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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx) (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
