linux-kernel - Re: question about setting TPM_CHIP_FLAG_IRQ in tpm_tis_core

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Date:   Thu, 14 Nov 2019 18:48:41 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: question about setting TPM_CHIP_FLAG_IRQ in tpm_tis_core_init

On Tue, Nov 12, 2019 at 03:30:51PM -0500, Stefan Berger wrote:
> On 11/12/19 3:17 PM, Jerry Snitselaar wrote:
> > On Tue Nov 12 19, Jarkko Sakkinen wrote:
> > > On Mon, Nov 11, 2019 at 08:36:37PM -0700, Jerry Snitselaar wrote:
> > > > Question about 1ea32c83c699 ("tpm_tis_core: Set TPM_CHIP_FLAG_IRQ
> > > > before probing for interrupts").  Doesn't tpm_tis_send set this flag,
> > > > and setting it here in tpm_tis_core_init short circuits what
> > > > tpm_tis_send was doing before? There is a bug report of an interrupt
> > > > storm from a tpm on a t490s laptop with the Fedora 31 kernel (5.3),
> > > > and I'm wondering if this change could cause that. Before they got the
> > > > warning about interrupts not working, and using polling instead.
> > > 
> > > Looks like it. Stefan?
> > > 
> > > /Jarkko
> > > 
> > 
> > Stefan is right about the condition check at the beginning of
> > tpm_tis_send.
> > 
> >     if (!(chip->flags & TPM_CHIP_FLAG_IRQ) || priv->irq_tested)
> >         return tpm_tis_send_main(chip, buf, len);
> > 
> > Before his change it would've gone straight to calling
> > tpm_tis_send_main instead of jumping down and doing the irq test, due
> > to the flag not being set. With his change it should now skip this
> > tpm_tis_send_main call when tpm_tis_gen_interrupt is called, and then
> > after that time through tpm_tis_send priv->irq_tested will be set, and
> > the flag should be set as to whether or not irqs were working.
> > 
> > I should hopefully have access to a t490s in a few days so I can look at
> > it,
> > and try to figure out what is happening.
> > 
> I hope the t490s is an outlier. Give the patch I just posted a try.

First I must be first that it is the best way to fix the bug. Also,
it did not have fixes tag.

/Jarkko