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Subject: Re: [patch RFC 1/5] x86/CPU: Sync CPU feature flags late
To: Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>
References: <20180110010652.404145126@linutronix.de>
 <20180110011350.501418723@linutronix.de>
Cc: Linus Torvalds <torvalds@linuxfoundation.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>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        Borislav Petkov <bp@suse.de>,
        "Raj, Ashok" <ashok.raj@intel.com>
From: Dave Hansen <dave.hansen@intel.com>
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Date: Tue, 9 Jan 2018 17:37:19 -0800
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On 01/09/2018 05:06 PM, Thomas Gleixner wrote:
> This is for the case where we need to set feature flags late, like, for
> example, after late microcode patch has been loaded which has enabled
> new CPUID bits.
> 
> This has no effect on alternatives patching.

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?