linux-kernel - Re: [PATCH] tpm: sleep at least <...> ms in tpm

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Date:   Mon, 20 Jun 2022 17:58:07 +0200
From:   Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>
CC:     Johannes Holland <johannes.holland@...ineon.com>,
        Nayna <nayna@...ux.vnet.ibm.com>,
        <linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <peterhuewe@....de>, <jgg@...pe.ca>,
        <stefan.mahnke-hartmann@...ineon.com>
Subject: Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()



On 16.05.22 19:54, Jarkko Sakkinen wrote:
> On Thu, May 12, 2022 at 08:21:17AM -0400, Mimi Zohar wrote:
>> On Wed, 2022-05-11 at 18:16 +0300, Jarkko Sakkinen wrote:
>>> On Tue, May 10, 2022 at 01:29:03PM +0200, Johannes Holland wrote:
>>>> To comply with protocol requirements, minimum polling times must often
>>>> be adhered to. Therefore, a macro like tpm_msleep() should sleep at
>>>> least the given amount of time (not up to the given period). Have
>>>> tpm_msleep() sleep at least the given number of milliseconds.
>>>>
>>>> Signed-off-by: Johannes Holland <johannes.holland@...ineon.com>
>>>> ---
>>>>  drivers/char/tpm/tpm.h | 4 ++--
>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
>>>> index 2163c6ee0d36..0971b55fffe3 100644
>>>> --- a/drivers/char/tpm/tpm.h
>>>> +++ b/drivers/char/tpm/tpm.h
>>>> @@ -185,8 +185,8 @@ int tpm_pm_resume(struct device *dev);
>>>>  
>>>>  static inline void tpm_msleep(unsigned int delay_msec)
>>>>  {
>>>> -	usleep_range((delay_msec * 1000) - TPM_TIMEOUT_RANGE_US,
>>>> -		     delay_msec * 1000);
>>>> +	usleep_range(delay_msec * 1000, (delay_msec * 1000)
>>>> +		     + TPM_TIMEOUT_RANGE_US);
>>>>  };
>>>>  
>>>>  int tpm_chip_start(struct tpm_chip *chip);
>>>> -- 
>>>> 2.34.1
>>>>
>>> For this I would really like to hear a 2nd opinion from Nayna and Mimi.
>> This patch reverts commit 5ef924d9e2e8 ("tpm: use tpm_msleep() value as
>> max delay").    Are you experiencing TPM issues that require it?
>>
>> thanks,
>>
>> Mimi
> Yeah, there's no data to support making anything.  Without a live
> system having issues with this, I guess this quite definitive NAK.
>
> BR, Jarkko
>
Either way, a static range is not perfect. So I would suggest,to have the
values (TPM_TIMEOUT_RANGE_US, TPM_TIMEOUT_POLL) settable, to give the
possibility to adjust the polling timing vendor specific. Furthermore,
increasing the polling delay as a function of time would limit the number
of attempts, especially for long-running commands.

BR, Stefan