linux-kernel - Re: [PATCH v2 06/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX TD creation

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Message-ID: <426b1b42-0803-4c44-b101-78c46341df24@intel.com>
Date: Tue, 12 Nov 2024 13:40:26 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "pbonzini@...hat.com" <pbonzini@...hat.com>,
 "seanjc@...gle.com" <seanjc@...gle.com>
Cc: "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
 "Yao, Yuan" <yuan.yao@...el.com>, "Huang, Kai" <kai.huang@...el.com>,
 "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>,
 "Li, Xiaoyao" <xiaoyao.li@...el.com>,
 "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "tony.lindgren@...ux.intel.com" <tony.lindgren@...ux.intel.com>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "Zhao, Yan Y" <yan.y.zhao@...el.com>,
 "Chatre, Reinette" <reinette.chatre@...el.com>,
 "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v2 06/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX TD
 creation

On 11/12/24 13:21, Edgecombe, Rick P wrote:
> On Tue, 2024-11-12 at 12:17 -0800, Dave Hansen wrote:
>> On 10/30/24 12:00, Rick Edgecombe wrote:
>>> +u64 tdh_mng_create(u64 tdr, u64 hkid)
>>> +{
>>> +   struct tdx_module_args args = {
>>> +           .rcx = tdr,
>>> +           .rdx = hkid,
>>> +   };
>>> +   clflush_cache_range(__va(tdr), PAGE_SIZE);
>>> +   return seamcall(TDH_MNG_CREATE, &args);
>>> +}
>>> +EXPORT_SYMBOL_GPL(tdh_mng_create);
>> I'd _prefer_ that this explain why the clflush is there.
> How about:
> /*
>  * The TDX module exposes a CLFLUSH_BEFORE_ALLOC bit to specify whether
>  * a CLFLUSH of pages is required before handing them to the TDX module.
>  * Be conservative and make the code simpler by doing the CLFLUSH
>  * unconditionally.
>  */

Is there a chance we could put this in a helper so the "be conservative"
policy is centralized in one location?  The comment could also go there.