Re: [PATCH v2 01/15] KVM: TDX: Drop kvm_x86_ops.link_external_spt()

[Sean Christopherson <seanjc@google.com>]

On Sat, May 09, 2026, Yan Zhao wrote:
> From: Sean Christopherson <seanjc@google.com>
> 
> Drop the dedicated .link_external_spt() for linking S-EPT pages, and
> instead funnel everything through .set_external_spte() for mapping S-EPT
> entries. Using separate hooks doesn't help prevent TDP MMU details from
> bleeding into TDX, and vice versa; to the contrary, dedicated callbacks
> will result in _more_ pollution when hugepage support is added, e.g. will
> require the TDP MMU to know details about the splitting rules for TDX that
> aren't all that relevant to the TDP MMU.
> 
> Ideally, KVM would provide a single pair of hooks to set S-EPT entries,
> one hook for setting SPTEs under write-lock and another for setting SPTEs
> under read-lock (e.g. to ensure the entire operation is "atomic", to allow
> for failure, etc.).  Sadly, TDX's requirement that all child S-EPT entries
> are removed before the parent makes that impractical: the TDP MMU
> deliberately prunes non-leaf SPTEs and _then_ processes its children, thus
> making it quite important for the TDP MMU to differentiate between zapping
> leaf and non-leaf S-EPT entries.
> 
> However, that's the _only_ case that's truly special, and even that case
> could be shoehorned into a single hook; it just wouldn't be a net positive.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> [Rick: add in trivial feedback]
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
> ---
> MMU_refactors v2:
> - Moved this patch to the very beginning of the series so that when
>   warnings like "KVM_BUG_ON(!is_shadow_present_pte(new_spte), kvm)" are
>   removed from __tdp_mmu_set_spte_atomic() in TDP MMU in a later patch, the
>   atomic zap change can be propagated via the .set_external_spte() op.
>   (Yan).
> 
> MMU_refactors v1:
>  - rename external_spt->sept_pt (Rick, Yan)

Put the versioning info below the "---" that delineates the diff, otherwise
`git am` adds it to the changelog.

> ---

I.e. put it here.

>  arch/x86/include/asm/kvm-x86-ops.h |  1 -
>  arch/x86/include/asm/kvm_host.h    |  3 --
>  arch/x86/kvm/mmu/tdp_mmu.c         | 29 +-------------
>  arch/x86/kvm/vmx/tdx.c             | 63 ++++++++++++++++++++----------
>  4 files changed, 44 insertions(+), 52 deletions(-)