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

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Message-ID: <CACdnJutfR2X-5ksXw4PNUdyH2MJs_mExNCcYPp8NLcPW2EDrYQ@mail.gmail.com>
Date:   Tue, 27 Aug 2019 09:10:45 -0700
From:   Matthew Garrett <mjg59@...gle.com>
To:     Seunghun Han <kkamagui@...il.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        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 Tue, Aug 27, 2019 at 1:23 AM Seunghun Han <kkamagui@...il.com> wrote:
> If the regions allocated in the NVS region need to be handled by a
> driver, the callback mechanism is good for it. However, this case
> doesn't need it because the regions allocated in NVS are just I/O
> regions.
>
> In my opinion, if the driver wants to handle the region in the NVS
> while suspending or hibernating, it has to use register_pm_notifier()
> function and handle the event. We already had the mechanism that could
> ensure that the cases you worried about would be handled, so it seems
> to me that removing the busy bit from the NVS region is fine.

No. The NVS regions are regions that need to be saved and restored
over hibernation, but which aren't otherwise handled by a driver -
that's why the NVS code exists. If drivers are allowed to bind to NVS
regions without explicit handling, they risk conflicting with that.