linux-kernel - Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops

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Message-ID: <20150917122750.GH3604@twins.programming.kicks-ass.net>
Date:	Thu, 17 Sep 2015 14:27:50 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
	KVM list <kvm@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	xen-devel <Xen-devel@...ts.xen.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops

On Thu, Sep 17, 2015 at 01:40:30PM +0200, Paolo Bonzini wrote:
> 
> 
> On 17/09/2015 10:58, Peter Zijlstra wrote:
> > But the far greater problem I have with the whole virt thing is that
> > you cannot use rdmsr_safe() to probe if an MSR exists at all because, as
> > you told me, these virt thingies return 0 for all 'unknown' MSRs instead
> > of faulting.
> 
> At least for KVM, that behavior is opt-in (the ignore_msrs parameter)
> and no distro that I know enables it by default.

Ah, that would be good news. Andy earlier argued I could not rely on
rdmsr_safe() faulting on unknown MSRs. If practically we can there's
some code I can simplify :-)
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