From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S932816AbeAJBrG (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Tue, 9 Jan 2018 20:47:06 -0500
Received: from Galois.linutronix.de ([146.0.238.70]:54019 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S932607AbeAJBrE (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 9 Jan 2018 20:47:04 -0500
Date: Wed, 10 Jan 2018 02:47:01 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>
cc: "Hansen, Dave" <dave.hansen@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linuxfoundation.org>,
        "x86@kernel.org" <x86@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@suse.de>,
        "Raj, Ashok" <ashok.raj@intel.com>
Subject: RE: [patch RFC 1/5] x86/CPU: Sync CPU feature flags late
In-Reply-To: <0575AF4FD06DD142AD198903C74E1CC87A571BD8@ORSMSX103.amr.corp.intel.com>
Message-ID: <alpine.DEB.2.20.1801100245010.2200@nanos>
References: <20180110010652.404145126@linutronix.de> <20180110011350.501418723@linutronix.de> <f70ea6ad-d563-5f60-2657-0551249a70e6@intel.com> <0575AF4FD06DD142AD198903C74E1CC87A571BD8@ORSMSX103.amr.corp.intel.com>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
X-Linutronix-Spam-Score: -1.0
X-Linutronix-Spam-Level: -
X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required,  ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

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