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

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Date:   Tue, 7 Nov 2017 23:59:10 +0530
From:   Nayna Jain <nayna@...ux.vnet.ibm.com>
To:     Alexander.Steffen@...ineon.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



On 10/20/2017 08:12 PM, Alexander.Steffen@...ineon.com wrote:
>> 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.

Thanks Alex for testing these.. Did you get the chance to do any further 
analysis ?

Thanks & Regards,
        - Nayna

> Alexander
>