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

From: Ingo Molnar
Date: Tue Jun 09 2009 - 11:16:21 EST

* Harald Welte <HaraldWelte@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> >
> > 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.

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