linux-kernel - Re: [v4.0][v4.1][v4.2][Regression] tpm: fix raciness of PPI interface lookup

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Date:	Mon, 14 Sep 2015 16:26:49 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Joseph Salisbury <joseph.salisbury@...onical.com>
Cc:	jarkko.sakkinen@...ux.intel.com,
	jason.gunthorpe@...idianresearch.com, stefanb@...ux.vnet.ibm.com,
	Scot Doyle <lkml14@...tdoyle.com>, peterhuewe@....de,
	tpmdd@...horst.net, tpmdd-devel@...ts.sourceforge.net,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [v4.0][v4.1][v4.2][Regression] tpm: fix raciness of PPI
 interface lookup

On Mon, Sep 14, 2015 at 05:36:07PM -0400, Joseph Salisbury wrote:
> I was hoping to get your feedback, since you are the patch author.  Do
> you think gathering any additional data will help diagnose this
> issue,

Jarkko may have more to add, but from my perspective, this should have
been a no-functional change re-work patch. I'm surprised this has been
tagged, since it doesn't seem to really change much at all. I looked
again and all the code motion looks right to me.

The biggest change is that we don't call acpi_walk_namespace to get
the acpi_dev_handle, instead this now comes from pnp_acpi_device. It
would be useful to know if that is the source of the difference. ie
are the two methods are giving different answers on this hardware?

I'd also test with this line:

+       if (pnp_acpi_device(pnp_dev))
+               acpi_dev_handle = pnp_acpi_device(pnp_dev)->handle;

Changed to 'acpi_dev_handle = NULL;' - that should totally disable TPM
access to ACPI.

The ACPI code doesn't actually do anything if sysfs files are not
touched, I'm really not sure how it could be at fault.. Maybe also
comment out the sysfs_create_group, could something be touching the
files in userspace?

Honestly, I don't know enough about ACPI to guess what is going
on. Hopefully Jarkko does..

Jason
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