linux-kernel - [PATCH v2] tpm, tpm_tis: Fix timeout handling when waiting for TPM status

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Message-ID: <Z87ZcPZvoUXZ7M_f@earth.li>
Date: Mon, 10 Mar 2025 12:22:08 +0000
From: Jonathan McDowell <noodles@...th.li>
To: Jarkko Sakkinen <jarkko@...nel.org>, Peter Huewe <peterhuewe@....de>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Lino Sanfilippo <l.sanfilippo@...bus.com>,
	Michal Suchánek <msuchanek@...e.de>
Cc: linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] tpm, tpm_tis: Fix timeout handling when waiting for TPM
 status

The change to only use interrupts to handle supported status changes
introduced an issue when it is necessary to poll for the status. Rather
than checking for the status after sleeping the code now sleeps after
the check. This means a correct, but slower, status change on the part
of the TPM can be missed, resulting in a spurious timeout error,
especially on a more loaded system. Switch back to sleeping *then*
checking. An up front check of the status has been done at the start of
the function, so this does not cause an additional delay when the status
is already what we're looking for.

Cc: stable@...r.kernel.org # v6.4+
Fixes: e87fcf0dc2b4 ("tpm, tpm_tis: Only handle supported interrupts")
Signed-off-by: Jonathan McDowell <noodles@...a.com>
Reviewed-by: Michal Suchánek <msuchanek@...e.de>
Reviewed-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
---
v2: Reword commit message
     Don't needlessly wrap line

  drivers/char/tpm/tpm_tis_core.c | 3 +--
  1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index fdef214b9f6b..c969a1793184 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -114,11 +114,10 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
  		return 0;
  	/* process status changes without irq support */
  	do {
+		usleep_range(priv->timeout_min, priv->timeout_max);
  		status = chip->ops->status(chip);
  		if ((status & mask) == mask)
  			return 0;
-		usleep_range(priv->timeout_min,
-			     priv->timeout_max);
  	} while (time_before(jiffies, stop));
  	return -ETIME;
  }
-- 
2.48.1