linux-kernel - RE: [v2 1/3] x86/microcode/intel: Check microcode revision before updating sibling threads

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Date:   Thu, 22 Feb 2018 15:49:05 +0000
From:   "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
To:     Henrique de Moraes Holschuh <hmh@....eng.br>,
        "Raj, Ashok" <ashok.raj@...el.com>
CC:     Borislav Petkov <bp@...e.de>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...nel.org>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: RE: [v2 1/3] x86/microcode/intel: Check microcode revision before
 updating sibling threads


> > In the past the only guidance was to not load microcode at the same time to
> the
> > thread siblings of a core. We now have new guidance that the sibling must be
> > spinning and not doing other things that can introduce instability around
> loading
> > microcode.
> 
> Document that properly in the Intel SDM, *please*.

yes we will update the SDM, just that is a much longer process than sending code out.

> 
> While at it, please verify with the microcode teams that the requirement
> for 16-byte alignment of the microcode update as present in the Intel
> SDM still stands.  

I'd be surprised if it did not. 

>Linux does not enforce it on the early microcode
> update loader when using an initramfs (but userspace can work around
> that, and iucode_tool --early-fw does so).  If that 16-byte alignment is
> important, I could dust off some patches that fix it.

hmm wonder what those tools do nowadays; Intel publishes the microcode in the linux native format since some time (and the .dat format is about to go away entirely)