From: "Jan Beulich" <JBeulich@suse.com>
To: Chao Gao <chao.gao@intel.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
Wei Liu <wei.liu2@citrix.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH v4 4/6] microcode: don't call apply_microcode() in cpu_request_microcode()
Date: Fri, 30 Nov 2018 02:38:02 -0700 [thread overview]
Message-ID: <5C0104FA0200007800201813@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <20181130085745.GB32365@gao-cwp>
>>> On 30.11.18 at 09:57, <chao.gao@intel.com> wrote:
> On Thu, Nov 29, 2018 at 10:46:05AM +0100, Roger Pau Monné wrote:
>>On Thu, Nov 29, 2018 at 12:28:46PM +0800, Chao Gao wrote:
>>> It is better that all CPUs have the same microcode revision.
>>>
>>> Linux kernel rejects late microcode update if finding some CPUs
>>> offlined. I may port this patch to Xen too in a separate patch.
>>
>>What happens with hotplug CPUs?
>>
>>Even if you disable late loading when there are offlined CPUs you
>>still need to handle hotplug CPUs, which IMO should share the same
>>path with offlined CPUs: the microcode update should be done ASAP
>>after bringing the CPU up.
>
> In linux, CPU's being offline is just a logical offline. It may participate
> actions like MCE. It would lead to a situation that some cpus are using old
> microcode while some are using the new one, which introduces instability.
> CPU hotplug doesn't have such issue.
But please be careful not to disallow ucode loading in cases where
doing so is fine. I'm in particular thinking about "smt=no", where
secondary hyperthreads get parked. Since ucode updates on one
hyperthread of a core affect all hyperthreads, updating is fine in
this particular case.
Furthermore, if you look at my patch series "x86: more power-
efficient CPU parking", it is also within realm of possibility to
briefly wake up parked CPUs, just to get their ucode updated.
Jan
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next prev parent reply other threads:[~2018-11-30 9:38 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-28 5:34 [PATCH v4 0/6] improve late microcode loading Chao Gao
2018-11-28 5:34 ` [PATCH v4 1/6] microcode/intel: extend microcode_update_match() Chao Gao
2018-11-28 10:58 ` Roger Pau Monné
2018-11-29 2:00 ` Chao Gao
2018-11-29 9:14 ` Roger Pau Monné
2018-11-28 5:34 ` [PATCH v4 2/6] microcode: save all microcodes which pass sanity check Chao Gao
2018-11-28 12:00 ` Roger Pau Monné
2018-11-29 2:40 ` Chao Gao
2018-11-29 9:22 ` Roger Pau Monné
2018-11-30 7:55 ` Chao Gao
2018-11-30 9:32 ` Jan Beulich
2019-01-15 15:07 ` Andrew Cooper
2018-12-04 22:39 ` Woods, Brian
2018-12-05 7:38 ` Chao Gao
2018-11-29 10:19 ` Jan Beulich
2019-01-15 15:15 ` Andrew Cooper
2018-11-28 5:34 ` [PATCH v4 3/6] microcode: delete 'mc' field from struct ucode_cpu_info Chao Gao
2018-11-28 12:32 ` Roger Pau Monné
2018-11-28 5:34 ` [PATCH v4 4/6] microcode: don't call apply_microcode() in cpu_request_microcode() Chao Gao
2018-11-28 15:02 ` Roger Pau Monné
2018-11-29 4:28 ` Chao Gao
2018-11-29 9:46 ` Roger Pau Monné
2018-11-30 8:57 ` Chao Gao
2018-11-30 9:38 ` Jan Beulich [this message]
2018-11-28 5:34 ` [PATCH v4 5/6] microcode: delete microcode pointer and size from microcode_info Chao Gao
2018-11-28 15:04 ` Roger Pau Monné
2018-11-28 5:34 ` [PATCH v4 6/6] x86/microcode: Synchronize late microcode loading Chao Gao
2018-11-28 15:22 ` Roger Pau Monné
2018-11-29 4:43 ` Chao Gao
2018-11-29 9:56 ` Roger Pau Monné
2018-11-29 22:43 ` Boris Ostrovsky
2018-11-30 9:46 ` Jan Beulich
2018-11-30 16:49 ` Boris Ostrovsky
2018-11-30 9:01 ` Chao Gao
2019-01-15 15:24 ` Andrew Cooper
2019-01-15 16:24 ` Roger Pau Monné
2018-12-11 17:01 ` Jan Beulich
2018-12-11 18:16 ` Raj, Ashok
2018-12-12 7:26 ` Jan Beulich
2018-12-13 2:10 ` Boris Ostrovsky
2018-12-12 4:53 ` Chao Gao
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