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From: Peter Huewe <peterhuewe-Mmb7MZpHnFY@public.gmane.org>
To: tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	Ken Goldman
	<kgold-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
Cc: linux-ima-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	linux-security-module-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH v2 1/4] tpm: ignore burstcount to improve tpm_tis send() performance.
Date: Wed, 13 Sep 2017 12:01:20 -0700	[thread overview]
Message-ID: <5C86BF5C-76AA-47DB-B15B-DE524823CF9F@gmx.de> (raw)
In-Reply-To: <3c418974-a4c7-518e-b218-f6373c10209e-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>



Am 13. September 2017 11:52:12 GMT-07:00 schrieb Ken Goldman <kgold-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>:
>On 9/6/2017 12:12 PM, Jason Gunthorpe wrote:
>> 
>> The problem with this approach is that the TPM could totally block
>> the CPU for very long periods of time.
>> 
>> It seems very risky to enable..
>> 
>
>How would you characterize "very long"?
>
>The TPM vendors confirm that they empty the FIFO at internal speeds
>that
>are comparable to the bus speed.  Thus, any stall will be sub-usec.  Is
>that an issue?

If the tpm does behave correctly, this is fine. 
If the tpm hangs for whatever reason, your machine is frozen and you will never figure out why.

That's my concern there.
However ddwg seems fine.

>
>In addition, new TPMs have ever larger FIFO's, making stalls less
>likely
>going forward.
But also reduced the polling loops that introduce the performance penalty ;)

>
>
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  parent reply	other threads:[~2017-09-13 19:01 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-06 12:56 [PATCH v2 0/4] additional TPM performance improvements Nayna Jain
2017-09-06 12:56 ` [PATCH v2 3/4] tpm: reduce tpm_msleep() time in get_burstcount() Nayna Jain
2017-09-13  1:00   ` Jarkko Sakkinen
2017-09-15 12:40     ` Nayna Jain
     [not found] ` <20170906125643.5070-1-nayna-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-09-06 12:56   ` [PATCH v2 1/4] tpm: ignore burstcount to improve tpm_tis send() performance Nayna Jain
2017-09-06 16:12     ` Jason Gunthorpe
2017-09-13 18:52       ` [tpmdd-devel] " Ken Goldman
     [not found]         ` <3c418974-a4c7-518e-b218-f6373c10209e-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-09-13 19:01           ` Peter Huewe [this message]
2017-09-13  0:45     ` Jarkko Sakkinen
     [not found]       ` <20170912222010.ltm76m5vy2kupydi-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2017-09-13 18:39         ` Peter Huewe
2017-09-13 23:10           ` Jarkko Sakkinen
2017-09-15 12:29             ` Nayna Jain
2017-09-15 15:19               ` Jarkko Sakkinen
2017-09-06 12:56   ` [PATCH v2 2/4] tpm: define __wait_for_tpm_stat to specify variable polling sleep time Nayna Jain
2017-09-13  0:58     ` Jarkko Sakkinen
2017-09-15 12:37       ` Nayna Jain
2017-09-15 15:20         ` Jarkko Sakkinen
2017-09-06 12:56   ` [PATCH v2 4/4] tpm: use tpm_msleep() value as max delay Nayna Jain
2017-09-13  0:47     ` Jarkko Sakkinen
2017-09-14  9:25       ` Nayna Jain
2017-09-14 12:28         ` Jarkko Sakkinen
2017-09-06 12:56   ` [PATCH 2/4] tpm: define __wait_for_tpm_stat to specify variable polling sleep time Nayna Jain
2017-09-06 12:58     ` Nayna
2017-09-06 12:56 ` [PATCH 1/4] tpm: ignore burstcount to improve tpm_tis send() performance Nayna Jain
     [not found]   ` <20170906125643.5070-6-nayna-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-09-06 12:58     ` Nayna
2017-09-07 16:18 ` [PATCH v2 0/4] additional TPM performance improvements Jarkko Sakkinen
2017-09-11 15:20 ` [tpmdd-devel] " Alexander.Steffen

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