From: Tim Chen <tim.c.chen@linux.intel.com>
To: speck@linutronix.de
Subject: [MODERATED] Encrypted Message
Date: Fri, 18 May 2018 12:50:58 -0700 [thread overview]
Message-ID: <1eb46f22-9115-7977-7631-9d8fcfc98447@linux.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1805181615410.2172@nanos.tec.linutronix.de>
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From: Tim Chen <tim.c.chen@linux.intel.com>
To: speck for Thomas Gleixner <speck@linutronix.de>
Subject: Re: Is: Sleep states ?Was:Re: SSB status - V18 pushed out
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On 05/18/2018 07:29 AM, speck for Thomas Gleixner wrote:
> On Fri, 18 May 2018, speck for Konrad Rzeszutek Wilk wrote:
>> On Thu, May 17, 2018 at 10:53:28PM +0200, speck for Thomas Gleixner wrote:
>>> Folks,
>>>
>>> we finally reached a stable state with the SSB patches. I've updated all 3
>>> branches master/linux-4.16.y/linux-4.14.y in the repo and attached the
>>> resulting git bundles. They merge cleanly on top of the current HEADs of
>>> the relevant trees.
>>>
>>> The lot survived light testing on my side and it would be great if everyone
>>> involved could expose it to their test scenarios.
>>>
>>> Thanks to everyone who participated in that effort (patches, review,
>>> testing ...)!
>>
>> Yeey! Thank you.
>>
>> I was reading the updated Intel doc today (instead of skim reading it) and it mentioned:
>>
>> "Intel recommends that the SSBD MSR bit be cleared when in a sleep state on such processors."
>
> Well, the same recommendation was for IBRS and the reason is that with HT
> enabled the other hyperthread will not be able to go full speed because the
> sleeping one vanished with IBRS set. SSBD works the same way.
>
> " SW should clear [SSBD] when enter sleep state, just as is suggested for
> IBRS and STIBP on existing implementations"
>
> and that document says:
>
> "Enabling IBRS on one logical processor of a core with Intel
> Hyper-Threading Technology may affect branch prediction on other logical
> processors of the same core. For this reason, software should disable IBRS
> (by clearing IA32_SPEC_CTRL.IBRS) prior to entering a sleep state (e.g.,
> by executing HLT or MWAIT) and re-enable IBRS upon wakeup and prior to
> executing any indirect branch."
>
> So it's only a performance issue and not a fundamental problem to have it
> on when executing HLT/MWAIT
>
> So we have two situations here:
>
> 1) ssbd = on, i.e X86_FEATURE_SPEC_STORE_BYPASS_DISABLE
>
> There it is irrelevant because both threads have SSBD set permanentely,
> so unsetting it on HLT/MWAIT is not going to lift the restriction for
> the running sibling thread. And HLT/MWAIT is not going to be faster by
> unsetting it and then setting it on wakeup again....
>
> 2) SSBD via prctl/seccomp
>
> Nothing to do there, because idle task does not have TIF_SSBD set so it
> never goes with SSBD set into HLT/MWAIT.
>
> So I think we're good, but it would be nice if Intel folks would confirm
> that.
Yes, we have thought about turning off SSBD in the mwait path earlier. But
decided that it was unnecessary for the exact reasons Thomas mentioned.
Thanks.
