[PATCH v2 0/3] x86/cpuid: KVM: TDX CPUID fixes

[Sean Christopherson <seanjc@google.com>]

Boris or Dave, can you grab patch 1 for 7.4, ideally sooner than later?  That
would avoid having to carry a stable topic branch for a trivial change.

Annotate CPUID entries that have a significant index when reporting TDX
capabilities to userspace, and enforce that userspace honors significant
indices to avoid creating a misconfiguring between KVM and the TDX Module,
which in the worst case scenario could lead to host state getting clobbered.

Patch 1 is a fix to mark function 0x23 as being indexed.  That change is
needed to avoid tripping a WARN sanity check that KVM and the TDX Module
agree on which functions are indexed.

I'd like to take this through the KVM tree as it seems extremely unlikely
the cpuid_function_is_indexed() will conflict or grow other dependencies,
i.e. creating a shared topic branch for this seems rather silly.  Actually,
a better alternative would be to rush patch 1 into 7.4 so that I can use
7.4-rc2 as a base (even rc3 or rc4 would be a-ok).  /me adds an intro

Note, SIGNIFCANT_INDEX isn't a typo, KVM's uAPI macro is misspelled...

v2:
 - Add CPUID.0x23 to the indexed set. [Rick, Binbin]
 - Document that zeroing the index when it's supposed to be ignored is KVM
   ABI that at least QEMU relies on. [Binbin]
 - Zero out all of flags to ensure garbage isn't reported to userspace.

v1: https://lore.kernel.org/all/20260223214336.722463-1-changyuanl@google.com

Changyuan Lyu (1):
  KVM: TDX: Set SIGNIFCANT_INDEX flag as appropriate when filling CPUID
    entries

Sean Christopherson (2):
  x86/cpuid: Mark CPUID function 0x23 as being indexed
  KVM: TDX: Reject KVM_TDX_INIT_VM if indexed CPUID functions don't
    match

 arch/x86/include/asm/cpuid/api.h |  1 +
 arch/x86/kvm/vmx/tdx.c           | 22 +++++++++++++++++++---
 2 files changed, 20 insertions(+), 3 deletions(-)


base-commit: 814607cd40df80d5727957adaa857e0feca43497
-- 
2.56.0.257.gf7497c7d27-goog