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

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Date:	Tue, 4 Oct 2011 21:49:30 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Borislav Petkov <bp@...64.org>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Borislav Petkov <bp@...en8.de>, Tejun Heo <tj@...nel.org>,
	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

On Tuesday, October 04, 2011, Borislav Petkov wrote:
> On Tue, Oct 04, 2011 at 03:46:53PM +0200, Borislav Petkov wrote:
> > On Tue, Oct 04, 2011 at 06:45:12PM +0530, Srivatsa S. Bhat wrote:
> > > I would like to propose a modified solution to the problem:
> > > 
> > > Taking a CPU offline:
> > > * Upon a CPU_DEAD notification, just like the code originally did, we free
> > >   the kernel's copy of the microcode and invalidate it. So no changes here.
> > >  
> > > Bringing a CPU online:
> > > * When a CPU_ONLINE or CPU_ONLINE_FROZEN notification is received, 
> > >   a. If the userspace is not frozen, we request microcode from userspace and
> > >      apply it to the cpu.
> > > 
> > >   b. However if we find that the userspace is frozen at that moment, we defer
> > >      applying microcode now and register a callback function to be executed
> > >      immediately when the userspace gets thawed. This callback function would
> > >      request microcode from userspace and apply it to the cpu.
> > 
> > No need for that if we can drop the whole re-requesting of ucode on
> > CPU_ONLINE* (see my other mail). Let me run some tests before though.
> 
> Ok, it looks good. I had one issue with what happens when there's no
> ucode image but the ucode driver is a bit-hmm... and that case actually
> magically works.
> 
> So you can have my Acked- and Tested-by:'s for the AMD side - you still
> need to test it on Intel with both microcode_ctl and the module un- and
> loading so that you make sure you're not introducing regressions, if you
> haven't done so yet, of course.

Cool, thanks.

I'd like to hear a voice from the Intel side too.

Thanks,
Rafael
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