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

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Message-ID: <CALCETrX0gwkceVZpdjzej0r4SMv9U98dJ_b_KG53P9T4eynQxQ@mail.gmail.com>
Date:	Thu, 17 Sep 2015 08:17:18 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	xen-devel <Xen-devel@...ts.xen.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops

On Sep 17, 2015 5:33 AM, "Peter Zijlstra" <peterz@...radead.org> wrote:
>
> 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 :-)

I was taking about QEMU TCG, not KVM.


--Andy
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