[v2,00/21] KVM: x86: Add "governed" X86_FEATURE framework

  Add a framework to manage and cache KVM-governed features, i.e. CPUID
based features that require explicit KVM enabling and/or need to be
queried semi-frequently by KVM.  The idea originally came up in the
context of the architectural LBRs series as a way to avoid querying
guest CPUID in hot paths without needing a dedicated flag, but as
evidenced by the shortlog, the most common usage is to handle the ever-
growing list of SVM features that are exposed to L1.

The first six patches are fixes and cleanups related to TSC scaling.
nSVM has WARN_ONs that can be triggered by userspace at will, and the
code is a bit crusty.  They aren't directly related to the governed
stuff, I stumbled upon the issues they fix when staring at the patch to
convert "TSC scaling enabled".  I included them here mainly to avoid
code conflicts.  I'm hoping all of this can go into 6.6, e.g. so that CET
support can build on guest_can_use(), but I can always grab the TSC
patches for 6.6 if the governed stuff needs more time.

Note, I still don't like the name "governed", but no one has suggested
anything else, let alone anything better :-)

v2:
 - Add patches to clean up TSC scaling.
 - Add a comment explaining the virtual VMLOAD/VMLAVE vs. SYSENTER on
   Intel madness.
 - Use a governed feature for X86_FEATURE_VMX.
 - Incorporate KVM capabilities into the main check-and-set helper. [Chao]

v1: https://lore.kernel.org/all/20230217231022.816138-1-seanjc@google.com

Sean Christopherson (21):
  KVM: nSVM: Check instead of asserting on nested TSC scaling support
  KVM: nSVM: Load L1's TSC multiplier based on L1 state, not L2 state
  KVM: nSVM: Use the "outer" helper for writing multiplier to
    MSR_AMD64_TSC_RATIO
  KVM: SVM: Clean up preemption toggling related to MSR_AMD64_TSC_RATIO
  KVM: x86: Always write vCPU's current TSC offset/ratio in vendor hooks
  KVM: nSVM: Skip writes to MSR_AMD64_TSC_RATIO if guest state isn't
    loaded
  KVM: x86: Add a framework for enabling KVM-governed x86 features
  KVM: x86/mmu: Use KVM-governed feature framework to track "GBPAGES
    enabled"
  KVM: VMX: Recompute "XSAVES enabled" only after CPUID update
  KVM: VMX: Check KVM CPU caps, not just VMX MSR support, for XSAVE
    enabling
  KVM: VMX: Rename XSAVES control to follow KVM's preferred "ENABLE_XYZ"
  KVM: x86: Use KVM-governed feature framework to track "XSAVES enabled"
  KVM: nVMX: Use KVM-governed feature framework to track "nested VMX
    enabled"
  KVM: nSVM: Use KVM-governed feature framework to track "NRIPS enabled"
  KVM: nSVM: Use KVM-governed feature framework to track "TSC scaling
    enabled"
  KVM: nSVM: Use KVM-governed feature framework to track "vVM{SAVE,LOAD}
    enabled"
  KVM: nSVM: Use KVM-governed feature framework to track "LBRv enabled"
  KVM: nSVM: Use KVM-governed feature framework to track "Pause Filter
    enabled"
  KVM: nSVM: Use KVM-governed feature framework to track "vGIF enabled"
  KVM: nSVM: Use KVM-governed feature framework to track "vNMI enabled"
  KVM: x86: Disallow guest CPUID lookups when IRQs are disabled

 arch/x86/include/asm/kvm_host.h  | 23 ++++++++-
 arch/x86/include/asm/vmx.h       |  2 +-
 arch/x86/kvm/cpuid.c             | 34 ++++++++++++++
 arch/x86/kvm/cpuid.h             | 46 ++++++++++++++++++
 arch/x86/kvm/governed_features.h | 21 +++++++++
 arch/x86/kvm/mmu/mmu.c           | 20 ++------
 arch/x86/kvm/svm/nested.c        | 57 ++++++++++++----------
 arch/x86/kvm/svm/svm.c           | 81 ++++++++++++++++++--------------
 arch/x86/kvm/svm/svm.h           | 18 ++-----
 arch/x86/kvm/vmx/capabilities.h  |  2 +-
 arch/x86/kvm/vmx/hyperv.c        |  2 +-
 arch/x86/kvm/vmx/nested.c        | 13 ++---
 arch/x86/kvm/vmx/nested.h        |  2 +-
 arch/x86/kvm/vmx/vmx.c           | 81 +++++++++++++++-----------------
 arch/x86/kvm/vmx/vmx.h           |  3 +-
 arch/x86/kvm/x86.c               |  9 ++--
 16 files changed, 261 insertions(+), 153 deletions(-)
 create mode 100644 arch/x86/kvm/governed_features.h


