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

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Message-ID: <aXAjMxbeMO0pioNF@google.com>
Date: Tue, 20 Jan 2026 16:52:03 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: bp@...en8.de, chao.gao@...el.com, dave.hansen@...el.com, 
	isaku.yamahata@...el.com, kai.huang@...el.com, kas@...nel.org, 
	kvm@...r.kernel.org, linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	mingo@...hat.com, pbonzini@...hat.com, tglx@...utronix.de, 
	vannapurve@...gle.com, x86@...nel.org, yan.y.zhao@...el.com, 
	xiaoyao.li@...el.com, binbin.wu@...el.com
Subject: Re: [PATCH v4 12/16] x86/virt/tdx: Add helpers to allow for
 pre-allocating pages

On Thu, Nov 20, 2025, Rick Edgecombe 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;

The caller passed in number of pages to be added as @cnt, don't hardcode what
could be conflicting information.  If the caller wants to add 50 pages, then this
code damn well needs to prepare for adding 50 pages, not 5.