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Re: [Xen-devel] address space reorganization

To: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] address space reorganization
From: Jacob Gorm Hansen <jacobg@xxxxxxx>
Date: Wed, 13 Apr 2005 20:08:00 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Gerd Knorr <kraxel@xxxxxxxxxxx>
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Ian Pratt wrote:

That works OK for the kernel, but you might have user space apps that
have adapted their behviour based on what the've found in /proc/cpuinfo.

A compromise then would be to lie to userspace and still recalibrate the kernel.

A particularly nasty case is apps or libraries that go at 'cpuid'
directly, as we can't trap that instruction. I guess VMware have the
same problem, as I don't believe they translate ring 3 code.

Yeah, nothing we can do there really, except tell people not to :-(

As regards your proposed critical region, we already effectively do
this.  We don't recalibrate stuff after a migration yet though (some of
the tests are quite slow, so I'm not sure you'd want to do them all
anyhow).

Could perhaps do them in advance, or during the pre-copy phase as they are likely to stay constant for the lifetime of the machine, but that demands that the receiving side knows what you are looking for. My system uploads a bootstrapper to the target VM in advance, so I could have this info ready when the rest of the OS arrives.

Jacob


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