Tim
next prev parent reply other threads:[~2018-05-18 19:51 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-17 20:53 SSB status - V18 pushed out Thomas Gleixner
2018-05-18 13:54 ` [MODERATED] Is: Sleep states ?Was:Re: " Konrad Rzeszutek Wilk
2018-05-18 14:29 ` Thomas Gleixner
2018-05-18 19:50 ` Tim Chen [this message]
-- strict thread matches above, loose matches on Subject: below --
2019-03-05 16:43 [MODERATED] Starting to go public? Linus Torvalds
2019-03-05 17:02 ` [MODERATED] " Andrew Cooper
2019-03-05 20:36 ` Jiri Kosina
2019-03-05 22:31 ` Andrew Cooper
2019-03-06 16:18 ` [MODERATED] Encrypted Message Jon Masters
2019-03-05 17:10 ` Jon Masters
2019-03-04 1:21 [MODERATED] [PATCH RFC 0/4] Proposed cmdline improvements Josh Poimboeuf
2019-03-04 1:23 ` [MODERATED] [PATCH RFC 1/4] 1 Josh Poimboeuf
2019-03-04 3:55 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 7:30 ` [MODERATED] Re: [PATCH RFC 1/4] 1 Greg KH
2019-03-04 7:45 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 1:24 ` [MODERATED] [PATCH RFC 3/4] 3 Josh Poimboeuf
2019-03-04 3:58 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 17:17 ` [MODERATED] " Josh Poimboeuf
2019-03-06 16:22 ` [MODERATED] " Jon Masters
2019-03-04 1:25 ` [MODERATED] [PATCH RFC 4/4] 4 Josh Poimboeuf
2019-03-04 4:07 ` [MODERATED] Encrypted Message Jon Masters
2019-03-01 21:47 [patch V6 00/14] MDS basics 0 Thomas Gleixner
2019-03-01 21:47 ` [patch V6 06/14] MDS basics 6 Thomas Gleixner
2019-03-04 6:28 ` [MODERATED] Encrypted Message Jon Masters
2019-03-01 21:47 ` [patch V6 08/14] MDS basics 8 Thomas Gleixner
2019-03-04 6:57 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 7:06 ` Jon Masters
2019-03-04 8:12 ` Jon Masters
2019-03-05 15:34 ` Thomas Gleixner
2019-03-06 16:21 ` [MODERATED] " Jon Masters
2019-03-01 21:47 ` [patch V6 10/14] MDS basics 10 Thomas Gleixner
2019-03-04 6:45 ` [MODERATED] Encrypted Message Jon Masters
2019-03-01 21:47 ` [patch V6 12/14] MDS basics 12 Thomas Gleixner
2019-03-04 5:47 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 5:30 ` Jon Masters
2019-02-24 15:07 [MODERATED] [PATCH v6 00/43] MDSv6 Andi Kleen
2019-02-24 15:07 ` [MODERATED] [PATCH v6 10/43] MDSv6 Andi Kleen
2019-02-25 16:30 ` [MODERATED] " Greg KH
2019-02-25 16:41 ` [MODERATED] Encrypted Message Jon Masters
2019-02-24 15:07 ` [MODERATED] [PATCH v6 31/43] MDSv6 Andi Kleen
2019-02-25 15:19 ` [MODERATED] " Greg KH
2019-02-25 15:34 ` Andi Kleen
2019-02-25 15:49 ` Greg KH
2019-02-25 15:52 ` [MODERATED] Encrypted Message Jon Masters
2019-02-25 16:00 ` [MODERATED] " Greg KH
2019-02-25 16:19 ` [MODERATED] " Jon Masters
2019-02-22 22:24 [patch V4 00/11] MDS basics Thomas Gleixner
2019-02-22 22:24 ` [patch V4 04/11] x86/speculation/mds: Add mds_clear_cpu_buffer() Thomas Gleixner
2019-02-26 14:19 ` [MODERATED] " Josh Poimboeuf
2019-03-01 20:58 ` [MODERATED] Encrypted Message Jon Masters
