linux-kernel - Re: [PATCH] tpm: Add explicit chip->ops locking for sysfs attributes.

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Date:   Tue, 21 Nov 2017 01:49:47 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Peter Huewe <peterhuewe@....de>,
        Andrey Pronin <apronin@...omium.org>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: Add explicit chip->ops locking for sysfs attributes.

On Mon, Nov 20, 2017 at 04:17:28PM -0700, Jason Gunthorpe wrote:
> On Mon, Nov 20, 2017 at 02:45:23PM -0800, Guenter Roeck wrote:
> 
> > "tpm: Enable sysfs support for TPM2 devices
> > 
> > Access to chip->ops on TPM2 devices requires an explicit lock,
> > since the pointer is set to NULL in tpm_class_shutdown().
> > Implement that lock for sysfs access functions and enable sysfs
> > support for TPM2 devices."
> 
> Wait.. one of the reasons we let it go with no sysfs for so long was
> because there was not many sysfs files that were compatible with tpm2?
> 
> For TPM2 we have sort of had an API break of sorts from TPM1 in a
> couple places around sysfs, and I would like to not re-introduce any
> badly designed sysfs files for TPM2..
> 
> So.. When you apply this patch, what changes actually happen in the
> sysfs directory?
> 
> Jason

Oops. I was too quick. This will cause all the TPM 1.x attributes
added also for TPM 2.0. That's not a great idea. The tpm_dev_group
should be only assigned for TPM 1.x devices. This commit should only
enable addition of sysfs attributes for TPM 2.0 devices.

/Jarkko