Subject: Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and
 MSR_IA32_PRED_CMD down to the guest
To: Arjan van de Ven <arjan@linux.intel.com>,
        Nadav Amit <nadav.amit@gmail.com>
Cc: Liran Alon <liran.alon@oracle.com>, jmattson@google.com,
        x86@kernel.org, dwmw@amazon.co.uk, bp@alien8.de,
        aliguori@amazon.com, thomas.lendacky@amd.com, rkrcmar@redhat.com,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
References: <222d0a6b-820f-4d7c-a616-ac89f77c3c09@default>
 <834e9b46-5d59-a81e-8cda-5f576964e1cb@redhat.com>
 <EBDECE05-48A1-4906-AC0D-8D5928A799F2@gmail.com>
 <c31716da-a3d1-35e9-7671-8b8b80a5879e@redhat.com>
 <9360a280-228d-26d9-5561-6688aa67881c@linux.intel.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <91d41f66-d744-e8b0-89f0-a167d3a3918c@redhat.com>
Date: Wed, 10 Jan 2018 15:28:43 +0100
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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