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

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Date:   Wed, 20 Apr 2022 08:32:19 +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
Subject: Re: [PATCH v3 0/4] Fixes for TPM interrupt handling

On Wed, 2022-04-20 at 08:30 +0300, 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.
> 
> # [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.
> 
> 
> # [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.

I.e. to move forward create first localized fixes, and only after those
clean ups if there is point. Removing code (like in 2/4) is not a bug
fix fo anything. This not to say that some changes would be illegit, I'm
only saying that the patches are badly scoped.

BR, Jarkko