Re: [RFC PATCH v2 08/23] KVM: x86/tdp_mmu: Alloc external_spt page for mirror page table splitting

[Huang, Kai]

On Thu, 2025-08-07 at 17:43 +0800, Yan Zhao wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> 
> Enhance tdp_mmu_alloc_sp_split() to allocate a page for sp->external_spt,
	  ^
	  tdp_mmu_alloc_sp_for_split()


[...]

> +static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(bool mirror);
> +

It doesn't seem you need such declaration in _this_ patch.  If any later
patch needs it, then perhaps it's better to do in that patch.

>  static void tdp_account_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)
>  {
>  	kvm_account_pgtable_pages((void *)sp->spt, +1);
> @@ -1475,7 +1477,7 @@ bool kvm_tdp_mmu_wrprot_slot(struct kvm *kvm,
>  	return spte_set;
>  }
>  
> -static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(void)
> +static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(bool mirror)
>  {
>  	struct kvm_mmu_page *sp;
>  
> @@ -1489,6 +1491,15 @@ static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(void)
>  		return NULL;
>  	}
>  
> +	if (mirror) {
> +		sp->external_spt = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
> +		if (!sp->external_spt) {
> +			free_page((unsigned long)sp->spt);
> +			kmem_cache_free(mmu_page_header_cache, sp);
> +			return NULL;
> +		}
> +	}
> +
>  	return sp;
>  }
>  
> @@ -1568,7 +1579,7 @@ static int tdp_mmu_split_huge_pages_root(struct kvm *kvm,
>  			else
>  				write_unlock(&kvm->mmu_lock);
>  
> -			sp = tdp_mmu_alloc_sp_for_split();
> +			sp = tdp_mmu_alloc_sp_for_split(is_mirror_sp(root));
>  
>  			if (shared)
>  				read_lock(&kvm->mmu_lock);