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

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Date:   Mon, 25 Apr 2022 16:57:51 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Lino Sanfilippo <LinoSanfilippo@....de>,
        Michael Niewöhner <linux@...ewoehner.de>
Cc:     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, Lukas Wunner <lukas@...ner.de>,
        Philipp Rosenberger <p.rosenberger@...bus.com>
Subject: Re: [PATCH v3 0/4] Fixes for TPM interrupt handling

On Sun, 2022-04-24 at 04:22 +0200, Lino Sanfilippo wrote:
> 
> Hi,
> 
> On 20.04.22 at 07:30, Jarkko Sakkinen wrote:
> > n Sat, 2022-03-26 at 04:24 +0100, Lino Sanfilippo wrote:
> > > 
> > > Hi Michael,
> > > 
> > > On 25.03.22 at 13:32, Michael Niewöhner wrote:
> > > > > > 
> > > > > > 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
> > > > 
> > > 
> > > You are right, the interrupts are still not working in the mainline kernel.
> > > I would gladly make another attempt to fix this but rather step by step
> > > than in a series that tries to fix (different) things at once.
> > > 
> > > A first step could be to have a sleepable context for the interrupt handling,
> > > since in case of SPI the accesses to the irq status register may sleep.
> > > 
> > > I sent a patch for this purpose once, but it seems to have gone lost:
> > > 
> > > https://lore.kernel.org/all/20210620023444.14684-1-LinoSanfilippo@gmx.de/
> > > 
> > > 
> > > Best regards,
> > > Lino
> > 
> > I went these through one by one>
> > # Above linked patch
> > 
> > Boolean parameters are considered bad. I.e. use named flags
> > instead. This is for above linked patch.
> 
> Ok, we could extend tpm_tis_flags by a flag "TPM_TIS_USE_THREADED_IRQ"
> for this.
> 
> > 
> > # [PATCH v3 3/4] tpm: Fix test for interrupts
> > 
> > 1. Please remove "unnecessarily complicated" sentence because
> >    it cannot be evaluated. It's your opinion, which might perhaps
> >    be correct, but it is irrelevant for any possible patch
> >    description.
> > 2. There's no such thing as "fix by re-implementation". Please
> >    explain instead code change is relevant for the bug fix.
> > 3. If set_bit() et al necessarily to fix a possible race condition
> >    you need to have a separate patch for that.
> > 
> > To move forward, start with a better summary such as
> > 
> > "tpm: move interrupt test to tpm_tis_probe_irq_single()"
> > 
> > I'd also either revert the change for flags, or alternatively
> > move it to separate patch explaining race condition. Otherwise,
> > there's no argument of saying that using set_bit() is more
> > proper. This will make the change more localized.
> > 
> 
> Ok, I will split the fix for the irq test into two patches then.
> 
> > 
> > # [PATCH v3 2/4] tpm: Simplify locality handling
> > 
> > "As a side-effect these modifications fix a bug which results in the
> > following warning when using TPM 2:"
> > 
> > Generally speaking, the simplifications should be done on top of code
> > that does not have known bugs, even if the simplification renders out
> > the bug. This is because then we have code that have potentially unknown
> > unknown bugs.
> > 
> > I hope you see my point. The problem with these patches were then
> > and is still that they intermix bug fixes and other modifications and
> > thus cannot be taken in.
> > 
> 
> Yes, I can see that point.
> 
> > BR, Jarkko
> > 
> 
> Thanks a lot for the review. I will prepare new patches with the suggested
> changes.

Yeah, I mean the point being: it's OK to suggest clean ups but with bug fixes
you should aim for the lowest common denominator as far as you possibly can.

BR, Jarkko