linux-kernel - Re: [RFC PATCH 03/20] x86/virt/seamldr: Introduce a wrapper for P-SEAMLDR SEAMCALLs

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Message-ID: <e969d071-1161-4323-89e1-8a358b3760b3@suse.com>
Date: Tue, 10 Jun 2025 09:52:02 +0300
From: Nikolay Borisov <nik.borisov@...e.com>
To: Chao Gao <chao.gao@...el.com>
Cc: linux-coco@...ts.linux.dev, x86@...nel.org, kvm@...r.kernel.org,
 seanjc@...gle.com, pbonzini@...hat.com, eddie.dong@...el.com,
 kirill.shutemov@...el.com, dave.hansen@...el.com, dan.j.williams@...el.com,
 kai.huang@...el.com, isaku.yamahata@...el.com, elena.reshetova@...el.com,
 rick.p.edgecombe@...el.com, Farrah Chen <farrah.chen@...el.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 03/20] x86/virt/seamldr: Introduce a wrapper for
 P-SEAMLDR SEAMCALLs

On 6/10/25 04:03, Chao Gao wrote:
> On Mon, Jun 09, 2025 at 11:02:49AM +0300, Nikolay Borisov wrote:
>>
>>
>> On 6/9/25 10:53, Chao Gao wrote:
>>>>> +config INTEL_TDX_MODULE_UPDATE
>>>>> +	bool "Intel TDX module runtime update"
>>>>> +	depends on INTEL_TDX_HOST
>>>>> +	help
>>>>> +	  This enables the kernel to support TDX module runtime update. This allows
>>>>> +	  the admin to upgrade the TDX module to a newer one without the need to
>>>>> +	  terminate running TDX guests.
>>>>> +
>>>>> +	  If unsure, say N.
>>>>> +
>>>>
>>>> WHy should this be conditional?
>>>>
>>>
>>> Good question. I don't have a strong reason, but here are my considerations:
>>>
>>> 1. Runtime updates aren't strictly necessary for TDX functionalities. Users can
>>>      update the TDX module via BIOS updates and reboot if service downtime isn't
>>>      a concern.
>>>
>>> 2. Selecting TDX module updates requires selecting FW_UPLOAD and FW_LOADER,
>>>      which I think will significantly increase the kernel size if FW_UPLOAD/LOADER
>>>      won't otherwise be selected.
>>
>> If size is a consideration (but given the size of machines that are likely to
>> run CoCo guests I'd say it's not) then don't make this a user-configurable
>> option but rather make it depend on TDX being selected and
>> FW_UPLOAD/FW_LOADER being selected.
> 
> But in almost all existing cases, 'select FW_UPLOAD/LOADER' is used rather than
> 'depends on FW_UPLOAD/LOADER'. You can verify this by running
> 
> 	find . -name 'Kconfig' -exec grep -E 'FW_UPLOAD|FW_LOADER$' {} +

Then just have TDX select FW_UPLOAD/FW_LOADER and be done with it. 
Still, let's hear other opinions but in this case I'd say size 
considerations aren't major so let's make it simpler for the user.

> 
>>
>> I'd rather keep the user visible options to a minimum, especially something
>> such as this update functionality.
>>
>> But in any case I'd like to hear other opinions as well.
> 
> Yeah, let's see what others think.
> 
> <snip>