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Message-ID: <1517257022.18619.30.camel@infradead.org>
Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support
 infrastructure
From:   David Woodhouse <dwmw2@infradead.org>
To:     Eduardo Habkost <ehabkost@redhat.com>,
        KarimAllah Ahmed <karahmed@amazon.de>
Cc:     linux-kernel@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Laura Abbott <labbott@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
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        Tim Chen <tim.c.chen@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>, kvm@vger.kernel.org,
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Date:   Mon, 29 Jan 2018 20:17:02 +0000
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On Mon, 2018-01-29 at 18:14 -0200, Eduardo Habkost wrote:
>=20
> Sorry for being confused here, as probably the answer is buried
> on a LKML thread somewhere.=C2=A0 The comment explains what the code
> does, but not why.=C2=A0 Why exactly IBRS is preferred on Skylake?
>=20
> 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.=C2=A0 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=C2=A0should cover most of that, I think=
.
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