> On Oct 1, 2020, at 4:04 PM, Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote: > > On Thu, Oct 01, 2020 at 11:32:59AM -0700, James Bottomley wrote: >> On Thu, 2020-10-01 at 14:15 -0400, Nayna wrote: >>> On 10/1/20 12:53 AM, James Bottomley wrote: >>>> On Thu, 2020-10-01 at 04:50 +0300, Jarkko Sakkinen wrote: >>>>> On Wed, Sep 30, 2020 at 03:31:20PM -0700, James Bottomley wrote: >>>>>> On Thu, 2020-10-01 at 00:09 +0300, Jarkko Sakkinen wrote: >> [...] >>>>>>> I also wonder if we could adjust the frequency dynamically. >>>>>>> I.e. start with optimistic value and lower it until finding >>>>>>> the sweet spot. >>>>>> >>>>>> The problem is the way this crashes: the TPM seems to be >>>>>> unrecoverable. If it were recoverable without a hard reset of >>>>>> the entire machine, we could certainly play around with it. I >>>>>> can try alternative mechanisms to see if anything's viable, but >>>>>> to all intents and purposes, it looks like my TPM simply stops >>>>>> responding to the TIS interface. >>>>> >>>>> A quickly scraped idea probably with some holes in it but I was >>>>> thinking something like >>>>> >>>>> 1. Initially set slow value for latency, this could be the >>>>> original 15 ms. >>>>> 2. Use this to read TPM_PT_VENDOR_STRING_*. >>>>> 3. Lookup based vendor string from a fixup table a latency that >>>>> works >>>>> (the fallback latency could be the existing latency). >>>> >>>> Well, yes, that was sort of what I was thinking of doing for the >>>> Atmel ... except I was thinking of using the TIS VID (16 byte >>>> assigned vendor ID) which means we can get the information to set >>>> the timeout before we have to do any TPM operations. >>> >>> I wonder if the timeout issue exists for all TPM commands for the >>> same manufacturer. For example, does the ATMEL TPM also crash when >>> extending PCRs ? >>> >>> In addition to defining a per TPM vendor based lookup table for >>> timeout, would it be a good idea to also define a Kconfig/boot param >>> option to allow timeout setting. This will enable to set the timeout >>> based on the specific use. >> >> I don't think we need go that far (yet). The timing change has been in >> upstream since: >> >> commit 424eaf910c329ab06ad03a527ef45dcf6a328f00 >> Author: Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx> >> Date: Wed May 16 01:51:25 2018 -0400 >> >> tpm: reduce polling time to usecs for even finer granularity >> >> Which was in the released kernel 4.18: over two years ago. In all that >> time we've discovered two problems: mine which looks to be an artifact >> of an experimental upgrade process in a new nuvoton and the Atmel. >> That means pretty much every other TPM simply works with the existing >> timings >> >>> I was also thinking how will we decide the lookup table values for >>> each vendor ? >> >> I wasn't thinking we would. I was thinking I'd do a simple exception >> for the Atmel and nothing else. I don't think my Nuvoton is in any way >> characteristic. Indeed my pluggable TPM rainbow bridge system works >> just fine with a Nuvoton and the current timings. >> >> We can add additional exceptions if they actually turn up. > > I'd add a table and fallback. > Hi folks, I want to follow up this a bit and check whether we reached a consensus on how to fix the timeout issue for Atmel chip. Should we revert the changes or introduce the lookup table for chips. Is there anything I can help from Rubrik side. Thanks Hao
