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

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Message-ID: <55FADD25.6040909@citrix.com>
Date:	Thu, 17 Sep 2015 16:32:53 +0100
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	Borislav Petkov <bp@...en8.de>, Paolo Bonzini <pbonzini@...hat.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	KVM list <kvm@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	xen-devel <Xen-devel@...ts.xen.org>,
	Andy Lutomirski <luto@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Arjan van de Ven" <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [Xen-devel] [PATCH 0/3] x86/paravirt: Fix baremetal paravirt
 MSR ops

On 17/09/15 16:27, Borislav Petkov wrote:
> On Thu, Sep 17, 2015 at 01:39:26PM +0200, Paolo Bonzini wrote:
>> That's not a big deal, that's what *_safe is for.  The problem is that
>> there are definitely some cases where the *_safe version is not being used.
> I mean to do feature checks which assure you that those MSRs are
> there so you don't need the safe variants. And that is not always
> easy/possible.
>

There are plenty of non-architectural MSRs in use which don't have
feature bits.

Xen used to have problems booting when using the masking MSRs when
booting virtualised.  Nowadays it uses a cpu vendor check and _safe()
probe to detect support.

~Andrew
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