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Subject: Re: [PATCH] tpm_tis: Disable interrupts on ThinkPad T490s
To:     Matthew Garrett <mjg59@google.com>,
        Jerry Snitselaar <jsnitsel@redhat.com>
Cc:     linux-integrity <linux-integrity@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        jarkko@kernel.org, Peter Huewe <peterhuewe@gmx.de>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        James Bottomley <James.Bottomley@hansenpartnership.com>
References: <20201015214430.17937-1-jsnitsel@redhat.com>
 <CACdnJuuAyBYacCiOOZ8-L-0Xnfa3+pCVY_oejOJ8RPzuG2QgrQ@mail.gmail.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <78839bb8-dd17-0e55-3d22-be476b71ece5@redhat.com>
Date:   Fri, 16 Oct 2020 08:12:23 +0200
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Hi,

On 10/16/20 12:39 AM, Matthew Garrett wrote:
> 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.

IIRC then at least on the T490 the irq storm caused systems to not boot
in some cases. I guess if we detect the storm and disable the irq we might
fix that... OTOH this problem seems to only hit a certain generation of
Thinkpads so with some luck the denylist should not be too big and the denylist
approach should work.

Regards,

Hans