linux-kernel - Re: [BUGFIX][PATCH] Freezer, CPU hotplug, x86 Microcode: Fix task freezing failures

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Date:	Mon, 3 Oct 2011 10:47:54 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Tejun Heo <tj@...nel.org>, "Rafael J. Wysocki" <rjw@...k.pl>,
	tigran@...azian.fsnet.co.uk, tglx@...utronix.de, mingo@...e.hu,
	hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [BUGFIX][PATCH] Freezer, CPU hotplug, x86 Microcode: Fix task
 freezing failures

Hi Srivatsa,

On Mon, Oct 03, 2011 at 11:21:49AM +0530, Srivatsa S. Bhat wrote:
> So my one-liner patch here tries to solve this problem by not
> invalidating the microcode at all, to handle the corner case of a CPU
> hotplug going on in parallel with freezer operations. But it creates
> issues with the usecase you described.

I think your patch makes sense because re-loading the ucode during
a suspend/resume cycle is unnecessary. If one wants to update the
microcode, it should happen later when the box is resumed again: you
simply put the new microcode image in /lib/firmware/... and on AMD
unload/reload the microcode module and on Intel you do either that or
use the deprecated microcode_ctl.

However, let me test it on a couple of AMD boxes tomorrow to verify.

> At the moment I can't think of any clean solution that solves both these problems - 
>   a. The problem of requesting microcode from userspace when it is frozen (which can be individually
>      solved by my patch).
>   b. The possible need for a revised microcode during CPU online (due to the remote usecase of 
>      physically plugging-out and plugging-in a new CPU), when the tasks are frozen.

Yeah, let me remind you guys, we're talking about x86 CPUs here. AFAICT,
I don't think that physical unplug is supported by any vendor yet but
I'd welcome surprises :-).

Thanks.

-- 
Regards/Gruss,
    Boris.
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