Re: [PATCH v8 08/11] tpm, tpm: Implement usage counter for locality

[Lino Sanfilippo]

On 23.10.22 06:40, Jarkko Sakkinen wrote:
> On Tue, Oct 18, 2022 at 01:57:29AM +0200, Lino Sanfilippo wrote:
>> From: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
>>
>> Implement a usage counter for the (default) locality used by the TPM TIS
>> driver:
>> Request the locality from the TPM if it has not been claimed yet, otherwise
>> only increment the counter. Also release the locality if the counter is 0
>> otherwise only decrement the counter. Ensure thread-safety by protecting
>> the counter with a mutex.
>>
>> This allows to request and release the locality from a thread and the
>> interrupt handler at the same time without the danger to interfere with
>> each other.
>>
>> By doing this refactor the names of the amended functions to use the proper
>> prefix.
>>
>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
>> Tested-by: Michael Niewöhner <linux@xxxxxxxxxxxxxx>
>> ---
>>  drivers/char/tpm/tpm_tis_core.c | 75 ++++++++++++++++++++++-----------
>>  drivers/char/tpm/tpm_tis_core.h |  2 +
>>  2 files changed, 53 insertions(+), 24 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
>> index 4336f7ea8c2b..79dfab65976f 100644
>> --- a/drivers/char/tpm/tpm_tis_core.c
>> +++ b/drivers/char/tpm/tpm_tis_core.c
>> @@ -165,16 +165,27 @@ static bool check_locality(struct tpm_chip *chip, int l)
>>  	return false;
>>  }
>>
>> -static int release_locality(struct tpm_chip *chip, int l)
>> +static int tpm_tis_release_locality_locked(struct tpm_tis_data *priv, int l)
>
> Nit: usually you would actually use "unlocked" here, not locked.
>
> Probably best name would be __tpm_tis_release_locality().


Agreed. This is also consistent with the naming scheme used for many other
kernel functions.

