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SubjectRe: [PATCH v4 0/7] x86: BSP or CPU0 online/offline
On 12/06/2011 06:30 PM, Borislav Petkov wrote:

> On Tue, Dec 06, 2011 at 04:17:58PM +0530, Srivatsa S. Bhat wrote:
>> In this case, the other patch that I mentioned in my previous mail
>> would be required (or an equivalent), because the optimization
>> patch which is now in mainline, would apply the same old microcode
>> image on this new CPU too, blindly.
> Not blindly, the microcode is still verified.

I saw your other mail about the validity of this whole scenario, and I
kind of agree to your point.

My thoughts below might not be so relevant/significant considering that,
but anyways, just to understand what you said above:
I didn't quite find where the microcode is verified if the kernel happens
to have the microcode image already.

From what I saw, microcode image is not freed nor invalidated when a
CPU goes down (which was introduced by the optimization patch). And hence,
when the CPU comes back up, the call sequence would look something like:

* microcode_update_cpu(cpu);
* microcode_resume_cpu(cpu) /* Because uci->valid was 1 */
* eventually calls apply_microcode_amd(cpu) for AMD or
apply_microcode(cpu) for Intel

And both these functions simply write the microcode image to the CPU
and then check whether the _write_ was successful, (not whether the required
microcode version was applied).

That was why, to take care of this, the other patch (below) was written, IMHO.

Srivatsa S. Bhat

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