linux-kernel - RE: [PATCH v4 2/4] tpm: ignore burstcount to improve tpm

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Date:   Fri, 20 Oct 2017 14:42:54 +0000
From:   <Alexander.Steffen@...ineon.com>
To:     <nayna@...ux.vnet.ibm.com>, <linux-integrity@...r.kernel.org>
CC:     <zohar@...ux.vnet.ibm.com>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <peterhuewe@....de>,
        <jarkko.sakkinen@...ux.intel.com>, <tpmdd@...horst.net>,
        <jgunthorpe@...idianresearch.com>, <patrickc@...ibm.com>
Subject: RE: [PATCH v4 2/4] tpm: ignore burstcount to improve tpm_tis send()
 performance

> The TPM burstcount status indicates the number of bytes that can
> be sent to the TPM without causing bus wait states.  Effectively,
> it is the number of empty bytes in the command FIFO.
> 
> This patch optimizes the tpm_tis_send_data() function by checking
> the burstcount only once. And if the burstcount is valid, it writes
> all the bytes at once, permitting wait state.
> 
> After this change, performance on a TPM 1.2 with an 8 byte
> burstcount for 1000 extends improved from ~41sec to ~14sec.
> 
> Suggested-by: Ken Goldman <kgold@...ux.vnet.ibm.com> in
> conjunction with the TPM Device Driver work group.
> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>
> Acked-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> ---
>  drivers/char/tpm/tpm_tis_core.c | 42 +++++++++++++++----------------------
> ----
>  1 file changed, 15 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c
> b/drivers/char/tpm/tpm_tis_core.c
> index b33126a35694..993328ae988c 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -316,7 +316,6 @@ static int tpm_tis_send_data(struct tpm_chip *chip,
> u8 *buf, size_t len)
>  {
>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>  	int rc, status, burstcnt;
> -	size_t count = 0;
>  	bool itpm = priv->flags & TPM_TIS_ITPM_WORKAROUND;
> 
>  	status = tpm_tis_status(chip);
> @@ -330,35 +329,24 @@ static int tpm_tis_send_data(struct tpm_chip *chip,
> u8 *buf, size_t len)
>  		}
>  	}
> 
> -	while (count < len - 1) {
> -		burstcnt = get_burstcount(chip);
> -		if (burstcnt < 0) {
> -			dev_err(&chip->dev, "Unable to read burstcount\n");
> -			rc = burstcnt;
> -			goto out_err;
> -		}
> -		burstcnt = min_t(int, burstcnt, len - count - 1);
> -		rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv-
> >locality),
> -					 burstcnt, buf + count);
> -		if (rc < 0)
> -			goto out_err;
> -
> -		count += burstcnt;
> -
> -		if (wait_for_tpm_stat(chip, TPM_STS_VALID, chip-
> >timeout_c,
> -					&priv->int_queue, false) < 0) {
> -			rc = -ETIME;
> -			goto out_err;
> -		}
> -		status = tpm_tis_status(chip);
> -		if (!itpm && (status & TPM_STS_DATA_EXPECT) == 0) {
> -			rc = -EIO;
> -			goto out_err;
> -		}
> +	/*
> +	 * Get the initial burstcount to ensure TPM is ready to
> +	 * accept data.
> +	 */
> +	burstcnt = get_burstcount(chip);
> +	if (burstcnt < 0) {
> +		dev_err(&chip->dev, "Unable to read burstcount\n");
> +		rc = burstcnt;
> +		goto out_err;
>  	}
> 
> +	rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv->locality),
> +			len - 1, buf);
> +	if (rc < 0)
> +		goto out_err;
> +
>  	/* write last byte */
> -	rc = tpm_tis_write8(priv, TPM_DATA_FIFO(priv->locality),
> buf[count]);
> +	rc = tpm_tis_write8(priv, TPM_DATA_FIFO(priv->locality), buf[len-
> 1]);
>  	if (rc < 0)
>  		goto out_err;
> 
> --
> 2.13.3

This seems to fail reliably with my SPI TPM 2.0. I get EIO when trying to send large amounts of data, e.g. with TPM2_Hash, and subsequent tests seem to take an unusual amount of time. More analysis probably has to wait until November, since I am going to be in Prague next week.

Alexander