linux-kernel - Re: [PATCH] tpm_tis: Add missing start/stop_tpm

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Date:   Tue, 2 Feb 2021 18:17:34 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     James Bottomley <James.Bottomley@...senpartnership.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Łukasz Majczak <lma@...ihalf.com>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        Radoslaw Biernacki <rad@...ihalf.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Alex Levin <levinale@...gle.com>
Subject: Re: [PATCH] tpm_tis: Add missing start/stop_tpm_chip calls

On Sat, Jan 30, 2021 at 04:41:13PM -0800, James Bottomley wrote:
> On Sat, 2021-01-30 at 15:49 -0800, Guenter Roeck wrote:
> > On 1/29/21 2:59 PM, Jarkko Sakkinen wrote:
> > > On Tue, Jan 26, 2021 at 04:46:07PM +0100, Łukasz Majczak wrote:
> > > > Hi Jarkko, Guenter
> > > > 
> > > > Yes, here are the logs when failure occurs -
> > > > https://gist.github.com/semihalf-majczak-lukasz/1575461f585f1e7fb1e9366b8eceaab9
> > > > Look for a phrase "TPM returned invalid status"
> > > > 
> > > > Guenter - good suggestion - I will try to keep it as tight as
> > > > possible.
> > > > 
> > > > Best regards,
> > > > Lukasz
> > > 
> > > Is it possible for you try out with linux-next? Thanks. It's a
> > > known issue, which ought to be fixed by now.
> > > 
> > > The log message is harmless, it'a warning not panic, and does not
> > > endanger system stability. WARN()'s always dump stack trace. No
> > > oops is happening.
> > > 
> > 
> > There is a note in the kernel documentation which states:
> > 
> > Note that the WARN()-family should only be used for "expected to
> > be unreachable" situations. If you want to warn about "reachable
> > but undesirable" situations, please use the pr_warn()-family of
> > functions.
> 
> It fits the definition.  The warning only triggers if the access is in
> the wrong locality, which should be impossible, so the warning should
> be unreachable.

It's an overkill. Even in perfectly working kernel it's not impossible, as
sometimes hardware gives faulty data. I think that it also lacks the useful
information i.e. the status code.

I would useful WARN() only if the driver state could suffer. In this case
it doesn't. It only results failing transfer but kernel state is still
legit.

/Jarkko
>