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Date:   Sun, 29 Nov 2020 05:23:06 +0200
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Hans de Goede <hdegoede@redhat.com>
Cc:     Jerry Snitselaar <jsnitsel@redhat.com>,
        Matthew Garrett <mjg59@google.com>,
        linux-integrity <linux-integrity@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Huewe <peterhuewe@gmx.de>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [PATCH] tpm_tis: Disable interrupts on ThinkPad T490s
Message-ID: <20201129032306.GD39488@kernel.org>
References: <20201015214430.17937-1-jsnitsel@redhat.com>
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On Tue, Nov 24, 2020 at 10:45:01PM +0100, Hans de Goede wrote:
> Hi,
> 
> On 11/24/20 6:52 PM, Jerry Snitselaar wrote:
> > 
> > Jarkko Sakkinen @ 2020-11-23 20:26 MST:
> > 
> >> On Wed, Nov 18, 2020 at 11:36:20PM -0700, Jerry Snitselaar wrote:
> >>>
> >>> Matthew Garrett @ 2020-10-15 15:39 MST:
> >>>
> >>>> On Thu, Oct 15, 2020 at 2:44 PM Jerry Snitselaar <jsnitsel@redhat.com> wrote:
> >>>>>
> >>>>> There is a misconfiguration in the bios of the gpio pin used for the
> >>>>> interrupt in the T490s. When interrupts are enabled in the tpm_tis
> >>>>> driver code this results in an interrupt storm. This was initially
> >>>>> reported when we attempted to enable the interrupt code in the tpm_tis
> >>>>> driver, which previously wasn't setting a flag to enable it. Due to
> >>>>> the reports of the interrupt storm that code was reverted and we went back
> >>>>> to polling instead of using interrupts. Now that we know the T490s problem
> >>>>> is a firmware issue, add code to check if the system is a T490s and
> >>>>> disable interrupts if that is the case. This will allow us to enable
> >>>>> interrupts for everyone else. If the user has a fixed bios they can
> >>>>> force the enabling of interrupts with tpm_tis.interrupts=1 on the
> >>>>> kernel command line.
> >>>>
> >>>> I think an implication of this is that systems haven't been
> >>>> well-tested with interrupts enabled. In general when we've found a
> >>>> firmware issue in one place it ends up happening elsewhere as well, so
> >>>> it wouldn't surprise me if there are other machines that will also be
> >>>> unhappy with interrupts enabled. Would it be possible to automatically
> >>>> detect this case (eg, if we get more than a certain number of
> >>>> interrupts in a certain timeframe immediately after enabling the
> >>>> interrupt) and automatically fall back to polling in that case? It
> >>>> would also mean that users with fixed firmware wouldn't need to pass a
> >>>> parameter.
> >>>
> >>> I believe Matthew is correct here. I found another system today
> >>> with completely different vendor for both the system and the tpm chip.
> >>> In addition another Lenovo model, the L490, has the issue.
> >>>
> >>> This initial attempt at a solution like Matthew suggested works on
> >>> the system I found today, but I imagine it is all sorts of wrong.
> >>> In the 2 systems where I've seen it, there are about 100000 interrupts
> >>> in around 1.5 seconds, and then the irq code shuts down the interrupt
> >>> because they aren't being handled.
> >>>
> >>>
> >>> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> >>> index 49ae09ac604f..478e9d02a3fa 100644
> >>> --- a/drivers/char/tpm/tpm_tis_core.c
> >>> +++ b/drivers/char/tpm/tpm_tis_core.c
> >>> @@ -27,6 +27,11 @@
> >>>  #include "tpm.h"
> >>>  #include "tpm_tis_core.h"
> >>>
> >>> +static unsigned int time_start = 0;
> >>> +static bool storm_check = true;
> >>> +static bool storm_killed = false;
> >>> +static u32 irqs_fired = 0;
> >>
> >> Maybe kstat_irqs() would be a better idea than ad hoc stats.
> >>
> > 
> > Thanks, yes that would be better.
> > 
> >>> +
> >>>  static void tpm_tis_clkrun_enable(struct tpm_chip *chip, bool value);
> >>>
> >>>  static void tpm_tis_enable_interrupt(struct tpm_chip *chip, u8 mask)
> >>> @@ -464,25 +469,31 @@ static int tpm_tis_send_data(struct tpm_chip *chip, const u8 *buf, size_t len)
> >>>         return rc;
> >>>  }
> >>>
> >>> -static void disable_interrupts(struct tpm_chip *chip)
> >>> +static void __disable_interrupts(struct tpm_chip *chip)
> >>>  {
> >>>         struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> >>>         u32 intmask;
> >>>         int rc;
> >>>
> >>> -       if (priv->irq == 0)
> >>> -               return;
> >>> -
> >>>         rc = tpm_tis_read32(priv, TPM_INT_ENABLE(priv->locality), &intmask);
> >>>         if (rc < 0)
> >>>                 intmask = 0;
> >>>
> >>>         intmask &= ~TPM_GLOBAL_INT_ENABLE;
> >>>         rc = tpm_tis_write32(priv, TPM_INT_ENABLE(priv->locality), intmask);
> >>> +       chip->flags &= ~TPM_CHIP_FLAG_IRQ;
> >>> +}
> >>> +
> >>> +static void disable_interrupts(struct tpm_chip *chip)
> >>> +{
> >>> +       struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> >>>
> >>> +       if (priv->irq == 0)
> >>> +               return;
> >>> +
> >>> +       __disable_interrupts(chip);
> >>>         devm_free_irq(chip->dev.parent, priv->irq, chip);
> >>>         priv->irq = 0;
> >>> -       chip->flags &= ~TPM_CHIP_FLAG_IRQ;
> >>>  }
> >>>
> >>>  /*
> >>> @@ -528,6 +539,12 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
> >>>         int rc, irq;
> >>>         struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> >>>
> >>> +       if (unlikely(storm_killed)) {
> >>> +               devm_free_irq(chip->dev.parent, priv->irq, chip);
> >>> +               priv->irq = 0;
> >>> +               storm_killed = false;
> >>> +       }
> >>
> >> OK this kind of bad solution because if tpm_tis_send() is not called,
> >> then IRQ is never freed. AFAIK, devres_* do not sleep but use spin
> >> lock, i.e. you could render out both storm_check and storm_killed.
> >>
> > 
> > Is there a way to flag it for freeing later while in an interrupt
> > context? I'm not sure where to clean it up since devm_free_irq can't be
> > called in tis_int_handler.
> 
> You could add a workqueue work-struct just for this and queue that up
> to do the free when you detect the storm. That will then run pretty much
> immediately, avoiding the storm going on for (much) longer.

That's sounds feasible.

> > Before diving further into that though, does anyone else have an opinion
> > on ripping out the irq code, and just using polling? We've been only
> > polling since 2015 anyways.
> 
> Given James Bottomley's reply I guess it would be worthwhile to get the
> storm detection to work.

OK, agreed. I take my words back from a response few minutes ago :-)

> Regards,
> 
> Hans

/Jarkko