linux-kernel - Re: [PATCH] x86/microcode: Add an option to reload microcode even if revision is unchanged

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Message-ID: <20190829130213.GA23510@araj-mobl1.jf.intel.com>
Date:   Thu, 29 Aug 2019 06:02:14 -0700
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Mihai Carabas <mihai.carabas@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jon Grimm <Jon.Grimm@....com>, kanth.ghatraju@...cle.com,
        konrad.wilk@...cle.com, patrick.colp@...cle.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        x86-ml <x86@...nel.org>, linux-kernel@...r.kernel.org,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH] x86/microcode: Add an option to reload microcode even if
 revision is unchanged

On Thu, Aug 29, 2019 at 08:09:42AM +0200, Borislav Petkov wrote:
> On Wed, Aug 28, 2019 at 10:33:22PM -0700, Ashok Raj wrote:
> > During microcode development, its often required to test different versions
> > of microcode. Intel microcode loader enforces loading only if the revision is
> > greater than what is currently loaded on the cpu. Overriding this behavior
> > allows us to reuse the same revision during development cycles.
> > This facilty also allows us to share debug microcode with development
> > partners for getting feedback before microcode release.
> > 
> > Microcode developers should have other ways to check which
> > of their internal version is actually loaded. For e.g. checking a
> > temporary MSR for instance. In order to reload the same microcode do as
> > shown below.
> > 
> >  # echo 2 > /sys/devices/system/cpu/microcode/reload
> > 
> >  as root.
> > 
> > 
> > I tested this on top of the parallel ucode load patch
> > 
> > https://lore.kernel.org/r/1566506627-16536-2-git-send-email-mihai.carabas@oracle.com/
> > 
> > v2: [Mihai] Address comments from Boris
> > 	- Support for AMD
> > 	- add taint flag
> > 	- removed global force_ucode_load and parameterized it.
> 
> As I've said before, I don't like the churn in this version and how it
> turns out. I'll have a look at how to do this cleanly when I get some
> free cycles.

Thanks Boris. I'll wait for your updates. I remember your comment on another
simplification from the Boris Ostrovsky https://lore.kernel.org/r/20190828191618.GO4920@zn.tnic/

Mihai rolled in your suggestions noted above.

BTW, We only need to force on the late-load. Its not needed during early load.

Cheers,
Ashok