>
>> +{
>> +	tpm_tis_write8(priv, TPM_ACCESS(l), TPM_ACCESS_ACTIVE_LOCALITY);
>> +
>> +	return 0;
>> +}
>> +
>> +static int tpm_tis_release_locality(struct tpm_chip *chip, int l)
>>  {
>>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>>
>> -	tpm_tis_write8(priv, TPM_ACCESS(l), TPM_ACCESS_ACTIVE_LOCALITY);
>> +	mutex_lock(&priv->locality_count_mutex);
>> +	priv->locality_count--;
>> +	if (priv->locality_count == 0)
>> +		tpm_tis_release_locality_locked(priv, l);
>> +	mutex_unlock(&priv->locality_count_mutex);
>>
>>  	return 0;
>>  }
>
> Since the function pointer has the word "relinquish" and not "release",
> perhaps these should also use that word for consistency.
>
>>
>> -static int request_locality(struct tpm_chip *chip, int l)
>> +static int tpm_tis_request_locality_locked(struct tpm_chip *chip, int l)
>>  {
>>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>>  	unsigned long stop, timeout;
>> @@ -215,6 +226,20 @@ static int request_locality(struct tpm_chip *chip, int l)
>>  	return -1;
>>  }
>>
>> +static int tpm_tis_request_locality(struct tpm_chip *chip, int l)
>> +{
>> +	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>> +	int ret = 0;
>> +
>> +	mutex_lock(&priv->locality_count_mutex);
>> +	if (priv->locality_count == 0)
>> +		ret = tpm_tis_request_locality_locked(chip, l);
>> +	if (!ret)
>> +		priv->locality_count++;
>> +	mutex_unlock(&priv->locality_count_mutex);
>> +	return ret;
>> +}
>> +
>>  static u8 tpm_tis_status(struct tpm_chip *chip)
>>  {
>>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>> @@ -682,7 +707,7 @@ static int probe_itpm(struct tpm_chip *chip)
>>  	if (vendor != TPM_VID_INTEL)
>>  		return 0;
>>
>> -	if (request_locality(chip, 0) != 0)
>> +	if (tpm_tis_request_locality(chip, 0) != 0)
>>  		return -EBUSY;
>>
>>  	rc = tpm_tis_send_data(chip, cmd_getticks, len);
>> @@ -703,7 +728,7 @@ static int probe_itpm(struct tpm_chip *chip)
>>
>>  out:
>>  	tpm_tis_ready(chip);
>> -	release_locality(chip, priv->locality);
>> +	tpm_tis_release_locality(chip, priv->locality);
>>
>>  	return rc;
>>  }
>> @@ -762,7 +787,7 @@ static int tpm_tis_gen_interrupt(struct tpm_chip *chip)
>>  	cap_t cap;
>>  	int ret;
>>
>> -	ret = request_locality(chip, 0);
>> +	ret = tpm_tis_request_locality(chip, 0);
>>  	if (ret < 0)
>>  		return ret;
>>
>> @@ -771,7 +796,7 @@ static int tpm_tis_gen_interrupt(struct tpm_chip *chip)
>>  	else
>>  		ret = tpm1_getcap(chip, TPM_CAP_PROP_TIS_TIMEOUT, &cap, desc, 0);
>>
>> -	release_locality(chip, 0);
>> +	tpm_tis_release_locality(chip, 0);
>>
>>  	return ret;
>>  }
>> @@ -796,33 +821,33 @@ static int tpm_tis_probe_irq_single(struct tpm_chip *chip, u32 intmask,
>>  	}
>>  	priv->irq = irq;
>>
>> -	rc = request_locality(chip, 0);
>> +	rc = tpm_tis_request_locality(chip, 0);
>>  	if (rc < 0)
>>  		return rc;
>>
>>  	rc = tpm_tis_read8(priv, TPM_INT_VECTOR(priv->locality),
>>  			   &original_int_vec);
>>  	if (rc < 0) {
>> -		release_locality(chip, priv->locality);
>> +		tpm_tis_release_locality(chip, priv->locality);
>>  		return rc;
>>  	}
>>
>>  	rc = tpm_tis_write8(priv, TPM_INT_VECTOR(priv->locality), irq);
>>  	if (rc < 0) {
>> -		release_locality(chip, priv->locality);
>> +		tpm_tis_release_locality(chip, priv->locality);
>>  		return rc;
>>  	}
>>
>>  	rc = tpm_tis_read32(priv, TPM_INT_STATUS(priv->locality), &int_status);
>>  	if (rc < 0) {
>> -		release_locality(chip, priv->locality);
>> +		tpm_tis_release_locality(chip, priv->locality);
>>  		return rc;
>>  	}
>>
>>  	/* Clear all existing */
>>  	rc = tpm_tis_write32(priv, TPM_INT_STATUS(priv->locality), int_status);
>>  	if (rc < 0) {
>> -		release_locality(chip, priv->locality);
>> +		tpm_tis_release_locality(chip, priv->locality);
>>  		return rc;
>>  	}
>>
>> @@ -830,11 +855,11 @@ static int tpm_tis_probe_irq_single(struct tpm_chip *chip, u32 intmask,
>>  	rc = tpm_tis_write32(priv, TPM_INT_ENABLE(priv->locality),
>>  			     intmask | TPM_GLOBAL_INT_ENABLE);
>>  	if (rc < 0) {
>> -		release_locality(chip, priv->locality);
>> +		tpm_tis_release_locality(chip, priv->locality);
>>  		return rc;
>>  	}
>>
>> -	release_locality(chip, priv->locality);
>> +	tpm_tis_release_locality(chip, priv->locality);
>>  	clear_bit(TPM_TIS_IRQ_TESTED, &priv->flags);
>>
>>  	/* Generate an interrupt by having the core call through to
>> @@ -970,8 +995,8 @@ static const struct tpm_class_ops tpm_tis = {
>>  	.req_complete_mask = TPM_STS_DATA_AVAIL | TPM_STS_VALID,
>>  	.req_complete_val = TPM_STS_DATA_AVAIL | TPM_STS_VALID,
>>  	.req_canceled = tpm_tis_req_canceled,
>> -	.request_locality = request_locality,
>> -	.relinquish_locality = release_locality,
>> +	.request_locality = tpm_tis_request_locality,
>> +	.relinquish_locality = tpm_tis_release_locality,
>>  	.clk_enable = tpm_tis_clkrun_enable,
>>  };
>>
>> @@ -1005,6 +1030,8 @@ int tpm_tis_core_init(struct device *dev, struct tpm_tis_data *priv, int irq,
>>  	priv->timeout_min = TPM_TIMEOUT_USECS_MIN;
>>  	priv->timeout_max = TPM_TIMEOUT_USECS_MAX;
>>  	priv->phy_ops = phy_ops;
>> +	priv->locality_count = 0;
>> +	mutex_init(&priv->locality_count_mutex);
>>
>>  	dev_set_drvdata(&chip->dev, priv);
>>
>> @@ -1083,14 +1110,14 @@ int tpm_tis_core_init(struct device *dev, struct tpm_tis_data *priv, int irq,
>>
>>  	intmask &= ~TPM_GLOBAL_INT_ENABLE;
>>
>> -	rc = request_locality(chip, 0);
>> +	rc = tpm_tis_request_locality(chip, 0);
>>  	if (rc < 0) {
>>  		rc = -ENODEV;
>>  		goto out_err;
>>  	}
>>
>>  	tpm_tis_write32(priv, TPM_INT_ENABLE(priv->locality), intmask);
>> -	release_locality(chip, 0);
>> +	tpm_tis_release_locality(chip, 0);
>>
>>  	rc = tpm_chip_start(chip);
>>  	if (rc)
>> @@ -1124,13 +1151,13 @@ int tpm_tis_core_init(struct device *dev, struct tpm_tis_data *priv, int irq,
>>  		 * proper timeouts for the driver.
>>  		 */
>>
>> -		rc = request_locality(chip, 0);
>> +		rc = tpm_tis_request_locality(chip, 0);
>>  		if (rc < 0)
>>  			goto out_err;
>>
>>  		rc = tpm_get_timeouts(chip);
>>
>> -		release_locality(chip, 0);
>> +		tpm_tis_release_locality(chip, 0);
>>
>>  		if (rc) {
>>  			dev_err(dev, "Could not get TPM timeouts and durations\n");
>> @@ -1150,11 +1177,11 @@ int tpm_tis_core_init(struct device *dev, struct tpm_tis_data *priv, int irq,
>>  			dev_err(&chip->dev, FW_BUG
>>  					"TPM interrupt not working, polling instead\n");
>>
>> -			rc = request_locality(chip, 0);
>> +			rc = tpm_tis_request_locality(chip, 0);
>>  			if (rc < 0)
>>  				goto out_err;
>>  			disable_interrupts(chip);
>> -			release_locality(chip, 0);
>> +			tpm_tis_release_locality(chip, 0);
>>  		}
>>  	}
>>
>> @@ -1221,13 +1248,13 @@ int tpm_tis_resume(struct device *dev)
>>  	 * an error code but for unknown reason it isn't handled.
>>  	 */
>>  	if (!(chip->flags & TPM_CHIP_FLAG_TPM2)) {
>> -		ret = request_locality(chip, 0);
>> +		ret = tpm_tis_request_locality(chip, 0);
>>  		if (ret < 0)
>>  			return ret;
>>
>>  		tpm1_do_selftest(chip);
>>
>> -		release_locality(chip, 0);
>> +		tpm_tis_release_locality(chip, 0);
>>  	}
>>
>>  	return 0;
>> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
>> index 2deef11c88db..13bdcf38e56f 100644
>> --- a/drivers/char/tpm/tpm_tis_core.h
>> +++ b/drivers/char/tpm/tpm_tis_core.h
>> @@ -91,6 +91,8 @@ enum tpm_tis_flags {
>>
>>  struct tpm_tis_data {
>>  	u16 manufacturer_id;
>> +	struct mutex locality_count_mutex;
>
> BTW, why mutex and not spinlock?
>
> Hmm.. also I think you might have given feedback already on this
> but could the lock cover the whole struct instead of a counter?
> I tried to dig lore for earlier response but could not find. I'm
> sorry if I'm asking the same question again.
>

