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

From: Borislav Petkov
Date: Tue Oct 04 2011 - 09:46:57 EST

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.


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