linux-kernel - Re: [PATCH v3 0/2] tpm: add support for nonblocking operation

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Date:   Tue, 19 Jun 2018 16:10:46 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Tadeusz Struk <tadeusz.struk@...el.com>
Cc:     jgg@...pe.ca, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, philip.b.tricca@...el.com,
        James.Bottomley@...senPartnership.com
Subject: Re: [PATCH v3 0/2] tpm: add support for nonblocking operation

On Tue, Jun 12, 2018 at 10:58:26AM -0700, Tadeusz Struk wrote:
> The TCG SAPI specification [1] defines a set of functions, which allows
> applications to use the TPM device in either blocking or non-blocking fashion.
> Each command defined by the specification has a corresponding
> Tss2_Sys_<COMMAND>_Prepare() and Tss2_Sys_<COMMAND>_Complete() call, which
> together with Tss2_Sys_ExecuteAsync() is designed to allow asynchronous
> mode of operation. Currently the TPM driver supports only blocking calls,
> which doesn't allow asynchronous IO operations.
> This patch changes it and adds support for nonblocking write and a new poll
> function to enable applications, which want to take advantage of this feature.
> The new functionality can be tested using standard TPM tools implemented
> in [2], together with modified TCTI from [3].
> 
> [1] https://trustedcomputinggroup.org/wp-content/uploads/TSS_SAPI_Version-1.1_Revision-22_review_030918.pdf
> [2] https://github.com/tpm2-software/tpm2-tools
> [3] https://github.com/tstruk/tpm2-tss/tree/async

For me the value is still a bit questionable. The benchmark looks a bit
flakky to give much figures how this would work with real world workloads.

I read James response and I also have to question why not just a worker
thread in user space? TPM does only one command at a time anyways.

Cannot take this in before I know that user space will (1) adapt to
this and (2) gain value compared to a worker thread.

/Jarkko