linux-kernel - Re: [PATCH] tpm: Fix the timeout & use ktime

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Message-ID: <8112fd6c-4be7-4d61-9d5e-372e2499cdea@gmail.com>
Date: Fri, 20 Jun 2025 18:23:23 +0100
From: "Orlov, Ivan" <ivan.orlov0322@...il.com>
To: Jonathan McDowell <noodles@...th.li>, "Orlov, Ivan" <iorlov@...zon.co.uk>
Cc: "peterhuewe@....de" <peterhuewe@....de>,
 "jarkko@...nel.org" <jarkko@...nel.org>, "jgg@...pe.ca" <jgg@...pe.ca>,
 "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "Woodhouse, David" <dwmw@...zon.co.uk>
Subject: Re: [PATCH] tpm: Fix the timeout & use ktime

On 20/06/2025 14:24, Jonathan McDowell wrote:
> This looks similar to the issue I fixed in 7146dffa875c ('Fix timeout
> handling when waiting for TPM status'), I assume you're actually seeing
> it in your systems? I think we're starting to see it (rarely) now the
> other issues are fixed in our builds. As a similar approach does the
> following work?
> 
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm- 
> interface.c
> index 8d7e4da6ed53..18ae0767fa60 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -127,7 +127,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip 
> *chip, void *buf, size_t bufsiz)
>           goto out_recv;
> 
>       stop = jiffies + tpm_calc_ordinal_duration(chip, ordinal);
> -    do {
> +    while (true) {
>           u8 status = tpm_chip_status(chip);
>           if ((status & chip->ops->req_complete_mask) ==
>               chip->ops->req_complete_val)
> @@ -138,9 +138,12 @@ static ssize_t tpm_try_transmit(struct tpm_chip 
> *chip, void *buf, size_t bufsiz)
>               return -ECANCELED;
>           }
> 

<-- This would solve the problem with usleep_range taking arbitrary 
time, but unfortunately won't solve it for the guest VM scenario: if 
vCPU gets interrupted here, then it still will account the steal time 
and time out when it's woken up before checking for completion again

> +        if (time_after(jiffies, stop))
> +            break;
> +
>           tpm_msleep(TPM_TIMEOUT_POLL);
>           rmb();
> -    } while (time_before(jiffies, stop));
> +    }
> 
>       tpm_chip_cancel(chip);
>       dev_err(&chip->dev, "Operation Timed out\n");

--
Kind regards,
Ivan Orlov