linux-kernel - Re: [RFC 05/10] x86/speculation: Add basic IBRS support infrastructure

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Date:   Wed, 24 Jan 2018 07:09:06 -0800
From:   Arjan van de Ven <arjan@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Laura Abbott <labbott@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        x86@...nel.org
Subject: Re: [RFC 05/10] x86/speculation: Add basic IBRS support
 infrastructure

On 1/24/2018 1:10 AM, Greg Kroah-Hartman wrote:
> 
>> That means the whitelist ends up basically empty right now. Should I
>> add a command line parameter to override it? Otherwise we end up having
>> to rebuild the kernel every time there's a microcode release which
>> covers a new CPU SKU (which is why I kind of hate the whitelist, but
>> Arjan is very insistent...)
> 
> Ick, no, whitelists are a pain for everyone involved.  Don't do that
> unless it is absolutely the only way it will ever work.
> 
> Arjan, why do you think this can only be done as a whitelist?

I suggested a minimum version list for those cpus that need it.

microcode versions are tricky (and we've released betas etc etc with their own numbers)
and as a result there might be several numbers that have those issues with their IBRS for the same F/M/S