Re: [PATCH v4 12/16] x86/virt/tdx: Add helpers to allow for pre-allocating pages

[Binbin Wu]

On 11/27/2025 6:33 AM, Edgecombe, Rick P wrote:
> > >     
> > >     static int tdx_topup_external_fault_cache(struct kvm_vcpu *vcpu, unsigned int cnt)
> > >     {
> > > -	struct vcpu_tdx *tdx = to_tdx(vcpu);
> > > +	struct tdx_prealloc *prealloc = &to_tdx(vcpu)->prealloc;
> > > +	int min_fault_cache_size;
> > >     
> > > -	return kvm_mmu_topup_memory_cache(&tdx->mmu_external_spt_cache, cnt);
> > > +	/* External page tables */
> > > +	min_fault_cache_size = cnt;
> > > +	/* Dynamic PAMT pages (if enabled) */
> > > +	min_fault_cache_size += tdx_dpamt_entry_pages() * PT64_ROOT_MAX_LEVEL;
> > Is the value PT64_ROOT_MAX_LEVEL intended, since dynamic PAMT pages are only
> > needed for 4KB level?
> I'm not sure I follow. We need DPAMT backing for each S-EPT page table.
Oh, right!

IIUIC,  PT64_ROOT_MAX_LEVEL is actually
- PT64_ROOT_MAX_LEVEL - 1 for S-ETP pages since root page is not needed.
- 1 for TD private memory page

It's better to add a comment about it.