Re: [PATCH 08/17] KVM: TDX: Drop kvm_x86_ops.link_external_spt(), use .set_external_spte() for all

Yan Zhao
2026-03-30T07:08:06Z

On Fri, Mar 27, 2026 at 01:14:12PM -0700, Rick Edgecombe wrote:
> From: Sean Christopherson <seanjc@google.com>
>
> Drop the dedicated .link_external_spt() for linking non-leaf S-EPT pages,
> and instead funnel everything through .set_external_spte(). 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 settings 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's just wouldn't be a net
"it's" --> "it".

> positive.