Re: [Xen-devel] [PATCH RFC] xen: arm: use uncached foreign mappings when building guests

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-01-02 at 15:10 +0000, David Vrabel wrote:
> > We basically only support guests running without caches at start of day.
> > We expect and require them to come up and enable caches and then keep
> > them enabled. Fortunately this is normal practice...
> 
> There is still a (small) window where a guest is running with caches
> disabled and it may be saved/migrated at this point.  Is this a concern?

I don't think so, if nothing else while the guest has caches disabled it
is so early that it is mostly certainly not watching the xenbus control
node.

I suppose we might theoretically start a live migration right after boot
and iterate until caches were enabled, but with stale pages in the save
image (those which didn't change since boot).

There's a large dollop of "don't do that then" but probably the
migration code should check that caches are enabled as one of the first
things it does.

Ian.


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