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Date:   Tue, 24 Nov 2020 05:26:23 +0200
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Jerry Snitselaar <jsnitsel@redhat.com>
Cc:     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>,
        Hans de Goede <hdegoede@redhat.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [PATCH] tpm_tis: Disable interrupts on ThinkPad T490s
Message-ID: <20201124032623.GA40007@kernel.org>
References: <20201015214430.17937-1-jsnitsel@redhat.com>
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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.

> +
>  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.

> +
>         if (!(chip->flags & TPM_CHIP_FLAG_IRQ) || priv->irq_tested)
>                 return tpm_tis_send_main(chip, buf, len);
> 
> @@ -748,6 +765,21 @@ static irqreturn_t tis_int_handler(int dummy, void *dev_id)
>         u32 interrupt;
>         int i, rc;
> 
> +       if (storm_check) {
> +               irqs_fired++;
> +
> +               if (!time_start) {
> +                       time_start = jiffies_to_msecs(jiffies);
> +               } else if ((irqs_fired > 1000) && (jiffies_to_msecs(jiffies) - jiffies < 500)) {
> +                       __disable_interrupts(chip);
> +                       storm_check = false;
> +                       storm_killed = true;
> +                       return IRQ_HANDLED;
> +               } else if ((jiffies_to_msecs(jiffies) - time_start > 500) && (irqs_fired < 1000)) {
> +                       storm_check = false;
> +               }
> +       }
> +
>         rc = tpm_tis_read32(priv, TPM_INT_STATUS(priv->locality), &interrupt);
>         if (rc < 0)
>                 return IRQ_NONE;
> 
> 

/Jarkko