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[Xen-devel] RE: [PATCH] CPUID level 0x00000007:0 (ebx) is word 9, instea

To: Keir Fraser <keir.xen@xxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: [Xen-devel] RE: [PATCH] CPUID level 0x00000007:0 (ebx) is word 9, instead of word 7
From: "Li, Xin" <xin.li@xxxxxxxxx>
Date: Wed, 1 Jun 2011 22:41:07 +0800
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Thread-topic: [PATCH] CPUID level 0x00000007:0 (ebx) is word 9, instead of word 7
> >>>> On 31.05.11 at 16:59, "Li, Xin" <xin.li@xxxxxxxxx> wrote:
> >>> can't see why we would need to stay in sync with Linux's capability
> >>> array indices.
> >>
> >> why?  Typically we reuse Linux code unless Xen has its special logic.
> >
> > So you would suggest leaving indices 7 and 8 unused instead?
> > Looking at current Linux, we certainly could convert Xen to use
> > index 8 for virtualization features, but since these are being
> > tracked differently already anyway I don't see a value in this.
> >
> > As to index 7, just look at ARAT - we're already diverging from
> > Linux here (having it allocated in index 3).
> >
> > Bottom line is that I think keeping the names (and in various cases
> > the grouping together, namely when the bits are grouped together
> > in some CPUID leaf's output) in sync is desirable, but following
> > Linux to the bit doesn't always make sense. After all, some thinking
> > will always be necessary when porting over patches.
> Agreed.

Okay, I raised this because I saw 2 bugs coming from the differences
between Xen and Linux.  Anyway let's keep in mind that we should 
refer to Linux design and code to save some effort and reduce bugs.

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