linux-kernel - RE: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future CPUs

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Date:   Tue, 20 Feb 2018 00:00:23 +0000
From:   "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
To:     "valdis.kletnieks@...edu" <valdis.kletnieks@...edu>
CC:     Jon Masters <jcm@...masters.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Ingo Molnar" <mingo@...nel.org>
Subject: RE: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future
 CPUs


> On Mon, 19 Feb 2018 23:42:24 +0000, "Van De Ven, Arjan" said:
> 
> > the guest is not the problem; guests obviously will already honor if Enhanced
> > IBRS is enumerated. The problem is mixed migration pools where the
> hypervisor
> > may need to decide to not pass this enumeration through to the guest.
> 
> For bonus points:  What should happen to a VM that is live migrated from one
> hypervisor to another, and the hypervisors have different IBRS support?

Doctor Doctor it hurts when I do this....

Migration tends to only work between HV's that are relatively homogeneous, that's nothing new... folks who run clouds or bigger pools know this obviously.