Re: TPM operation times out (very rarely)

[Jarkko Sakkinen <jarkko@kernel.org>]

On Mon, Feb 24, 2025 at 01:56:56PM +0100, Michal Suchánek wrote:
> On Wed, Feb 19, 2025 at 10:29:45PM +0000, Jonathan McDowell wrote:
> > On Wed, Jan 29, 2025 at 04:27:15PM +0100, Michal Suchánek wrote:
> > > Hello,
> > > 
> > > there is a problem report that booting a specific type of system about
> > > 0.1% of the time encrypted volume (using a PCR to release the key) fails
> > > to unlock because of TPM operation timeout.
> > > 
> > > Minimizing the test case failed so far.
> > > 
> > > For example, booting into text mode as opposed to graphical desktop
> > > makes the problem unreproducible.
> > > 
> > > The test is done with a frankenkernel that has TPM drivers about on par
> > > with Linux 6.4 but using actual Linux 6.4 the problem is not
> > > reproducible, either.
> > > 
> > > However, given the problem takes up to a day to reproduce I do not have
> > > much confidence in the negative results.
> > 
> > Michal, can you possibly try the below and see if it helps out? There
> > seems to be a timing bug introduced in 6.4+ that I think might be
> > related, and matches up with some of our internal metrics that showed an
> > increase in timeouts in 6.4 onwards.
> > 
> > commit 79041fba797d0fe907e227012767f56dd93fac32
> > Author: Jonathan McDowell <noodles@meta.com>
> > Date:   Wed Feb 19 16:20:44 2025 -0600
> > 
> >     tpm, tpm_tis: Fix timeout handling when waiting for TPM status
> >     
> >     The change to only use interrupts to handle supported status changes,
> >     then switch to polling for the rest, inverted the status test and sleep
> >     such that we can end up sleeping beyond our timeout and not actually
> >     checking the status. This can result in spurious TPM timeouts,
> >     especially on a more loaded system. Fix by switching the order back so
> >     we sleep *then* check. We've done a up front check when we enter the
> >     function so this won't cause an additional delay when the status is
> >     already what we're looking for.
> >     
> >     Cc: stable@vger.kernel.org # v6.4+
> >     Fixes: e87fcf0dc2b4 ("tpm, tpm_tis: Only handle supported interrupts")
> >     Signed-off-by: Jonathan McDowell <noodles@meta.com>
> 
> Reviewed-by: Michal Suchánek <msuchanek@suse.de>

Send as a proper patch. I've this month mostly on holiday but will be
back at work on Monday.

BR, Jarkko