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

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Message-ID: <CAHjaAcQyCgfc+JbVNa_ix1HY64K3NCY5octj26j=o64EDtPkGw@mail.gmail.com>
Date:   Sat, 31 Aug 2019 01:13:11 +0900
From:   Seunghun Han <kkamagui@...il.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.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 2/2] tpm: tpm_crb: enhance resource mapping mechanism for
 supporting AMD's fTPM

>
> On Fri, Aug 30, 2019 at 10:54:59PM +0900, Seunghun Han wrote:
>
> > When I tested this patch in my machine, it seemed that ACPI NVS was
> > saved after TPM CRB driver sent "TPM2_Shutdown(STATE)" to the fTPM
> > while suspending. Then, ACPI NVS was restored while resuming.
> > After resuming, PCRs didn't change and TPM2 tools such as
> > tpm2_pcrlist, tpm2_extend, tpm2_getrandoms worked well.
> > So, according to my test result, it seems that the patch doesn't
> > create bugs and race during resume.
>
> I have a feeling that is shear luck of link time ordering and not guarenteed??
>
> Jason

No, it is guaranteed. As you know, suspend_nvs_save() is called by
acpi_pm_pre_suspend(), and it is called by
platform_suspend_prepare_noirq(). platform_suspend_prepare_noirq() is
also called by suspend_enter(), and it already suspends all devices
like TPM CRB driver before calling platform_suspend_prepare_noirq().
This means that the order is guaranteed and we don't need to worry about it.

Seunghun