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RE: [Xen-devel] [PATCH] Fix build failure in 32 environment

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] Fix build failure in 32 environment
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Mon, 14 Dec 2009 10:22:52 -0800 (PST)
Cc: "Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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> >> It can be supported for existign features but not all new 
> ones. We can
> >> perhaps retire it all together after 4.0.
> > 
> > IMHO, this is not a new feature, this is an ABI incompatibility
> > issue. If rdtscp is a valid 32-bit instruction, IMHO it
> > should either work on both 32-bit Xen and 64-bit Xen or
> > neither.
> It only needs to work if we advertise RDTSCP in CPUID. Which 
> we don't for
> 32-bit hosts. There's really nothing wrong with the patch 
> that I can see.
> I'd rather have the CPUID frobbing in xc_cpuid_x86.c, but it's a minor
> concern. 

An application should be able to check the CPUID bit once and assume
that it doesn't change.

If live migration and save/restore don't work between a 32-bit
Xen and a 64-bit Xen, you are technically correct.  This
is true of the open source xm tools, but I don't know that
it is true of all distro toolsets.

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