linux-kernel - Re: [PATCH] X86: cpu_debug support for VIA / Centaur CPU's

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Message-ID: <20090609151557.GA9362@elte.hu>
Date:	Tue, 9 Jun 2009 17:15:57 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Harald Welte <HaraldWelte@...tech.com>
Cc:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [PATCH] X86: cpu_debug support for VIA / Centaur CPU's


* Harald Welte <HaraldWelte@...tech.com> wrote:

> Thanks for your quick response.
> 
> On Tue, Jun 09, 2009 at 02:23:18PM +0530, Jaswinder Singh Rajput wrote:
>  
> > On Tue, 2009-06-09 at 16:29 +0800, Harald Welte wrote:
> > > This patch adds the MSR definitions for the VIA/Centaur CPU models
> > > to cpu_debug.c
> > > 
> > > Signed-off-by: Harald Welte <HaraldWelte@...tech.com>
> > 
> > As per Ingo suggestion, we removed model information from cpu_debug and
> > is available in -tip :
> 
> but what happens if one MSR has a different group from vendor A to 
> vendor B? [...]

MSRs should really be enumerated along CPU features. They will be 
accessed if a CPU offers that CPU feature.

> [...] and what happens if you read MSR's on a CPU that doesn't 
> have them?  I suppose you get a segmentation fault, at least 
> that's what I've received in the past when accidentially reading a 
> MSR that doesn't exist.  Is that what the _safe_ variant of rdmsr 
> is for?

Yeah, the safe read should never fault - there should be all zeroes 
or an error return.

	Ingo
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