linux-kernel - Re: [PATCH] tpm/tpm_tis: Fix variable reset during IRQ probing

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Message-ID: <YAFfIqaohjneVCO6@kernel.org>
Date:   Fri, 15 Jan 2021 11:23:46 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia Zhang <zhang.jia@...ux.alibaba.com>
Subject: Re: [PATCH] tpm/tpm_tis: Fix variable reset during IRQ probing

On Thu, Jan 14, 2021 at 12:12:16PM +0800, Tianjia Zhang wrote:
> 
> 
> On 1/14/21 10:51 AM, Jarkko Sakkinen wrote:
> > On Wed, Jan 13, 2021 at 08:00:21PM +0800, Tianjia Zhang wrote:
> > > In tpm_tis_core_init(), tpm2_probe() will be called first, this
> > > function will eventually call tpm_tis_send(), and then
> > > tpm_tis_probe_irq_single() will detect whether the interrupt is
> > > normal, mainly the installation interrupted, set `priv->irq_tested`
> > > to false. The logic will eventually be executed to tpm_tis_send()
> > > to trigger an interrupt.
> > > 
> > > There is currently such a scenario, which will cause the IRQ probe
> > > code to never be executed, so that the TPM device is in polling
> > > mode: after setting irq_tested to false, an interrupt occurs
> > > between entering the ttpm_tis_send() function, and the interrupt
> > > will be first set irq_tested to true will cause the IRQ probe code
> > > to never be executed.
> > 
> > Can you describe the scenario more detail?
> > 
> 
> The problematic scenario we encountered is like this. The following figure
> shows the execution flow of tpm_tis_core_init(). An interrupt occurred
> before the IRQ probe. This interrupt was caused by tpm2_probe(), but it was
> triggered before the IRQ probe was executed, and the interrupt handler would
> set irq_tested to true, so the IRQ probe code can never execute, that is,
> the code marked 2 in the figure will never happen.

TPM_INT_ENABLE is cleared on reset [*].

[*] Section 5.9.1
    https://trustedcomputinggroup.org/resource/pc-client-work-group-pc-client-specific-tpm-interface-specification-tis/

/Jarkko