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

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Date:	Wed, 30 Jul 2008 11:28:17 +0200
From:	Peter Oruba <peter.oruba@....com>
To:	Max Krasnyansky <maxk@...lcomm.com>
CC:	Dmitry Adamushko <dmitry.adamushko@...il.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


Max Krasnyansky schrieb:
> Dmitry Adamushko wrote:
>> 2008/7/29 Peter Oruba <peter.oruba@....com>:
>>> Fixed coding style issues.
>>
>> I have a comment on the abstraction layer (microcode_ops).
>>
>> [ Not that I've looked very carefully at it so far, nor I pretend to
>> be at-ease with this 'microcode' topic to make any design judgements
>> :-) ]
>>
>> but would it be somehow possible to not have set_cpus_allowed_ptr()
>> code in arch-dependent parts? Let's say the mechanism of how to run
>> certain arch-specific code (and synchronization) on a given cpu should
>> be a prerogative of (and placed in) the generic part...
>>
>> Note, this code will likely happily give you an oops if you run
>> cpu_down/up() ;-)
>>
>> I also wondered, is there a requirement that when a new cpu is brought
>> up, microcode updates {should,must} be done as early as possible, say
>> before any tasks have a chance to run on it? Or can the update be a
>> bit delayed? e.g. we don't do it from cpu-hotplug handlers.
> 
> Dmitry looks like you missed my email. I already asked that question and 
> proposed a couple of options (workqueue and ipi).
> Tigran said that he does not know. Maybe Peter does.
> 
> My guess is that it does not have to be done synchronously and can be 
> delayed. There is no guaranty that microcode CPU hotplug handler will 
> run before all the other handlers. Which by definition means that some 
> things will start running on the cpu before the microcode is updated. 
> Hence we might as well do the update outside of the cpu hotplug path.
> 
> Max
> 
> 
> 
> 

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.

Peter

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