2019-03-01 22:14 ` Jon Masters
2019-02-21 23:44 [patch V3 0/9] MDS basics 0 Thomas Gleixner
2019-02-21 23:44 ` [patch V3 4/9] MDS basics 4 Thomas Gleixner
2019-02-22 7:45 ` [MODERATED] Encrypted Message Jon Masters
2019-02-20 15:07 [patch V2 00/10] MDS basics+ 0 Thomas Gleixner
2019-02-20 15:07 ` [patch V2 04/10] MDS basics+ 4 Thomas Gleixner
2019-02-20 17:10 ` [MODERATED] " mark gross
2019-02-21 19:26 ` [MODERATED] Encrypted Message Tim Chen
2019-02-19 12:44 [patch 0/8] MDS basics 0 Thomas Gleixner
2019-02-21 16:14 ` [MODERATED] Encrypted Message Jon Masters
2019-02-07 23:41 [MODERATED] [PATCH v3 0/6] PERFv3 Andi Kleen
2019-02-07 23:41 ` [MODERATED] [PATCH v3 2/6] PERFv3 Andi Kleen
2019-02-08 0:51 ` [MODERATED] Re: [SUSPECTED SPAM][PATCH " Andrew Cooper
2019-02-08 9:01 ` Peter Zijlstra
2019-02-08 9:39 ` Peter Zijlstra
2019-02-08 10:53 ` [MODERATED] [RFC][PATCH] performance walnuts Peter Zijlstra
2019-02-15 23:45 ` [MODERATED] Encrypted Message Jon Masters
2019-01-12 1:29 [MODERATED] [PATCH v4 00/28] MDSv4 2 Andi Kleen
2019-01-12 1:29 ` [MODERATED] [PATCH v4 05/28] MDSv4 10 Andi Kleen
2019-01-14 19:20 ` [MODERATED] " Dave Hansen
2019-01-18 7:33 ` [MODERATED] Encrypted Message Jon Masters
2019-01-14 23:39 ` Tim Chen
2019-01-12 1:29 ` [MODERATED] [PATCH v4 10/28] MDSv4 24 Andi Kleen
2019-01-15 1:05 ` [MODERATED] Encrypted Message Tim Chen
2018-06-12 17:29 [MODERATED] FYI - Reading uncached memory Jon Masters
2018-06-14 16:59 ` [MODERATED] Encrypted Message Tim Chen
2018-05-29 19:42 [MODERATED] [PATCH 0/2] L1TF KVM 0 Paolo Bonzini
[not found] ` <20180529194240.7F1336110A@crypto-ml.lab.linutronix.de>
2018-05-29 22:49 ` [PATCH 1/2] L1TF KVM 1 Thomas Gleixner
2018-05-29 23:54 ` [MODERATED] " Andrew Cooper
2018-05-30 9:01 ` Paolo Bonzini
2018-06-04 8:24 ` [MODERATED] " Martin Pohlack
2018-06-04 13:11 ` [MODERATED] Is: Tim, Q to you. Was:Re: " Konrad Rzeszutek Wilk
2018-06-04 17:59 ` [MODERATED] Encrypted Message Tim Chen
2018-06-05 23:34 ` Tim Chen
2018-06-05 23:37 ` Tim Chen
2018-06-07 19:11 ` Tim Chen
2018-05-02 21:51 [patch V11 00/16] SSB 0 Thomas Gleixner
2018-05-03 4:27 ` [MODERATED] Encrypted Message Tim Chen
2018-04-24 9:06 [MODERATED] L1D-Fault KVM mitigation Joerg Roedel
2018-04-24 9:35 ` [MODERATED] " Peter Zijlstra
2018-04-24 9:48 ` David Woodhouse
2018-04-24 11:04 ` Peter Zijlstra
2018-05-23 9:45 ` David Woodhouse
2018-05-24 9:45 ` Peter Zijlstra
2018-05-24 15:04 ` Thomas Gleixner
2018-05-24 15:33 ` Thomas Gleixner
2018-05-24 23:18 ` [MODERATED] Encrypted Message Tim Chen
2018-05-25 18:22 ` Tim Chen
2018-05-26 19:14 ` L1D-Fault KVM mitigation Thomas Gleixner
2018-05-29 19:29 ` [MODERATED] Encrypted Message Tim Chen
2018-05-29 21:14 ` L1D-Fault KVM mitigation Thomas Gleixner
2018-05-30 16:38 ` [MODERATED] Encrypted Message Tim Chen
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