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Date:   Tue, 27 Aug 2019 15:47:07 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Matthew Garrett <mjg59@google.com>
Cc:     Seunghun Han <kkamagui@gmail.com>,
        Matthew Garrett <mjg59@srcf.ucam.org>,
        Peter Huewe <peterhuewe@gmx.de>,
        "open list:TPM DEVICE DRIVER" <linux-integrity@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: tpm: Remove a busy bit of the NVS area for
 supporting AMD's fTPM
Message-ID: <20190827124707.yhqtaqa4ur6i45h7@linux.intel.com>
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On Mon, Aug 26, 2019 at 10:40:25AM -0700, Matthew Garrett wrote:
> On Mon, Aug 26, 2019 at 1:18 AM Seunghun Han <kkamagui@gmail.com> wrote:
> > To support AMD's fTPM, I removed the busy bit from the ACPI NVS area like
> > the reserved area so that AMD's fTPM regions could be assigned in it.
> 
> drivers/acpi/nvs.c saves and restores the contents of NVS regions, and
> if other drivers use these regions without any awareness of this then
> things may break. I'm reluctant to say that just unilaterally marking
> these regions as available is a good thing, but it's clearly what's
> expected by AMD's implementation. One approach would be to have a
> callback into the nvs code to indicate that a certain region should be
> handed off to a driver, which would ensure that we can handle this on
> a case by case basis?

What if E820 would just have a small piece of code just for fTPM's e.g.
it would check the ACPI tree for fTPM's and ignore TPM regions.

/Jarkko