linux-kernel - Re: [PATCH v3 0/4] Fixes for TPM interrupt handling

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Date:   Fri, 25 Mar 2022 13:32:25 +0100
From:   Michael Niewöhner <linux@...ewoehner.de>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Lino Sanfilippo <LinoSanfilippo@....de>, peterhuewe@....de,
        jgg@...pe.ca, stefanb@...ux.vnet.ibm.com, stefanb@...ux.ibm.com,
        James.Bottomley@...senpartnership.com, keescook@...omium.org,
        jsnitsel@...hat.com, ml.linux@...oe.vision,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        twawrzynczak@...omium.org
Subject: Re: [PATCH v3 0/4] Fixes for TPM interrupt handling

On Fri, 2022-03-25 at 04:14 +0200, Jarkko Sakkinen wrote:
> On Thu, Mar 24, 2022 at 06:04:23PM +0100, Michael Niewöhner wrote:
> > Hi guys,
> > 
> > On Thu, 2021-05-06 at 04:47 +0300, Jarkko Sakkinen wrote:
> > > On Wed, May 05, 2021 at 01:15:29AM +0200, Lino Sanfilippo wrote:
> > > > Hi,
> > > > 
> > > > On 03.05.21 at 17:50, Jarkko Sakkinen wrote:
> > > > > What the heck is "simplification" and what that has to do with fixing
> > > > > anything? I don't understand your terminology.
> > > > 
> > > > 
> > > > The intention for this patch is not to fix anything. Please read the
> > > > cover
> > > > letter and the commit message.
> > > > This patch is about making the locality handling easier by not
> > > > claiming/releasing
> > > > it multiple times over the driver life time, but claiming it once at
> > > > driver
> > > > startup and only releasing it at driver shutdown.
> > > > 
> > > > Right now we have locality request/release combos in
> > > > 
> > > > - probe_itpm()
> > > > - tpm_tis_gen_interrupt()
> > > > - tpm_tis_core_init()
> > > > - tpm_chip_start()
> > > > 
> > > > and there is still one combo missing for
> > > > 
> > > > - tpm2_get_timeouts()
> > > > 
> > > > which is the reason why we get the "TPM returned invalid status" bug in
> > > > case
> > > > of TPM2 (and this is the bug which is _incidentally_ fixed by this
> > > > patch,
> > > > see
> > > > below).
> > > > 
> > > > And if we are going to enable interrupts, we have to introduce yet
> > > > another
> > > > combo,
> > > > for accessing the status register in the interrupt handler, since TPM
> > > > 2.0
> > > > requires holding the locality for writing to the status register. That
> > > > makes
> > > > 6 different code places in which we take and release the locality.
> > > > 
> > > > With this patch applied we only take the locality at one place.
> > > > Furthermore
> > > > with interrupts enabled we dont have to claim the locality for each
> > > > handler
> > > > execution, saving us countless claim/release combinations at runtime.
> > > > 
> > > > Hence the term "simplification" which is perfectly justified IMO.
> > > > 
> > > > So again, this patch is "only" in preparation for the next patch when
> > > > interrupts
> > > > are actually enabled and we would have to take the locality in the
> > > > interrupt
> > > > handler without this patch.
> > > 
> > > So: what problem this patch does solve?
> > > 
> > > /Jarkko
> > > 
> > 
> > first, thank you very much, Lino, for working on this! I've been debugging
> > issues with the tis driver in the last days and was about to start with the
> > same
> > approach as yours when I luckily discovered your patch!
> > 
> > Jarkko, while I agree, that the commit message is not optimal, Lino tried
> > hard
> > to explain what the problems with the current code are and how they are /
> > can be
> > fixed. Further, I too don't see why simplification / optimization is such a
> > bad
> > thing. This driver is actually a very good example. I had a hard time, too,
> > figuring out what's going on there. A clean rewrite is a very valid approach
> > here IMO. It's not "polishing for nothing", as you described it, but
> > actually
> > solving problems.
> > 
> > Interrupt detection is broken for years now and finally a volunteer worked
> > on a
> > solution. Don't you think this should be valued? Let's get this problem
> > sorted
> > out :-)
> > 
> > Lino, I'd be happy to test the patches, when you have time and interest to
> > work
> > on this again!
> > 
> > Thanks, Michael
> 
> It's quite easy to test them out. Both fixes are in the mainline GIT tree.
> E.g. give a shot rc1, and please report if any issues persists to:
> 
>   linux-integrity@...r.kernel.org 
> 
> BR, Jarkko

I don't see Linos patches on mainline. Also, the series included four patches:
[PATCH v3 0/4] Fixes for TPM interrupt handling
[PATCH v3 1/4] tpm: Use a threaded interrupt handler
[PATCH v3 2/4] tpm: Simplify locality handling
[PATCH v3 3/4] tpm: Fix test for interrupts
[PATCH v3 4/4] tpm: Only enable supported irqs

Three of them are relevant for the interrupt problem, which is still present in
mainline, as these patches were refused:
[PATCH v3 1/4] tpm: Use a threaded interrupt handler
[PATCH v3 2/4] tpm: Simplify locality handling
[PATCH v3 3/4] tpm: Fix test for interrupts

Michael