From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support
 infrastructure
Date: Mon, 29 Jan 2018 12:44:16 -0800
Message-ID: <31415b7f-9c76-c102-86cd-6bf4e23e3aee@linux.intel.com>
References: <1516476182-5153-6-git-send-email-karahmed@amazon.de>
 <20180129201404.GA1588@localhost.localdomain>
 <1517257022.18619.30.camel@infradead.org>
 <20180129204256.GV25150@localhost.localdomain>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Cc: KarimAllah Ahmed <karahmed@amazon.de>,
        linux-kernel@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        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>,
To: Eduardo Habkost <ehabkost@redhat.com>,
        David Woodhouse <dwmw2@infradead.org>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20180129204256.GV25150@localhost.localdomain>
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

On 1/29/2018 12:42 PM, Eduardo Habkost wrote:
> The question is how the hypervisor could tell that to the guest.
> If Intel doesn't give us a CPUID bit that can be used to tell
> that retpolines are enough, maybe we should use a hypervisor
> CPUID bit for that?

the objective is to have retpoline be safe everywhere and never use IBRS
(Linus was also pretty clear about that) so I'm confused by your question