Re: [PATCH v4 4/6] tpm, tpm_tis: avoid CPU cache incoherency in irq test

[Jarkko Sakkinen]

On Mon, May 09, 2022 at 10:05:57AM +0200, Lino Sanfilippo wrote:
> From: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
> 
> The interrupt handler that sets irq_tested to indicate that interrupts are
> working may run on another CPU than the thread that checks this variable in
> tmp_tis_send().
> 
> Since no synchronization is used to access irq_tested, there is no
> guarantee for cache coherency between the CPUs, so that the value set by
> the interrupt handler might not be visible to the testing thread.
> 
> Avoid this issue by using a bitfield instead of a boolean variable and by
> accessing this field with bit manipulating functions that guarantee cache
> coherency.
> 
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
> ---
>  drivers/char/tpm/tpm_tis_core.c | 13 +++++++------
>  drivers/char/tpm/tpm_tis_core.h |  6 +++++-
>  2 files changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 4f3b82c3f205..bdfde1cd71fe 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -470,7 +470,8 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
>  	int rc, irq;
>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>  
> -	if (!(chip->flags & TPM_CHIP_FLAG_IRQ) || priv->irq_tested)
> +	if (!(chip->flags & TPM_CHIP_FLAG_IRQ) ||
> +	     test_bit(TPM_TIS_IRQTEST_OK, &priv->irqtest_flags))
>  		return tpm_tis_send_main(chip, buf, len);
>  
>  	/* Verify receipt of the expected IRQ */
> @@ -480,11 +481,11 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
>  	rc = tpm_tis_send_main(chip, buf, len);
>  	priv->irq = irq;
>  	chip->flags |= TPM_CHIP_FLAG_IRQ;
> -	if (!priv->irq_tested)
> +	if (!test_bit(TPM_TIS_IRQTEST_OK, &priv->irqtest_flags))
>  		tpm_msleep(1);
> -	if (!priv->irq_tested)
> +	if (!test_bit(TPM_TIS_IRQTEST_OK, &priv->irqtest_flags))
>  		disable_interrupts(chip);
> -	priv->irq_tested = true;
> +	set_bit(TPM_TIS_IRQTEST_OK, &priv->irqtest_flags);
>  	return rc;
>  }
>  
> @@ -689,7 +690,7 @@ static irqreturn_t tis_int_handler(int dummy, void *dev_id)
>  	if (interrupt == 0)
>  		return IRQ_NONE;
>  
> -	priv->irq_tested = true;
> +	set_bit(TPM_TIS_IRQTEST_OK, &priv->irqtest_flags);
>  	if (interrupt & TPM_INTF_DATA_AVAIL_INT)
>  		wake_up_interruptible(&priv->read_queue);
>  	if (interrupt & TPM_INTF_LOCALITY_CHANGE_INT)
> @@ -780,7 +781,7 @@ static int tpm_tis_probe_irq_single(struct tpm_chip *chip, u32 intmask,
>  	if (rc < 0)
>  		return rc;
>  
> -	priv->irq_tested = false;
> +	clear_bit(TPM_TIS_IRQTEST_OK, &priv->irqtest_flags);
>  	chip->flags |= TPM_CHIP_FLAG_IRQ;
>  
>  	/* Generate an interrupt by having the core call through to
> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
> index 43b724e55192..c8972ea8e13e 100644
> --- a/drivers/char/tpm/tpm_tis_core.h
> +++ b/drivers/char/tpm/tpm_tis_core.h
> @@ -89,11 +89,15 @@ enum tpm_tis_flags {
>  	TPM_TIS_USE_THREADED_IRQ	= BIT(2),
>  };
>  
> +enum tpm_tis_irqtest_flags {
> +	TPM_TIS_IRQTEST_OK		= BIT(0),
> +};
> +
>  struct tpm_tis_data {
>  	u16 manufacturer_id;
>  	int locality;
>  	int irq;
> -	bool irq_tested;
> +	unsigned long irqtest_flags;
>  	unsigned long flags;
>  	void __iomem *ilb_base_addr;
>  	u16 clkrun_enabled;
> -- 
> 2.36.0
> 

So, this would caused by changing to threaded IRQs?

BR, Jarkko