linux-kernel - Re: init_tis() takes 50 ms on Dell XPS 13 9360 – almost 10 % of whole time until initrd

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Date: Fri, 16 Feb 2024 23:20:11 +0100
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Jarkko Sakkinen <jarkko@...nel.org>, 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

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?


Kind regards,

Paul