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

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Message-ID: <aEeEbXZglywwo1Rm@intel.com>
Date: Tue, 10 Jun 2025 09:03:41 +0800
From: Chao Gao <chao.gao@...el.com>
To: Nikolay Borisov <nik.borisov@...e.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 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$' {} +

>
>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>