[PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[Johannes Holland]

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@infineon.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

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[Jarkko Sakkinen]

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@infineon.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.

BR, Jarkko

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[James Bottomley]

On Tue, 2022-05-10 at 13:29 +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@infineon.com>

This seems to fix the problem I reported years ago with my Nuvoton
laptop TPM.

https://lore.kernel.org/linux-integrity/1531328689.3260.8.camel@HansenPartnership.com/

It probably needs to soak a bit longer to declare victory (this timeout
failure is very intermittent), but it looks hopeful.

Regards,

James

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[Mimi Zohar]

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@infineon.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

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[James Bottomley]

On Thu, 2022-05-12 at 08:21 -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@infineon.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?

I am:

https://lore.kernel.org/linux-integrity/1531328689.3260.8.camel@HansenPartnership.com/

I'm about 24h into a soak test of the patch with no TPM failure so far.
I think it probably needs to run another 24h just to be sure, but it
does seem the theory is sound (my TPM gets annoyed by being poked too
soon) so reverting 5ef924d9e2e8 looks to be the correct action.  The
only other ways I've found to fix this are either revert the
usleep_range patch altogether or increase the timings:

https://lore.kernel.org/linux-integrity/1531329074.3260.9.camel@HansenPartnership.com/

Which obviously pushes the min past whatever issue my TPM is having
even with 5ef924d9e2e8 applied.

Given that even the commit message for 5ef924d9e2e8 admits it only
shaves about 12% off the TPM response time, that would appear to be an
optimization too far if it's going to cause some TPMs to fail.

James

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[Mimi Zohar]

On Thu, 2022-05-12 at 08:32 -0400, James Bottomley wrote:
> On Thu, 2022-05-12 at 08:21 -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@infineon.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?
> 
> I am:
> 
> https://lore.kernel.org/linux-integrity/1531328689.3260.8.camel@HansenPartnership.com/
> 
> I'm about 24h into a soak test of the patch with no TPM failure so far.
> I think it probably needs to run another 24h just to be sure, but it
> does seem the theory is sound (my TPM gets annoyed by being poked too
> soon) so reverting 5ef924d9e2e8 looks to be the correct action.  The
> only other ways I've found to fix this are either revert the
> usleep_range patch altogether or increase the timings:
> 
> https://lore.kernel.org/linux-integrity/1531329074.3260.9.camel@HansenPartnership.com/
> 
> Which obviously pushes the min past whatever issue my TPM is having
> even with 5ef924d9e2e8 applied.
> 
> Given that even the commit message for 5ef924d9e2e8 admits it only
> shaves about 12% off the TPM response time, that would appear to be an
> optimization too far if it's going to cause some TPMs to fail.

I'd like to understand how pervasive the problem is and which problem
Johannes Holland is trying to address.  Wasn't there already a patch to
limit TPM performance degradation to a single buggy TPM chip already
upstreamed?

thanks,

Mimi

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[Jarkko Sakkinen]

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@infineon.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

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[Jarkko Sakkinen]

On Thu, May 12, 2022 at 08:32:55AM -0400, James Bottomley wrote:
> On Thu, 2022-05-12 at 08:21 -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@infineon.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?
> 
> I am:
> 
> https://lore.kernel.org/linux-integrity/1531328689.3260.8.camel@HansenPartnership.com/
> 
> I'm about 24h into a soak test of the patch with no TPM failure so far.
> I think it probably needs to run another 24h just to be sure, but it
> does seem the theory is sound (my TPM gets annoyed by being poked too
> soon) so reverting 5ef924d9e2e8 looks to be the correct action.  The
> only other ways I've found to fix this are either revert the
> usleep_range patch altogether or increase the timings:
> 
> https://lore.kernel.org/linux-integrity/1531329074.3260.9.camel@HansenPartnership.com/
> 
> Which obviously pushes the min past whatever issue my TPM is having
> even with 5ef924d9e2e8 applied.
> 
> Given that even the commit message for 5ef924d9e2e8 admits it only
> shaves about 12% off the TPM response time, that would appear to be an
> optimization too far if it's going to cause some TPMs to fail.
> 
> James

What if TPM started with the timings as they are now and use the
"reverted" timings if coming up too early?  The question here is
though,  is such complexity worth of anything or should we just
revert and do nothing else.

BR, Jarkko

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[Nayna]

On 5/16/22 13:57, Jarkko Sakkinen wrote:
> On Thu, May 12, 2022 at 08:32:55AM -0400, James Bottomley wrote:
>> On Thu, 2022-05-12 at 08:21 -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@infineon.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?
>> I am:
>>
>> https://lore.kernel.org/linux-integrity/1531328689.3260.8.camel@HansenPartnership.com/
>>
>> I'm about 24h into a soak test of the patch with no TPM failure so far.
>> I think it probably needs to run another 24h just to be sure, but it
>> does seem the theory is sound (my TPM gets annoyed by being poked too
>> soon) so reverting 5ef924d9e2e8 looks to be the correct action.  The
>> only other ways I've found to fix this are either revert the
>> usleep_range patch altogether or increase the timings:
>>
>> https://lore.kernel.org/linux-integrity/1531329074.3260.9.camel@HansenPartnership.com/
>>
>> Which obviously pushes the min past whatever issue my TPM is having
>> even with 5ef924d9e2e8 applied.
>>
>> Given that even the commit message for 5ef924d9e2e8 admits it only
>> shaves about 12% off the TPM response time, that would appear to be an
>> optimization too far if it's going to cause some TPMs to fail.
>>
>> James
> What if TPM started with the timings as they are now and use the
> "reverted" timings if coming up too early?  The question here is
> though,  is such complexity worth of anything or should we just
> revert and do nothing else.

