linux-kernel - Re: [PATCH v2] tpm, tpm_tis: Fix timeout handling when waiting for TPM status

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Message-ID: <Z9AHA0rhq3A1bhGt@kernel.org>
Date: Tue, 11 Mar 2025 11:48:51 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Jonathan McDowell <noodles@...th.li>
Cc: Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
	Lino Sanfilippo <l.sanfilippo@...bus.com>,
	Michal Suchánek <msuchanek@...e.de>,
	linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tpm, tpm_tis: Fix timeout handling when waiting for
 TPM status

On Mon, Mar 10, 2025 at 12:22:08PM +0000, Jonathan McDowell wrote:
> The change to only use interrupts to handle supported status changes
> introduced an issue when it is necessary to poll for the status. Rather
> than checking for the status after sleeping the code now sleeps after
> the check. This means a correct, but slower, status change on the part
> of the TPM can be missed, resulting in a spurious timeout error,
> especially on a more loaded system. Switch back to sleeping *then*
> checking. An up front check of the status has been done at the start of
> the function, so this does not 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>
> Reviewed-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
> ---
> v2: Reword commit message
>     Don't needlessly wrap line
> 
>  drivers/char/tpm/tpm_tis_core.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index fdef214b9f6b..c969a1793184 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -114,11 +114,10 @@ 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
> 

Probably apply late this and timeout fix late this week.

Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

BR, Jarkko