Re: [PATCH] KVM: x86/mmu: Implement memslot deletion for TDX

[Sean Christopherson]

On Thu, Jun 20, 2024, Rick Edgecombe wrote:
> Force TDX VMs to use the KVM_X86_QUIRK_SLOT_ZAP_ALL behavior.
> 
> TDs cannot use the fast zapping operation to implement memslot deletion for
> a couple reasons:
> 1. KVM cannot zap TDX private PTEs and re-fault them without coordinating

Uber nit, this isn't strictly true, for KVM's definition of "zap" (which is fuzzy
and overloaded).  KVM _could_ zap and re-fault *leaf* PTEs, e.g. BLOCK+UNBLOCK.
It's specifically the full teardown and rebuild of the "fast zap" that doesn't
play nice, as the non-leaf S-EPT entries *must* be preserved due to how the TDX
module does is refcounting.