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

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Date:   Wed, 24 Jan 2018 12:58:59 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     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>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "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 Wed, 2018-01-24 at 13:29 +0100, Peter Zijlstra wrote:
> 
> Yes :/
> 
> We could look at extending x86_cpu_id and x86_match_cpu with a stepping
> option I suppose, but that might be lots of churn.

That goes all the way to mod_deviceinfo, and would be horrid.

We could add an x86_match_cpu_stepping() function, I suppose? But I'm
mostly trying to avoid depending on other stuff like that, for patches
which are going to need to be backported to all the stable kernels.

I'd much rather do it this way and then if we see another use case for
it (that commit you mentioned could be nicer, I suppose), consolidate
into a single stepping-capable lookup function in a later "cleanup".
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