linux-kernel - Re: [patch 0/4] x86: AMD microcode patch loading v2 fixes

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Date:	Wed, 30 Jul 2008 09:54:29 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
CC:	Peter Oruba <peter.oruba@....com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tigran Aivazian <tigran@...azian.fsnet.co.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch 0/4] x86: AMD microcode patch loading v2 fixes



Dmitry Adamushko wrote:
> 2008/7/30 Peter Oruba <peter.oruba@....com>:
>>> [ ... ]
>> Since ucode updates may fix severe issues, it is supposed to happen as early
>> as possible. If you re-plug your CPU into your socket, your BIOS also
>> applies a ucode patch, but that won't necessarily be the latest and critical
>> one.
Sure. The question is would not workqueue be soon enough ?
I'd say it is given the non-deterministic CPU hotplug callback sequence.

> Hum, let's say we don't do it from cpu-hotplug handlers [1] but from
> start_secondary() before calling cpu_idle()? [*]
> 
> This way, we do it before any other task may have a chance to run on a
> cpu which is not a case with cpu-hotplug handlers
> (and we don't mess-up with cpu-hotplug events :-)
> 
> [ the drawback is that 'microcode' subsystem is not local to
> microcode.c anymore ]
> 
> [1] if we need a sync. operation in cpu-hotplug handlers and IPI is
> not ok (say, we need to run in a sleepablel context) then perhaps it's
> workqueues + wait_on_cpu_work(). But then it's not a bit later than
> could have been with [*].
Why would not IPI be ok ? From looking at the code all we have to do is to
factor request_firmware() out of the update path. So we'd do
collect_cpu_info() in the IPI, then do request_firwmare() inplace and then do
apply_microcode() in the IPI. ie The only thing that sleeps is request_firmware().

Max
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