linux-kernel - Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and MSR_IA32_PRED

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Message-ID: <91d41f66-d744-e8b0-89f0-a167d3a3918c@redhat.com>
Date:   Wed, 10 Jan 2018 15:28:43 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Arjan van de Ven <arjan@...ux.intel.com>,
        Nadav Amit <nadav.amit@...il.com>
Cc:     Liran Alon <liran.alon@...cle.com>, jmattson@...gle.com,
        x86@...nel.org, dwmw@...zon.co.uk, bp@...en8.de,
        aliguori@...zon.com, thomas.lendacky@....com, rkrcmar@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and
 MSR_IA32_PRED_CMD down to the guest

On 10/01/2018 15:06, Arjan van de Ven wrote:
> On 1/10/2018 5:20 AM, Paolo Bonzini wrote:
>> * a simple specification that does "IBRS=1 blocks indirect branch
>> prediction altogether" would actually satisfy the specification just as
>> well, and it would be nice to know if that's what the processor actually
>> does.
> 
> it doesn't exactly, not for all.
> 
> so you really do need to write ibrs again.

Okay, so "always set IBRS=1" does *not* protect against variant 2.  Thanks,

Paolo