linux-kernel - Re: [RFC PATCH v5 16/45] x86/virt/tdx: Add tdx_alloc/free_control

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Message-ID: <4fe6121b-6fe3-4c97-b796-806533ed6806@intel.com>
Date: Tue, 10 Feb 2026 14:19:13 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "seanjc@...gle.com" <seanjc@...gle.com>, "x86@...nel.org" <x86@...nel.org>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 "kas@...nel.org" <kas@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
 "mingo@...hat.com" <mingo@...hat.com>, "tglx@...nel.org" <tglx@...nel.org>,
 "pbonzini@...hat.com" <pbonzini@...hat.com>
Cc: "Huang, Kai" <kai.huang@...el.com>,
 "ackerleytng@...gle.com" <ackerleytng@...gle.com>,
 "sagis@...gle.com" <sagis@...gle.com>,
 "Annapurve, Vishal" <vannapurve@...gle.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "Zhao, Yan Y" <yan.y.zhao@...el.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
 "Yamahata, Isaku" <isaku.yamahata@...el.com>,
 "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>
Subject: Re: [RFC PATCH v5 16/45] x86/virt/tdx: Add
 tdx_alloc/free_control_page() helpers

On 2/10/26 14:15, Edgecombe, Rick P wrote:
> I'm wasn't familiar with atomic_dec_and_lock(). I'm guess the atomic
> part doesn't cover both decrementing *and* taking the lock?

Right. Only 1=>0 is under the lock. All other decs are outside the lock.

It doesn't do the atomic and the lock "atomically together" somehow.