TCG Specification(TCG PC Client Device Driver Design Principles, Section 
10), says - General control timeouts, denoted as TIMEOUT_A (A), 
TIMEOUT_B (B), TIMEOUT_C (C) and TIMEOUT_D (D), are the maximum waiting 
time from a certain control operation from the DD until the TPM shows 
the expected status change.

usleep_range(min, max) takes second parameter as max value which is same 
as maximum delay in our case. Thus the code is in compliance with the 
standard already. We still haven't heard back yet as to the reason for 
this change, nor if the problem is pervasive.

Lastly, a 12% improvement makes a difference or not depends on usecase. 
It did at least in our case.

Thanks & Regards,

      - Nayna

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[James Bottomley]

On Wed, 2022-05-18 at 15:26 -0400, Nayna wrote:
> On 5/16/22 13:57, Jarkko Sakkinen wrote:
> > On Thu, May 12, 2022 at 08:32:55AM -0400, James Bottomley wrote:
> > > On Thu, 2022-05-12 at 08:21 -0400, Mimi Zohar wrote:
[...]
> > > > This patch reverts commit 5ef924d9e2e8 ("tpm: use tpm_msleep()
> > > > value as max delay").    Are you experiencing TPM issues that
> > > > require it?
> > > I am:
> > > 
> > > https://lore.kernel.org/linux-integrity/1531328689.3260.8.camel@HansenPartnership.com/
> > > 
> > > I'm about 24h into a soak test of the patch with no TPM failure
> > > so far.  I think it probably needs to run another 24h just to be
> > > sure, but it does seem the theory is sound (my TPM gets annoyed
> > > by being poked too soon) so reverting 5ef924d9e2e8 looks to be
> > > the correct action.  The only other ways I've found to fix this
> > > are either revert the usleep_range patch altogether or increase
> > > the timings:
> > > 
> > > https://lore.kernel.org/linux-integrity/1531329074.3260.9.camel@HansenPartnership.com/
> > > 
> > > Which obviously pushes the min past whatever issue my TPM is
> > > having even with 5ef924d9e2e8 applied.
> > > 
> > > Given that even the commit message for 5ef924d9e2e8 admits it
> > > only shaves about 12% off the TPM response time, that would
> > > appear to be an optimization too far if it's going to cause some
> > > TPMs to fail.
> > > 
> > > James
> > What if TPM started with the timings as they are now and use the
> > "reverted" timings if coming up too early?  The question here is
> > though,  is such complexity worth of anything or should we just
> > revert and do nothing else.
> 
> TCG Specification(TCG PC Client Device Driver Design Principles,
> Section  10), says - General control timeouts, denoted as TIMEOUT_A
> (A), TIMEOUT_B (B), TIMEOUT_C (C) and TIMEOUT_D (D), are the maximum
> waiting time from a certain control operation from the DD until the
> TPM shows the expected status change.

Actually, this is nothing to do with the TIMEOUTS_A-D: those are the
maximum times before a command should complete.  This is the minimum
time we should wait between pokes of the TPM to see if it is ready. 
Usually the use case is:

while (read device status gives not ready)
   tpm_msleep(something)

The tpm_msleep gives up CPU control (to prevent huge amounts of busy
waiting) but before 424eaf910c32 ("tpm: reduce polling time to usecs
for even finer granularity") we would sleep for an entire tick (time
taken to make the process runnable) before the next poll, and since
most TPM commands don't return immediately, that was a gate on how fast
you could do simple TPM operations (like PCR extend).

As far as I know, no TCG spec gives any details of the minimum wait
time between poll cycles, so this is really something the manufacturer
has to tell us.

Just for completeness, my soak test did run to completion, but my TPM
has since failed and dropped off the bus, so simply reverting this
patch (5ef924d9e2e8) isn't sufficient to fully fix my problem.

James

Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[Ken Goldman]

[-- Attachment #1: Type: text/plain, Size: 1494 bytes --]

On 5/18/2022 4:21 PM, James Bottomley wrote:
> Actually, this is nothing to do with the TIMEOUTS_A-D: those are the
> maximum times before a command should complete.  This is the minimum
> time we should wait between pokes of the TPM to see if it is ready.
> Usually the use case is:
> 
> while (read device status gives not ready)
>     tpm_msleep(something)
> 
> The tpm_msleep gives up CPU control (to prevent huge amounts of busy
> waiting) but before 424eaf910c32 ("tpm: reduce polling time to usecs
> for even finer granularity") we would sleep for an entire tick (time
> taken to make the process runnable) before the next poll, and since
> most TPM commands don't return immediately, that was a gate on how fast
> you could do simple TPM operations (like PCR extend).
> 
> As far as I know, no TCG spec gives any details of the minimum wait
> time between poll cycles, so this is really something the manufacturer
> has to tell us.
> 
> Just for completeness, my soak test did run to completion, but my TPM
> has since failed and dropped off the bus, so simply reverting this
> patch (5ef924d9e2e8) isn't sufficient to fully fix my problem.

[FYI]

The TPM vendors explained that polling interrupts TPM command
processing. This will make commands take longer.

They recommend adaptive sleep time based on (at least) the
command.  E.g., getcapability, pcrread, ... are fast so a short
sleep is appropriate.  create, createprimary are slow so
a longer sleep will have better performance.

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Re: [PATCH] tpm: sleep at least <...> ms in tpm_msleep()

[Stefan Mahnke-Hartmann]

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@infineon.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