linux-kernel - Re: [PATCH v2 2/2] tpm: tpm_crb: enhance resource mapping mechanism for supporting AMD's fTPM

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Date:   Tue, 10 Sep 2019 16:06:29 +0100
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Seunghun Han <kkamagui@...il.com>
Cc:     Peter Huewe <peterhuewe@....de>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        "open list:TPM DEVICE DRIVER" <linux-integrity@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Vanya Lazeev <ivan.lazeev@...il.com>
Subject: Re: [PATCH v2 2/2] tpm: tpm_crb: enhance resource mapping mechanism
 for supporting AMD's fTPM

On Tue, Sep 10, 2019 at 03:42:15PM +0100, Jarkko Sakkinen wrote:
> On Mon, Sep 09, 2019 at 06:09:06PM +0900, Seunghun Han wrote:
> > I got an AMD system which had a Ryzen Threadripper 1950X and MSI
> > mainboard, and I had a problem with AMD's fTPM. My machine showed an error
> > message below, and the fTPM didn't work because of it.
> > 
> > [  5.732084] tpm_crb MSFT0101:00: can't request region for resource
> >              [mem 0x79b4f000-0x79b4ffff]
> > [  5.732089] tpm_crb: probe of MSFT0101:00 failed with error -16
> > 
> > When I saw the iomem, I found two fTPM regions were in the ACPI NVS area. 
> > The regions are below.
> > 
> > 79a39000-79b6afff : ACPI Non-volatile Storage
> >   79b4b000-79b4bfff : MSFT0101:00
> >   79b4f000-79b4ffff : MSFT0101:00
> > 
> > After analyzing this issue, I found that crb_map_io() function called
> > devm_ioremap_resource() and it failed. The ACPI NVS didn't allow the TPM
> > CRB driver to assign a resource in it because a busy bit was set to
> > the ACPI NVS area.
> > 
> > To support AMD's fTPM, I added a function to check intersects between
> > the TPM region and ACPI NVS before it mapped the region. If some
> > intersects are detected, the function just calls devm_ioremap() for
> > a workaround. If there is no intersect, it calls devm_ioremap_resource().
> > 
> > Signed-off-by: Seunghun Han <kkamagui@...il.com>
> 
> This problem is still valid and not addressed by Vanya's patch (and
> should not be as it is a disjoint issue).  However, calling
> devm_ioremap() is somewhat racy as the NVS driver is not aware of that.
> 
> My take is that this should be fixed in the code that assigns regions to
> the NVS driver e.g. it could look up the regions assigned to the
> MSFT0101 and ignore those regions. In the end linux-acpi maintainers
> have the say on this but this would be the angle that I'd take to
> implement such patch probably.

Matthew pointed out that having a hook in NVS driver is better solution
because it is nil functionality if the TPM driver is loaded. We need
functions to:

1. Request a region from the NVS driver (when tpm_crb loads)
2. Release a region back to the NVS Driver (when tpm_crb unloads).

My proposal would unnecessarily duplicate code and also leave a
side-effect when TPM is not used in the first place.

I see this as the overally best solution. If you can come up with a
patch for the NVS side and changes to CRB drivers to utilize the new
hooks, then combined with Vanya's changes we have a sustainable solution
for AMD fTPM.

/Jarkko