Actually thats on me, since it took me much too long to send the v8 after the v7 review.

However the reason that we need a mutex here is that we not only increase or decrease
the locality_counter under the mutex, but also do the locality request and release by
writing to the ACCESS register. Since in the SPI case each communication over the spi bus
is protected by the bus_lock_mutex of the SPI device we must not hold a spinlock when doing
the register accesses.

Concerning covering the whole tpm_tis_data struct:
Most structure elements are set once at driver startup but never changed at driver
runtime. So no locking needed for these. The only exception is "flags" and "locality_count"
whereby "flags" is accessed by atomic bit manipulating functions and thus
does not need extra locking. So "locality_count" is AFAICS the only element that needs to be
protected by the mutex.


> You could probably use rcu for that.
>
>> +	unsigned int locality_count;

Note that we do not only have to increase or decrease the counter atomically, but the first
increment (when the counter goes from 1 to 0) AND requesting the locality by writing to the
ACCESS register has to be atomic.
Likewise the last decrement (when the counter goes from 1 to 0) AND releasing the locality
has to be done atomically:

	mutex_lock(&priv->locality_count_mutex);
	priv->locality_count--;
	if (priv->locality_count == 0)
		tpm_tis_release_locality_locked(priv, l);
	mutex_unlock(&priv->locality_count_mutex);

I dont know if this is possible with RCU, especially since AFAIK RCU works with pointers instead of
integral data types.


Regards,
Lino





>>  	int locality;
>>  	int irq;
>>  	unsigned int int_mask;
>> --
>> 2.36.1
>>
>
> BR, Jarkko