Re: [BUGFIX][PATCH] Freezer, CPU hotplug, x86 Microcode: Fix taskfreezing failures

From: Borislav Petkov
Date: Tue Oct 04 2011 - 13:14:20 EST

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.



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