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

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Message-ID: <alpine.DEB.2.21.1909161227060.10731@nanos.tec.linutronix.de>
Date:   Mon, 16 Sep 2019 12:36:11 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Raj, Ashok" <ashok.raj@...el.com>
cc:     Johannes Erdfelt <johannes@...felt.com>,
        Borislav Petkov <bp@...en8.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Mihai Carabas <mihai.carabas@...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,
        Tom Lendacky <thomas.lendacky@....com>,
        x86-ml <x86@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/microcode: Add an option to reload microcode even
 if revision is unchanged

On Sat, 7 Sep 2019, Thomas Gleixner wrote:
> On Fri, 6 Sep 2019, Raj, Ashok wrote:
> > On Fri, Sep 06, 2019 at 11:16:00PM +0200, Thomas Gleixner wrote:
> > > Now #1 is actually a sensible and feasible solution which can be pulled off
> > > in a reasonably short time frame, avoids all the bound to be ugly and
> > > failure laden attempts of fixing late loading completely and provides a
> > > usable and safe solution for joe user, jack admin and the super experts at
> > > big-cloud corporate.
> > > 
> > > That is not requiring any new format of microcode payload, as this can be
> > > nicely done as a metadata package which comes with the microcode
> > > payload. So you get the following backwards compatible states:
> > > 
> > >   Kernel  metadata	  result
> > > 
> > >   old	  don't care	  refuse late load
> > > 
> > >   new	  No   		  refuse late load
> > > 
> > >   new	  Yes		  decide based on metadata
> > > 
> > > Thoughts?
> > 
> > This is 100% in line with what we proposed... 
> 
> So what it hindering you to implement that? ucode teams whining about the
> little bit of extra work?

That said, there is also a distinct lack of information about micro code
loading in a safe way in general. We absolutely do not know whether a micro
code update affects any instruction which might be in use during the update
on a sibling. Right now it's all load and pray and the SDM is not really
helpful with that either.

Thanks,

	tglx