Re: [PATCH v3 3/4] tpm_tis: Disable interrupts if interrupt storm detected

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: intel-gfx@lists.freedesktop.org,
	Jerry Snitselaar <jsnitsel@redhat.com>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	James Bottomley <James.Bottomley@HansenPartnership.com>,
	Hans de Goede <hdegoede@redhat.com>,
	Jarkko Sakkinen <jarkko@kernel.org>,
	Matthew Garrett <mjg59@google.com>,
	linux-integrity@vger.kernel.org, Peter Huewe <peterhuewe@gmx.de>
Subject: Re: [PATCH v3 3/4] tpm_tis: Disable interrupts if interrupt storm detected
Date: Mon, 7 Dec 2020 15:28:03 -0400	[thread overview]
Message-ID: <20201207192803.GH5487@ziepe.ca> (raw)
In-Reply-To: <87tusy7n3b.fsf@nanos.tec.linutronix.de>

On Sun, Dec 06, 2020 at 08:26:16PM +0100, Thomas Gleixner wrote:
> Just as a side note. I was looking at tpm_tis_probe_irq_single() and
> that function is leaking the interrupt request if any of the checks
> afterwards fails, except for the final interrupt probe check which does
> a cleanup. That means on fail before that the interrupt handler stays
> requested up to the point where the module is removed. If that's a
> shared interrupt and some other device is active on the same line, then
> each interrupt from that device will call into the TPM code. Something
> like the below is needed.
> 
> Also the X86 autoprobe mechanism is interesting:
> 
> 	if (IS_ENABLED(CONFIG_X86))
> 		for (i = 3; i <= 15; i++)
> 			if (!tpm_tis_probe_irq_single(chip, intmask, 0, i))
> 				return;
> 
> The third argument is 'flags' which is handed to request_irq(). So that
> won't ever be able to probe a shared interrupt. But if an interrupt
> number > 0 is handed to tpm_tis_core_init() the interrupt is requested
> with IRQF_SHARED. Same issue when the chip has an interrupt number in
> the register. It's also requested exclusive which is pretty likely
> to fail on ancient x86 machines.

It is very likely none of this works any more, it has been repeatedly
reworked over the years and just left behind out of fear someone needs
it. I've thought it should be deleted for a while now.

I suppose the original logic was to try and probe without SHARED
because a probe would need exclusive access to the interrupt to tell
if the TPM was actually the source, not some other device.

It is all very old and very out of step with current thinking, IMHO. I
skeptical that TPM interrupts were ever valuable enough to deserve
this in the first place.

Jason
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