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From:   Jerry Snitselaar <jsnitsel@redhat.com>
To:     Jarkko Sakkinen <jarkko@kernel.org>
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
In-reply-to: <20201124032623.GA40007@kernel.org>
Date:   Tue, 24 Nov 2020 10:52:56 -0700
Message-ID: <871rgiod53.fsf@redhat.com>
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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.

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.

>> +
>>         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