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Subject: Re: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future
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To:     David Woodhouse <dwmw2@infradead.org>, tglx@linutronix.de,
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From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <b55a1e8a-a70f-b007-e4d7-6864d7bdd683@redhat.com>
Date:   Tue, 13 Feb 2018 11:55:52 +0100
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On 13/02/2018 11:53, David Woodhouse wrote:
>> You have my vote. :)  Really, IBRS_ALL makes no sense and it would be
>> nice to know _why_ Intel is pushing something that makes no sense.
> No, IBRS_ALL *does* make sense. It's not a complete fix, but it's as
> much of a fix as they should shoe-horn into the generation of CPUs
> which are currently going to the fabs.
> 
> With IBRS_ALL they presumably add tags to the predictions with the VMX
> mode and ring, to give complete protection against predictions being
> used in a more privileged mode. 

Yeah, but I still don't get why they need an MSR to turn those tags on.
Is it basically a chicken bit in the wrong direction?

Paolo