linux-kernel - Re: [PATCH v2] arch/x86: Fix boot_cpu

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Message-ID: <0a4c663887ecc1672d9927ed7256485b@natalenko.name>
Date:   Wed, 01 Aug 2018 16:16:42 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     bp@...en8.de, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org, sironi@...zon.de,
        stable@...r.kernel.org, tony.luck@...el.com
Subject: Re: [PATCH v2] arch/x86: Fix boot_cpu_data.microcode version output

Hi.

On 01.08.2018 13:38, Prarit Bhargava wrote:
>> After this patch, do we preserve an original microcode version 
>> somewhere? If no,
>> why? Sometimes it is useful while debugging another crash because of 
>> faulty
>> microcode.
>> 
> Interesting, and thanks for bringing this up.  Oleksandr, under what
> circumstances would you want to know what the old version was.  AFAICS 
> it is no
> longer running and should not have an impact on the system?

Once the kernel log does not contain a printout regarding updated 
microcode anymore (because the log buffer is limited in size and can be 
overwritten) and once you have a vmcore, it is handy to use 
boot_cpu_data to compare the microcode version with the per-CPU value to 
find out that is was updated at all. Or, maybe, that can be inspected in 
another way now?

-- 
   Oleksandr Natalenko (post-factum)