linux-kernel - Re: [PATCH] x86: tpm: Remove a busy bit of the NVS area for supporting AMD's fTPM

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Date:   Thu, 29 Aug 2019 18:39:17 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Seunghun Han <kkamagui@...il.com>
Cc:     Matthew Garrett <mjg59@...f.ucam.org>,
        Matthew Garrett <mjg59@...gle.com>,
        Peter Huewe <peterhuewe@....de>,
        "open list:TPM DEVICE DRIVER" <linux-integrity@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: tpm: Remove a busy bit of the NVS area for
 supporting AMD's fTPM

On Thu, Aug 29, 2019 at 06:34:37PM +0300, Jarkko Sakkinen wrote:
> On Wed, Aug 28, 2019 at 06:36:04PM +0900, Seunghun Han wrote:
> > >
> > > On Wed, Aug 28, 2019 at 01:36:30AM +0900, Seunghun Han wrote:
> > >
> > > > I got your point. Is there any problem if some regions which don't
> > > > need to be handled in NVS area are saved and restored? If there is a
> > > > problem, how about adding code for ignoring the regions in NVS area to
> > > > the nvs.c file like Jarkko said? If we add the code, we can save and
> > > > restore NVS area without driver's interaction.
> > >
> > > The only thing that knows which regions should be skipped by the NVS
> > > driver is the hardware specific driver, so the TPM driver needs to ask
> > > the NVS driver to ignore that region and grant control to the TPM
> > > driver.
> > >
> > > --
> > > Matthew Garrett | mjg59@...f.ucam.org
> > 
> > Thank you, Matthew and Jarkko.
> > It seems that the TPM driver needs to handle the specific case that
> > TPM regions are in the NVS. I would make a patch that removes TPM
> > regions from the ACPI NVS by requesting to the NVS driver soon.
> > 
> > Jarkko,
> > I would like to get some advice on it. What do you think about
> > removing TPM regions from the ACPI NVS in TPM CRB driver? If you don't
> > mind, I would make the patch about it.
> 
> I'm not sure if ignoring is right call. Then the hibernation behaviour
> for TPM regions would break.
> 
> Thus, should be "ask access" rather than "grant control".

Or "reserve access" as NVS driver does not have intelligence to do any
policy based decision here.

A function that gets region and then checks if NVS driver has matching
one and returns true/false based on that should be good enough. Then
you raw ioremap() in the TPM driver.

/Jarkko