Message-Id: <CZ9BWAZ1GRZG.96ETQPKT8ER4@seitikki>
Date: Mon, 19 Feb 2024 20:13:14 +0000
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Paul Menzel" <pmenzel@...gen.mpg.de>, "Peter Huewe" <peterhuewe@....de>
Cc: <linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: init_tis() takes 50 ms on Dell XPS 13 9360 – almost 10 % of whole time until initrd

On Fri Feb 16, 2024 at 10:20 PM UTC, Paul Menzel wrote:
> Dear Jarkko,
>
>
> Thank you for your reply.
>
> Am 16.02.24 um 23:07 schrieb Jarkko Sakkinen:
> > On Wed Feb 14, 2024 at 3:10 PM UTC, Paul Menzel wrote:
>
> >> Trying to optimize the boot time of Linux on the Dell XPS 13 9360,
> >> probing of MSFT0101:00 takes 52 ms, making `init_tis()` taking almost 10
> >> % alone until starting the initrd:
> >>
> >>       [    0.000000] Linux version 6.8.0-rc4 (build@...emianrhapsody.molgen.mpg.de) (gcc (Debian 13.2.0-13) 13.2.0,
> >> GNU ld (GNU Binutils for Debian) 2.42) #20 SMP PREEMPT_DYNAMIC Mon Feb 12 09:40:49 CET 2024
> >>       […]
> >>       [    0.000000] DMI: Dell Inc. XPS 13 9360/0596KF, BIOS 2.21.0 06/02/2022
> >>       […]
> >>       [    0.320057] calling  init_tis+0x0/0x100 @ 1
> >>       [    0.332190] tpm_tis MSFT0101:00: 2.0 TPM (device-id 0xFE, rev-id 4)
> >>       [    0.372164] probe of MSFT0101:00 returned 0 after 52101 usecs
> >>       [    0.372186] initcall init_tis+0x0/0x100 returned 0 after 52127 usecs
> >>       […]
> >>       [    0.588643] Freeing unused decrypted memory: 2036K
> >>       [    0.589068] Freeing unused kernel image (initmem) memory: 3976K
> >>       [    0.606115] Write protecting the kernel read-only data: 22528k
> >>       [    0.606527] Freeing unused kernel image (rodata/data gap) memory: 276K
> >>       [    0.652327] x86/mm: Checked W+X mappings: passed, no W+X pages found.
> >>       [    0.652329] x86/mm: Checking user space page tables
> >>       [    0.695968] x86/mm: Checked W+X mappings: passed, no W+X pages found.
> >>       [    0.696104] Run /init as init process
> >>       […]
> >>
> >> For users, where boot time is most important, can this be moved out of
> >> the hot path somehow?
> > 
> > It can't be IRQ probing as IRQ's are *disabled* by default. So we can
> > disclose that.
> > 
> > I think the delay is caused by tpm2_probe(), which is called by
> > tpm_tis_core_init(). It sends an idempotent TPM2 command to the TPM
> > chip to know whether it is TPM 1.x or TPM2 chip.
> > 
> > That detection is definitely required.
> > 
> > Even some other subsystems in the kernel require to know the correct
> > TPM version, like hwrng and IMA.
> Understood. The TPM in my laptop does not change, so could this be 
> cached, or does a Linux CLI paramater exist, that I can specify the version?

Oops, I totally ignored tpm_chip_register() which runs more TPM commands:

1. PCR alloction: tpm2_get_pcr_allocation()
2. self-test: tpm2_do_selftest()

(in some cases also tpm2_startup())

Just probe (a single trivial TPM command doing zero calcuation) causing
that long delay would not make sense, so sorry for misleading with this!

So the problem here is in-kernel clients of TPM that initialize during
the boot such as IMA and hwrng.

The call for tpm_chip_register() is in the tail of each chip driver,
i.e. it is in the "overall" framework and thus theoretically could be
relocated to a workqueue. This requires tho changes to all clients and
error code for the case where tpm_transmit() flushes this workqueue but
initialization fails.

So *I think* (was not fully scientifical feasibility study) it is
possible but it is not as small change as you would first think. 

> Kind regards,
>
> Paul

BR, Jarkko

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