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

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Date:   Mon, 29 Jan 2018 20:17:02 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Eduardo Habkost <ehabkost@...hat.com>,
        KarimAllah Ahmed <karahmed@...zon.de>
Cc:     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>,
        Peter Zijlstra <peterz@...radead.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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 Mon, 2018-01-29 at 18:14 -0200, Eduardo Habkost wrote:
> 
> Sorry for being confused here, as probably the answer is buried
> on a LKML thread somewhere.  The comment explains what the code
> does, but not why.  Why exactly IBRS is preferred on Skylake?
> 
> I'm asking this because I would like to understand the risks
> involved when running under a hypervisor exposing CPUID data that
> don't match the host CPU.  e.g.: what happens if a VM is migrated
> from a Broadwell host to a Skylake host?

https://lkml.org/lkml/2018/1/22/598 should cover most of that, I think.
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