linux-kernel - Re: [PATCH v4 07/16] x86/virt/tdx: Add tdx_alloc/free

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Message-ID: <474f5ace-e237-4c01-b0bc-d3e68ecc937b@intel.com>
Date: Wed, 3 Dec 2025 10:21:37 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "nik.borisov@...e.com" <nik.borisov@...e.com>,
 "kas@...nel.org" <kas@...nel.org>
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>,
 "Zhao, Yan Y" <yan.y.zhao@...el.com>, "Wu, Binbin" <binbin.wu@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "seanjc@...gle.com" <seanjc@...gle.com>, "mingo@...hat.com"
 <mingo@...hat.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>,
 "Yamahata, Isaku" <isaku.yamahata@...el.com>,
 "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 07/16] x86/virt/tdx: Add tdx_alloc/free_page() helpers

On 12/3/25 10:15, Edgecombe, Rick P wrote:
> On Wed, 2025-12-03 at 07:41 -0800, Dave Hansen wrote:
>> It's fixed at a "page pair" in the ABI documentation, no?
>>
>> If Intel wants anything else, it should have documented that as the ABI.
>> So, as far as the code goes, it's a "page pair" now and forever. Linux
>> does not need to go out of its way to make it inflexible, but there's no
>> need to add complexity now for some future that may never come.
>>
>> I agree with Nikolay: KISS.
> Thanks Dave. Yes, let's stick to the spec. I'm going to try to pull the loops
> out too because we can get rid of the union array thing too.

Also, I honestly don't see the problem with just allocating an order-1
page for this. Yeah, the TDX modules doesn't need physically contiguous
pages, but it's easier for _us_ to lug them around if they are
physically contiguous.

Plus, if you permanently allocate 2 order-0 pages, you are _probably_
going to permanently destroy 2 potential future 2MB pages. The order-1
allocation will only destroy 1.