linux-kernel - Re: [PATCH v5 07/10] tmp, tmp_tis: Implement usage counter for locality

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Date:   Wed, 15 Jun 2022 21:23:18 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     LinoSanfilippo@....de
Cc:     peterhuewe@....de, jgg@...pe.ca, stefanb@...ux.vnet.ibm.com,
        linux@...ewoehner.de, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, l.sanfilippo@...bus.com,
        lukas@...ner.de, p.rosenberger@...bus.com
Subject: Re: [PATCH v5 07/10] tmp, tmp_tis: Implement usage counter for
 locality

On Fri, Jun 10, 2022 at 01:08:43PM +0200, LinoSanfilippo@....de wrote:
> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
> 
> 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.
> 
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
> ---
>  drivers/char/tpm/tpm_tis_core.c | 30 ++++++++++++++++++++++++++++--
>  drivers/char/tpm/tpm_tis_core.h |  2 ++
>  2 files changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 028bec44362d..0ef74979bc2c 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -158,16 +158,26 @@ static bool check_locality(struct tpm_chip *chip, int l)
>  	return false;
>  }
>  
> +static int release_locality_locked(struct tpm_tis_data *priv, int l)
> +{
> +	tpm_tis_write8(priv, TPM_ACCESS(l), TPM_ACCESS_ACTIVE_LOCALITY);

nit: empty line here

Also it would not hurt to prefix it with tpm_tis.

This is for simple and practical reasons, like grepping. I don't
mind if you do that also for other functions (if you want to).

> +	return 0;
> +}
> +
>  static int 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)
> +		release_locality_locked(priv, l);
> +	mutex_unlock(&priv->locality_count_mutex);
>  
>  	return 0;
>  }
>  
> -static int request_locality(struct tpm_chip *chip, int l)
> +static int request_locality_locked(struct tpm_chip *chip, int l)
>  {
>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>  	unsigned long stop, timeout;
> @@ -208,6 +218,20 @@ static int request_locality(struct tpm_chip *chip, int l)
>  	return -1;
>  }
>  
> +static int 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 = 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);
> @@ -987,6 +1011,8 @@ 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);
>  
> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
> index 8e02faa4079d..e1871c482da2 100644
> --- a/drivers/char/tpm/tpm_tis_core.h
> +++ b/drivers/char/tpm/tpm_tis_core.h
> @@ -94,6 +94,8 @@ enum tpm_tis_irqtest_flags {
>  
>  struct tpm_tis_data {
>  	u16 manufacturer_id;
> +	struct mutex locality_count_mutex;
> +	unsigned int locality_count;
>  	int locality;
>  	int irq;
>  	unsigned int irqs_in_use;
> -- 
> 2.36.1
> 

BR, Jarkko