Re: [PATCH v2 2/5] tpm_tis: Clean up locality release

[Jerry Snitselaar <jsnitsel@redhat.com>]

James Bottomley @ 2020-10-01 11:09 MST:

> The current release locality code seems to be based on the
> misunderstanding that the TPM interrupts when a locality is released:
> it doesn't, only when the locality is acquired.
>
> Furthermore, there seems to be no point in waiting for the locality to
> be released.  All it does is penalize the last TPM user.  However, if
> there's no next TPM user, this is a pointless wait and if there is a
> next TPM user, they'll pay the penalty waiting for the new locality
> (or possibly not if it's the same as the old locality).
>
> Fix the code by making release_locality as simple write to release
> with no waiting for completion.
>
> Fixes: 33bafe90824b ("tpm_tis: verify locality released before returning from release_locality")
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
>
> ---
>
> v2: added fixes
> ---
>  drivers/char/tpm/tpm_tis_core.c | 47 +--------------------------------
>  1 file changed, 1 insertion(+), 46 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index f3ecde8df47d..431919d5f48a 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -135,58 +135,13 @@ static bool check_locality(struct tpm_chip *chip, int l)
>  	return false;
>  }
>  
> -static bool locality_inactive(struct tpm_chip *chip, int l)
> -{
> -	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> -	int rc;
> -	u8 access;
> -
> -	rc = tpm_tis_read8(priv, TPM_ACCESS(l), &access);
> -	if (rc < 0)
> -		return false;
> -
> -	if ((access & (TPM_ACCESS_VALID | TPM_ACCESS_ACTIVE_LOCALITY))
> -	    == TPM_ACCESS_VALID)
> -		return true;
> -
> -	return false;
> -}
> -
>  static int release_locality(struct tpm_chip *chip, int l)
>  {
>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> -	unsigned long stop, timeout;
> -	long rc;
>  
>  	tpm_tis_write8(priv, TPM_ACCESS(l), TPM_ACCESS_ACTIVE_LOCALITY);
>  
> -	stop = jiffies + chip->timeout_a;
> -
> -	if (chip->flags & TPM_CHIP_FLAG_IRQ) {
> -again:
> -		timeout = stop - jiffies;
> -		if ((long)timeout <= 0)
> -			return -1;
> -
> -		rc = wait_event_interruptible_timeout(priv->int_queue,
> -						      (locality_inactive(chip, l)),
> -						      timeout);
> -
> -		if (rc > 0)
> -			return 0;
> -
> -		if (rc == -ERESTARTSYS && freezing(current)) {
> -			clear_thread_flag(TIF_SIGPENDING);
> -			goto again;
> -		}
> -	} else {
> -		do {
> -			if (locality_inactive(chip, l))
> -				return 0;
> -			tpm_msleep(TPM_TIMEOUT);
> -		} while (time_before(jiffies, stop));
> -	}
> -	return -1;
> +	return 0;
>  }
>  
>  static int request_locality(struct tpm_chip *chip, int l)

Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>