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Re: [Xen-devel] DomU crash during migration when suspendingsource domain

  • To: "Graham, Simon" <Simon.Graham@xxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir@xxxxxxxxxxxxx>
  • Date: Wed, 14 Feb 2007 14:35:41 +0000
  • Delivery-date: Wed, 14 Feb 2007 06:35:03 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdP6h4+HveIAzruQ3+gt7NQNapEGwANqzaeAADJUVAAAHIl2wAGcwGgAAF4ck4=
  • Thread-topic: [Xen-devel] DomU crash during migration when suspendingsource domain

In general we *cannot* expect to support CPUs with different features in
CPUID. We plan to fix this in two ways:
 1. Allow a guest to be given a restricted CPUID view (e.g., with features
masked out, or cacheinfo leaves missing).
 2. Where a guest has been exposed to extended features and leaves, prevent
it from being migrated to a less-capable CPU.

A further option (3) for cache info might be to fake out the leaves for CPUs
that do not support them. But I'm not sure whether, for example, this would
be compatible with AMD's CPUID instruction.

This issue is hardly specific to HA/FT. You can safely build yourself a
HA/FT cluster out of homogeneous hardware. Building it out of odds and ends
you have already is going to be hard or impossible to guarantee safety of in
general. I don't believe anyone sells or supports software to allow you to
do this, and there's a reason for that.

 -- Keir

On 14/2/07 13:57, "Graham, Simon" <Simon.Graham@xxxxxxxxxxx> wrote:

> I think this is indeed what is happening -- supporting this is kind of
> important for HA/FT - you need to be able to keep the domains running
> when upgrading/replacing hardware.
> I guess I'm still a tad confused, but presumably the CPU_DEAD processing
> is not completely uninitializing the cache info (it seems to me that if
> it discarded the cache info and NULL's the pointer in the CPU_DEAD
> processing then it should get recreated when the CPU_ONLINE is done -
> presumably there is some path where this is not done when it should be.
> I'll do some more digging and get back with a proposed fix.

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