linux-kernel - Re: [PATCH v2] tpm: Allow system suspend to continue when TPM suspend fails

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Date:   Fri, 6 Jan 2023 10:59:50 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Thorsten Leemhuis <regressions@...mhuis.info>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>, Jan Dabros <jsd@...ihalf.com>,
        regressions@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>,
        linux-integrity@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Johannes Altmanninger <aclopte@...il.com>,
        stable@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        tbroch@...omium.org, semenzato@...omium.org,
        dbasehore@...omium.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2] tpm: Allow system suspend to continue when TPM suspend fails

On Thu, Jan 5, 2023 at 7:02 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> In lieu of actually fixing the underlying bug, just allow system suspend
> to continue, so that laptops still go to sleep fine. Later, this can be
> reverted when the real bug is fixed.

So the patch looks fine to me, but since there's still the ChromeOS
discussion pending I'll wait for that to finish.

Perhaps re-send or at least remind me if/when it does?

Also, a query about the printout:

> +       if (rc)
> +               pr_err("Unable to suspend tpm-%d (error %d), but continuing system suspend\n",
> +                      chip->dev_num, rc);

so I suspect that 99% of the time the dev_num isn't actually all that
useful, but what *might* be useful is which tpm driver it is.

Just comparing the error dmesg output you had:

  ..
  tpm tpm0: Error (28) sending savestate before suspend
  tpm_tis 00:08: PM: __pnp_bus_suspend(): tpm_pm_suspend+0x0/0x80 returns 28
  ..

that "tpm tpm0" output is kind of useless compared to the "tpm_tis 00:08" one.

So I think "dev_err(dev, ...)" would be more useful here.

Finally - and maybe I'm just being difficult here, I will note here
again that TPM2 devices don't have this issue, because the TPM2 path
for suspend doesn't do any of this at all.

It just does

        tpm_transmit_cmd(..);

with a TPM2_CC_SHUTDOWN TPM_SU_STATE command, and doesn't even check
the return value. In fact, the tpm2 code *used* to have this comment:

        /* In places where shutdown command is sent there's no much we can do
         * except print the error code on a system failure.
         */
        if (rc < 0 && rc != -EPIPE)
                dev_warn(&chip->dev, "transmit returned %d while
stopping the TPM",
                         rc);

but it was summarily removed when doing some re-organization around
buffer handling.

So just by looking at what tpm2 does, I'm not 100% convinced that tpm1
should do this dance at all.

But having a dev_err() is probably a good idea at least as a transitional thing.

                  Linus