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

From: Jarkko Sakkinen <jarkko@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
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>,
	Matthew Garrett <mjg59@google.com>,
	linux-integrity@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Huewe <peterhuewe@gmx.de>
Subject: Re: [PATCH v3 3/4] tpm_tis: Disable interrupts if interrupt storm detected
Date: Tue, 8 Dec 2020 19:42:46 +0200	[thread overview]
Message-ID: <20201208174246.GB58213@kernel.org> (raw)
In-Reply-To: <20201207192803.GH5487@ziepe.ca>

On Mon, Dec 07, 2020 at 03:28:03PM -0400, Jason Gunthorpe wrote:
> 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

+1 for removing it.

/Jarkko
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