletions(-)


base-commit: b378201ccd5280d0fff89bbe55e1eb00620ec0d5
-- 
2.56.0.rc1.315.gc6ed9934b7-goog