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

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Message-ID: <alpine.DEB.2.20.1801100245010.2200@nanos>
Date:   Wed, 10 Jan 2018 02:47:01 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
cc:     "Hansen, Dave" <dave.hansen@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        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

On Wed, 10 Jan 2018, Van De Ven, Arjan wrote:
> > 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)

That stuff indeed would be way simpler w/o the late support, but the fact
that the microcode for this might reach the user way later than the kernel
support makes it almost a must to support the late loading.

Thanks,

	tglx