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

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Message-ID: <bda377bf-10f8-49d9-8e58-ec957a40e4d7@gmail.com>
Date: Fri, 20 Jun 2025 18:19:43 +0100
From: "Orlov, Ivan" <ivan.orlov0322@...il.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, "Orlov, Ivan" <iorlov@...zon.co.uk>
Cc: "peterhuewe@....de" <peterhuewe@....de>, "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 11/06/2025 18:02, Jarkko Sakkinen wrote:
>> Instead, perform the check in the following way:
>>
>> 1. Read the current timestamp
>> 2. Read the completion status. If completed, return the result
>> 3. Sleep
>> 4. Check if the timestamp read at step 1 exceeds the timeout. Return
>>     an error if it does
>> 5. Goto 1
>>
>> Also, use ktime instead of jiffes as a more reliable and precise timing
>> source.
> 
> "also", i.e. a logically separate change which should be split up to
> a separate patch.
> 

Got it, will send this enhancement as a separate patch.

>> +		curr_time = ktime_get();
>>   		u8 status = tpm_chip_status(chip);
>>   		if ((status & chip->ops->req_complete_mask) ==
>>   		    chip->ops->req_complete_val)
>> @@ -140,7 +149,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
>>   
>>   		tpm_msleep(TPM_TIMEOUT_POLL);
>>   		rmb();
>> -	} while (time_before(jiffies, stop));
>> +	} while (ktime_before(curr_time, timeout));
> 
> 
> Wouldn't it be simpler fix to just check completion after dropping out
> of the loop?
> 

yes, this should also solve the problem without taking additional space 
on the stack with new vars. Will update in V2, thanks!

> And declare this before tpm_try_transmit():
> 
> static bool tpm_transmit_completed(struct tpm_chip *chip)
> {
> 	u8 status = tpm_chip_status(chip);
> 	
> 	return (status & chip->ops->req_complete_mask) == chip->ops->req_complete_val;
> }
> 

Cool, will do.

Thanks for the review and sorry for the late reply.

--
Kind regards,
Ivan Orlov