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

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Message-ID: <9dcaa60c-6ffa-4f94-b002-3510110782dd@linux.intel.com>
Date: Thu, 27 Nov 2025 10:38:35 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
 "Huang, Kai" <kai.huang@...el.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>,
 "Hansen, Dave" <dave.hansen@...el.com>, "Zhao, Yan Y"
 <yan.y.zhao@...el.com>, "Wu, Binbin" <binbin.wu@...el.com>,
 "kas@...nel.org" <kas@...nel.org>, "seanjc@...gle.com" <seanjc@...gle.com>,
 "mingo@...hat.com" <mingo@...hat.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "pbonzini@...hat.com" <pbonzini@...hat.com>,
 "Yamahata, Isaku" <isaku.yamahata@...el.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>,
 "Annapurve, Vishal" <vannapurve@...gle.com>, "Gao, Chao"
 <chao.gao@...el.com>, "bp@...en8.de" <bp@...en8.de>,
 "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v4 12/16] x86/virt/tdx: Add helpers to allow for
 pre-allocating pages



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.