[PATCH v4 27/28] KVM: TDX: Bug the VM if extending the initial measurement fails

[Sean Christopherson]

On Tue, Nov 04, 2025, Binbin Wu wrote:
> 
> 
> On 10/31/2025 4:09 AM, Sean Christopherson wrote:
> > WARN and terminate the VM if TDH_MR_EXTEND fails, as extending the
> > measurement should fail if and only if there is a KVM bug, or if the S-EPT
> > mapping is invalid.  Now that KVM makes all state transitions mutually
> > exclusive via tdx_vm_state_guard, it should be impossible for S-EPT
> > mappings to be removed between kvm_tdp_mmu_map_private_pfn() and
> > tdh_mr_extend().
> > 
> > Holding slots_lock prevents zaps due to memslot updates,
> > filemap_invalidate_lock() prevents zaps due to guest_memfd PUNCH_HOLE,
> > vcpu->mutex locks prevents updates from other vCPUs, kvm->lock prevents
> > VM-scoped ioctls from creating havoc (e.g. by creating new vCPUs), and all
> > usage of kvm_zap_gfn_range() is mutually exclusive with S-EPT entries that
> > can be used for the initial image.
> > 
> > For kvm_zap_gfn_range(), the call from sev.c is obviously mutually
> > exclusive, TDX disallows KVM_X86_QUIRK_IGNORE_GUEST_PAT so the same goes
> > for kvm_noncoherent_dma_assignment_start_or_stop(), and
> > __kvm_set_or_clear_apicv_inhibit() is blocked by virtue of holding all
> > VM and vCPU mutexes (and the APIC page has its own non-guest_memfd memslot
> 
> Nit:
> It sounds like TDX is using the memslot for the APIC page, but for a TD, the
> memslot for the APIC page is never initialized or used?

Oh!  Good point.  I'll tweak that snippet when applying.