base-commit: fdf0eaf11452d72945af31804e2a1048ee1b574c
  

On Fri, 28 Jul 2023 18:15:47 -0700, Sean Christopherson wrote:
> Add a framework to manage and cache KVM-governed features, i.e. CPUID
> based features that require explicit KVM enabling and/or need to be
> queried semi-frequently by KVM.  The idea originally came up in the
> context of the architectural LBRs series as a way to avoid querying
> guest CPUID in hot paths without needing a dedicated flag, but as
> evidenced by the shortlog, the most common usage is to handle the ever-
> growing list of SVM features that are exposed to L1.
> 
> [...]

Applied to kvm-x86 misc.  I'm still hoping for reviews before sending this on
to Paolo, but I also want to get this into -next sooner than later.  And I
tried to grab everything else for "misc" ahead of time, so hopefully there won't
be much, if any, collateral damage if I need to unwind.

[01/21] KVM: nSVM: Check instead of asserting on nested TSC scaling support
        https://github.com/kvm-x86/linux/commit/06b2c8f7d994
[02/21] KVM: nSVM: Load L1's TSC multiplier based on L1 state, not L2 state
        https://github.com/kvm-x86/linux/commit/3b5ebb78fdc4
[03/21] KVM: nSVM: Use the "outer" helper for writing multiplier to MSR_AMD64_TSC_RATIO
        https://github.com/kvm-x86/linux/commit/b5b10353a0c6
[04/21] KVM: SVM: Clean up preemption toggling related to MSR_AMD64_TSC_RATIO
        https://github.com/kvm-x86/linux/commit/3e6e20a49690
[05/21] KVM: x86: Always write vCPU's current TSC offset/ratio in vendor hooks
        https://github.com/kvm-x86/linux/commit/c1a3910b30f6
[06/21] KVM: nSVM: Skip writes to MSR_AMD64_TSC_RATIO if guest state isn't loaded
        https://github.com/kvm-x86/linux/commit/923428d7f741
[07/21] KVM: x86: Add a framework for enabling KVM-governed x86 features
        https://github.com/kvm-x86/linux/commit/ed425263d977
[08/21] KVM: x86/mmu: Use KVM-governed feature framework to track "GBPAGES enabled"
        https://github.com/kvm-x86/linux/commit/f274417a0920
[09/21] KVM: VMX: Recompute "XSAVES enabled" only after CPUID update
        https://github.com/kvm-x86/linux/commit/73db29bfc576
[10/21] KVM: VMX: Check KVM CPU caps, not just VMX MSR support, for XSAVE enabling
        https://github.com/kvm-x86/linux/commit/82816e485b02
[11/21] KVM: VMX: Rename XSAVES control to follow KVM's preferred "ENABLE_XYZ"
        https://github.com/kvm-x86/linux/commit/080b5890f88e
[12/21] KVM: x86: Use KVM-governed feature framework to track "XSAVES enabled"
        https://github.com/kvm-x86/linux/commit/ae1f7788d4a3
[13/21] KVM: nVMX: Use KVM-governed feature framework to track "nested VMX enabled"
        https://github.com/kvm-x86/linux/commit/d60c21f44fe2
[14/21] KVM: nSVM: Use KVM-governed feature framework to track "NRIPS enabled"
        https://github.com/kvm-x86/linux/commit/f32e9ba4ff57
[15/21] KVM: nSVM: Use KVM-governed feature framework to track "TSC scaling enabled"
        https://github.com/kvm-x86/linux/commit/417293d8eebc
[16/21] KVM: nSVM: Use KVM-governed feature framework to track "vVM{SAVE,LOAD} enabled"
        https://github.com/kvm-x86/linux/commit/a179919b6b08
[17/21] KVM: nSVM: Use KVM-governed feature framework to track "LBRv enabled"
        https://github.com/kvm-x86/linux/commit/2a688180ae59
[18/21] KVM: nSVM: Use KVM-governed feature framework to track "Pause Filter enabled"
        https://github.com/kvm-x86/linux/commit/2b4a6cce48b6
[19/21] KVM: nSVM: Use KVM-governed feature framework to track "vGIF enabled"
        https://github.com/kvm-x86/linux/commit/994e74975227
[20/21] KVM: nSVM: Use KVM-governed feature framework to track "vNMI enabled"
        https://github.com/kvm-x86/linux/commit/17e2299ac6a6
[21/21] KVM: x86: Disallow guest CPUID lookups when IRQs are disabled
        https://github.com/kvm-x86/linux/commit/20b18b1dea4c

--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes