linux-kernel - Re: [REGRESSION][BISECTED] tpm: Popping noise in USB headphones since 1b6d7f9eb150

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Message-ID: <ce7fa562-7cb7-4adc-934a-560b94ce44f0@linux.ibm.com>
Date: Mon, 2 Dec 2024 17:15:16 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: Jarkko Sakkinen <jarkko@...nel.org>,
        Christian Heusel <christian@...sel.eu>
Cc: Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        regressions@...ts.linux.dev
Subject: Re: [REGRESSION][BISECTED] tpm: Popping noise in USB headphones since
 1b6d7f9eb150



On 11/29/24 9:44 PM, Jarkko Sakkinen wrote:
> On Tue Nov 26, 2024 at 1:42 PM EET, Christian Heusel wrote:
>> On 24/10/25 05:47PM, Jarkko Sakkinen wrote:
>>> Yeah, this is on the list.
>>>
>>> See: https://bugzilla.kernel.org/show_bug.cgi?id=219383#c5
>>>
>>> I had a fix for the AMD boot-time issue already over a month ago
>>> but unfortunately took time to get enough feedback.
>>>
>>> BR, Jarkko
>>
>> I'm not sure if this is supposed to be fixed, but AFAIK we hoped that
>> the patchset that was mentioned in bugzilla also helped this issue.
>>
>> The reporter said that the bug is still present in 6.12.1, so this might
>> need further poking 🤔
> 
> I'd suggest a workaround for the time being.
> 
> In 6.12 we added this for (heavy) IMA use:
> 
> tpm.disable_pcr_integrity= [HW,TPM]
>                          Do not protect PCR registers from unintended physical
>                          access, or interposers in the bus by the means of
>                          having an integrity protected session wrapped around
>                          TPM2_PCR_Extend command. Consider this in a situation
>                          where TPM is heavily utilized by IMA, thus protection
>                          causing a major performance hit, and the space where
>                          machines are deployed is by other means guarded.
> 
> Similarly it might make sense to have "tpm.disable_random_integrity"
> that disables the feature introduced by the failing commit.
> 

I am wondering what could be the not-so-obvious root cause for this? 
Could it be due to a (TPM or RNG-related) lock? I guess the audio 
popping could occur if an application cannot meet timing requirements 
when it runs into some sort of blocking lock...

> What do you think?
 > >>
>> Cheers,
>> Chris
> 
> BR, Jarkko
>