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

["Graham, Simon" <Simon.Graham@xxxxxxxxxxx>]

> 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).

Do you plan to do this for PV domains as well as HVM?

>  2. Where a guest has been exposed to extended features and leaves,
> prevent
> it from being migrated to a less-capable CPU.
> 

I guess I'm not quite sure I fully understand -- since we hot remove all
the processors (but one - I guess that is an issue) and then hot add
them again after migration, you would think it would be OK to hot add a
completely different processor -- of course there will be issues with
the Linux code given that you cant actually test this on a
non-virtualized system.

> 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.
> 

Agreed.

> 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.

You misunderstand my point -- in an FT environment, you MUST be able to
upgrade and repair hardware without taking the domain down -- clearly
this would normally be to an equivalent or higher functionality system
but we cant guarantee that there wont be a new spiffy processor that
causes this same issue to arise or that we wont run into some similar
issue when replacing faulty hardware (the original system might no
longer be available for example).

Simon


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