[PATCH v6 00/12] KVM: x86: Bus Lock Detect fixes and SVM support

[Sean Christopherson <seanjc@google.com>]

Fix KVM's handling of DR6.BLD, and add support for virtualizing BLD on SVM.
KUT tests: https://lore.kernel.org/all/20260925230003.2362261-1-seanjc@google.com

v6:
 - Throw in the towel, at least for now, on WARNing if KVM sees a DR6 without
   all of the fixed-1 bits set. [Sashiko]

v5:
 - https://lore.kernel.org/all/20260930011313.3197688-1-seanjc@google.com
 - Fix the DR6.BLD clobbering bug Sashiko pointed out. [Sashiko]
 - Force-set fixed-1 bits after synchronizing DR6 from the guest (because the
   guest could set bits that are supposed to be fixed-1 due to virtualization
   holes).
 - Open code nested_vmcb12_has_lbrv().
 - Fix the Author for Ravi's patch.
 - Add svm_need_lbr_virtualization() to preserve short-circuit logic.
 - Rename kvm_dr6_fixed() to kvm_get_dr6_fixed_1().
 - Invert svm_get_debugctl_reserved_bits() into svm_get_supported_debugctl()
   to match VMX, and KVM's preferred style.

v4:
 * Rename nested_vmcb12_has_lbrv() to nested_lbrv_enabled() (Yosry).
 * Drop the redundant !lbrv check and the extra comment (Yosry).
 * Spell out in the changelog what breaks when DR6_BUS_LOCK is forced to 1
   (Nikunj).
 * Make it a pure NFC macro-to-helper conversion, and move the
   BUS_LOCK_DETECT gating to patch 5 (Nikunj).
 * Fold in the DEBUGCTLMSR_BUS_LOCK_DETECT gating moved from patch 4.
 * Collect Reviewed-by tags.

v3:
 * https://lore.kernel.org/kvm/20260709082953.69434-1-shivansh.dhiman@amd.com
 * Reworked the single v2 patch into a prep series (patches 1-4) plus the
   feature.
 * Rewrite svm_update_lbrv() as 'if' statements so the BLD LBRV
   dependency can be added cleanly (Yosry Ahmed).
 * Sanitize V_LBR in the nested control cache like NP/GMET and drop the
   redundant X86_FEATURE_LBRV checks (Yosry Ahmed).
 * Use kvm_dr6_fixed() for nested DR6 instead of DR6_FIXED_1 | DR6_RTM.
 * Compute DEBUGCTL reserved bits per-vCPU, gating BUS_LOCK_DETECT on
   guest CPUID rather than a static macro.

v2:
 * https://lore.kernel.org/kvm/20260629081018.60618-1-shivansh.dhiman@amd.com
 * Rebased on kvm-x86-next-2026.06.24.
 * Used guest_cpu_cap_has() instead of guest_cpuid_has().

v1: https://lore.kernel.org/all/20240808062937.1149-5-ravi.bangoria@amd.com

Ravi Bangoria (1):
  KVM: SVM: Add support for virtualizating Bus Lock Detect

Sean Christopherson (8):
  KVM: x86: Preserve DR6.BLD (Bus Lock Detect) when delivering #DB
    payload
  KVM: x86: Rename kvm_dr6_fixed() => kvm_get_dr6_fixed_1()
  KVM: Return an "unsigned long", not "u64" for the fixed-1 DR6 bits
  KVM: x86: Force fixed-1 bits in DR6 after synchronizing with hardware
  KVM: x86: Set guest's fixed-1 DR6 bits when delivering #DB payload
  KVM: x86: Kill off DR6_FIXED_1 to prevent future misuse
  KVM: SVM: Add helper to query if LBR virtualization needs to be
    enabled
  KVM: nSVM: Open code check on LBR virtualization being enabled in
    vmcb12

Shivansh Dhiman (3):
  KVM: nSVM: Disable LBRV in nested control cache when unsupported
  KVM: nSVM: Don't assume all active-low bits DR6 are fixed-1
  KVM: SVM: Add a vCPU-aware helper to get supported DEBUGCTL bits

 arch/x86/kvm/regs.c       |  8 +++---
 arch/x86/kvm/regs.h       | 11 ++++----
 arch/x86/kvm/svm/nested.c | 27 +++++++++-----------
 arch/x86/kvm/svm/svm.c    | 31 +++++++++++++++++------
 arch/x86/kvm/svm/svm.h    | 12 +++++++--
 arch/x86/kvm/x86.c        | 53 +++++++++++++++++++++++----------------
 6 files changed, 87 insertions(+), 55 deletions(-)


base-commit: 7f734412a73e910658dc81ba74f76af789202f58
-- 
2.56.0.rc1.315.gc6ed9934b7-goog