linux-kernel - Re: [PATCH 0/4] tsm: Unified Measurement Register ABI for TVMs

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Message-ID: <d8f3eb33-d902-4391-adc7-005e4895b471@intel.com>
Date: Thu, 13 Feb 2025 15:50:19 -0600
From: "Xing, Cedric" <cedric.xing@...el.com>
To: Dave Hansen <dave.hansen@...el.com>, Dan Williams
	<dan.j.williams@...el.com>, "Kirill A. Shutemov"
	<kirill.shutemov@...ux.intel.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, <x86@...nel.org>, "H. Peter Anvin"
	<hpa@...or.com>
CC: <linux-kernel@...r.kernel.org>, <linux-coco@...ts.linux.dev>, "Kuppuswamy
 Sathyanarayanan" <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH 0/4] tsm: Unified Measurement Register ABI for TVMs

On 2/13/2025 10:58 AM, Dave Hansen wrote:
> On 2/13/25 08:21, Xing, Cedric wrote:
>> On 2/12/2025 10:50 PM, Dave Hansen wrote:
>>> On 2/12/25 18:23, Cedric Xing wrote:
>>>> NOTE: This patch series introduces the Measurement Register (MR) ABI,
>>>> and
>>>> is a continuation of the RFC series on the same topic [1].
>>>
>>> Could you please explain how the benefits of this series are helpful to
>>> end users?
>>
>> This series exposes MRs as sysfs attributes, allowing end users to
>> access them effortlessly without needing to write any code. This
>> simplifies the process of debugging and diagnosing measurement-related
>> issues. Additionally, it makes the CC architecture more intuitive for
>> newcomers.
> 
> Wait a sec, so there's already ABI for manipulating these? This just
> adds a parallel sysfs interface to the existing ABI?
> 
No, this is new. There's no existing ABI for accessing measurement 
registers from within a TVM (TEE VM). Currently, on TDX for example, 
reading TDX measurement registers (MRs) must be done by getting a TD 
quote. And there's no way to extend any RTMRs. Therefore, it would be 
much easier end users to debug/diagnose measurement related issues 
(which would almost always require reading MRs) with this patch.

> Also, you're saying that users don't need to write any code, but then
> provide... sample code. That's unexpected.
> 
The sample code is to demo how to expose MRs from a CC guest driver, but 
not for end users to access those MRs.

> Oh, and you seem to have forgotten to attach the sysfs ABI documentation
> patch to the series. You did write the required documentation, right? ;)
Documentation/ABI/testing/sysfs-kernel-tsm (new file added by patch 1) 
contains a description on the attributes added by the patch.