linux-kernel - Re: [PATCH v3 2/2] x86/microcode/core: Take a snapshot before and after applying microcode

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Date:   Wed, 28 Dec 2022 10:36:22 -0800
From:   Ashok Raj <ashok.raj@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     X86-kernel <x86@...nel.org>,
        LKML Mailing List <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        "Tony Luck" <tony.luck@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v3 2/2] x86/microcode/core: Take a snapshot before and
 after applying microcode

On Tue, Dec 27, 2022 at 01:01:44PM -0800, Ashok Raj wrote:
> The kernel caches features about each CPU's features at boot in an
> x86_capability[] structure. The microcode update takes one snapshot and
> compares it with the saved copy at boot.
> 
> However, the capabilities in the boot copy can be turned off as a result of
> certain command line parameters or configuration restrictions. This can
> cause a mismatch when comparing the values before and after the microcode
> update.
> 
> microcode_check() is called after an update to report any previously
> cached CPUID bits might have changed due to the update.
> 

I'll send you a clean version. Somehow this picked up an interim change and
the change to microcode_check() is not there. I remember testing but it
happened to be a different system I updated. 

I'll send something after the new years.. working during holidays isn't
efficient :-(.


Cheers,
Ashok