Re: [PATCH v4 08/17] KVM: TDX: Adjust the topup count of DPAMT page pairs for splitting S-EPT

[Edgecombe, Rick P]

On Thu, 2026-10-22 at 15:24 +0800, Yan Zhao wrote:
> static int tdx_topup_external_pamt_cache(struct kvm *kvm, struct kvm_vcpu
> *vcpu,
>                                          bool with_root_spt, int min_nr_spts)
> {
>         struct tdx_pamt_cache *pamt_cache;
>         int dpamt_pairs = min_nr_spts;
> 
>         pamt_cache = tdx_get_pamt_cache(kvm, vcpu);
>         if (!pamt_cache)
>                 return -EIO;
> 
>         /* DPAMT page pair for the root SPT has already been installed */
>         if (with_root_spt)
>                 dpamt_pairs -= 1;
> 
>         /* +1 pair for 4KB guest private page */
>         dpamt_pairs += 1;
> 
>         return tdx_topup_pamt_cache(pamt_cache, dpamt_pairs);
> }

Yes this looks much clearer than even the upstream code. Do you have any better
ideas than "4KB guest private page" though? Because in the split case it is
actually for 512 guest private pages. We should put an artful comment to explain
both cases while not making it look like something that has a better solution.
Because I'm thinking there isn't one.

> 
> In the fault path, mmu_topup_memory_caches() calls:
> r = kvm_x86_call(topup_external_cache)(vcpu->kvm, vcpu, true,
> PT64_ROOT_MAX_LEVEL);
> 
> In the split path, tdp_mmu_alloc_sp_for_split() calls:
> kvm_x86_call(topup_external_cache)(kvm, kvm_get_running_vcpu(), false, 1);