linux-kernel - Re: [PATCH] tpm, tpm_tis: Fix timeout handling when waiting for TPM status

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Message-ID: <8117d025-3ea9-4b1e-bd34-493886c92c30@kunbus.com>
Date: Fri, 7 Mar 2025 09:38:49 +0100
From: Lino Sanfilippo <l.sanfilippo@...bus.com>
To: Jonathan McDowell <noodles@...th.li>, Jarkko Sakkinen
 <jarkko@...nel.org>, Peter Huewe <peterhuewe@....de>,
 Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm, tpm_tis: Fix timeout handling when waiting for TPM
 status


Hi Jonathan,

On 05.03.25 10:45, Jonathan McDowell wrote:

> From: Jonathan McDowell <noodles@...a.com>
> 
> The change to only use interrupts to handle supported status changes,
> then switch to polling for the rest, inverted the status test and sleep
> such that we can end up sleeping beyond our timeout and not actually
> checking the status. This can result in spurious TPM timeouts,
> especially on a more loaded system. Fix by switching the order back so
> we sleep *then* check. We've done a up front check when we enter the
> function so this won't cause an additional delay when the status is
> already what we're looking for.
> 
> Cc: stable@...r.kernel.org # v6.4+
> Fixes: e87fcf0dc2b4 ("tpm, tpm_tis: Only handle supported interrupts")
> Signed-off-by: Jonathan McDowell <noodles@...a.com>
> Reviewed-by: Michal Suchánek <msuchanek@...e.de>
> ---
>  drivers/char/tpm/tpm_tis_core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index fdef214b9f6b..167d71747666 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -114,11 +114,11 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
>                 return 0;
>         /* process status changes without irq support */
>         do {
> +               usleep_range(priv->timeout_min,
> +                            priv->timeout_max);
>                 status = chip->ops->status(chip);
>                 if ((status & mask) == mask)
>                         return 0;
> -               usleep_range(priv->timeout_min,
> -                            priv->timeout_max);
>         } while (time_before(jiffies, stop));
>         return -ETIME;
>  }
> --
> 2.48.1
> 

FWIW:
Reviewed-by: Lino Sanfilippo <l.sanfilippo@...bus.com>

I cannot remember any more but I think the change of the logic in 
the while loop must have been a leftover from some tests I did
at this time. However it should not have been part of the patch, so
good that you found it and thanks for the fix!

BR,
Lino