[v3,0/4] KVM: x86: Introduce quirk KVM_X86_QUIRK_IGNORE_GUEST_PAT

Message

Paolo Bonzini March 4, 2025, 6:06 a.m. UTC

This series is my evolution of Yan's patches at
https://patchew.org/linux/[e-mail]/.

The implementation of the quirk is unchanged, but the concepts in kvm_caps
are a bit different.  In particular:

- if a quirk is not applicable to some hardware, it is still included
  in KVM_CAP_DISABLE_QUIRKS2.  This way userspace knows that KVM is
  *aware* of a particular issue - even if disabling it has no effect
  because the quirk is not a problem on a specific hardware, userspace
  may want to know that it can rely on the problematic behavior not
  being present.  Therefore, KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT is
  simply auto-disabled on TDX machines.

- if instead a quirk cannot be disabled due to limitations, for example
  KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT if self-snoop is not present on
  the CPU, the quirk is removed completely from kvm_caps.supported_quirks
  and therefore from KVM_CAP_DISABLE_QUIRKS2.

This series does not introduce a way to query always-disabled quirks,
which could be for example KVM_CAP_DISABLED_QUIRKS.  This could be
added if we wanted for example to get rid of hypercall patching; it's
a trivial addition.

The main semantic change with respect to v2 is to prevent re-enabling
quirks that have been disabled with KVM_ENABLE_CAP.  This in turn makes
it possible to just use kvm->arch.disabled_quirks for TDX-enabled

Paolo

Supersedes: <[e-mail]>

Paolo Bonzini (3):
  KVM: x86: do not allow re-enabling quirks
  KVM: x86: Allow vendor code to disable quirks
  KVM: x86: remove shadow_memtype_mask

Yan Zhao (3):
  KVM: x86: Introduce supported_quirks to block disabling quirks
  KVM: x86: Introduce Intel specific quirk
    KVM_X86_QUIRK_IGNORE_GUEST_PAT
  KVM: TDX: Always honor guest PAT on TDX enabled guests

 Documentation/virt/kvm/api.rst  | 22 +++++++++++++++++
 arch/x86/include/asm/kvm_host.h |  7 +++++-
 arch/x86/include/uapi/asm/kvm.h |  1 +
 arch/x86/kvm/mmu.h              |  2 +-
 arch/x86/kvm/mmu/mmu.c          | 13 ----------
 arch/x86/kvm/mmu/spte.c         | 19 ++-------------
 arch/x86/kvm/mmu/spte.h         |  1 -
 arch/x86/kvm/svm/svm.c          |  1 +
 arch/x86/kvm/vmx/tdx.c          |  6 +++++
 arch/x86/kvm/vmx/vmx.c          | 43 +++++++++++++++++++++++++++------
 arch/x86/kvm/x86.c              | 13 +++++++---
 arch/x86/kvm/x86.h              |  3 +++
 12 files changed, 87 insertions(+), 44 deletions(-)