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

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Message-ID: <9360a280-228d-26d9-5561-6688aa67881c@linux.intel.com>
Date:   Wed, 10 Jan 2018 06:06:59 -0800
From:   Arjan van de Ven <arjan@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.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 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.