linux-kernel - RE: [patch RFC 1/5] x86/CPU: Sync CPU feature flags late

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Date:   Wed, 10 Jan 2018 01:39:19 +0000
From:   "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
To:     "Hansen, Dave" <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
CC:     Linus Torvalds <torvalds@...uxfoundation.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Andi Kleen" <ak@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Andy Lutomirski" <luto@...nel.org>, Borislav Petkov <bp@...e.de>,
        "Raj, Ashok" <ashok.raj@...el.com>
Subject: RE: [patch RFC 1/5] x86/CPU: Sync CPU feature flags late

 
> In other words, if you use late microcode loading for getting IBRS, you
> don't get ALTERNATIVE patching and its benefits?
> 
> I'll also profess some microcode ignorance here.  Is "late microcode
> patching" *all* of the stuff we do from the OS, or do we have early and
> late Linux loading in addition to what the BIOS can do?

the early boot loader level stuff is much better generally (but does not work when the microcode comes out after the system booted... like really long uptimes)