Re: [Xen-devel] 3.2 and later compatibility issue

[John Levon <levon@xxxxxxxxxxxxxxxxx>]

On Tue, Mar 11, 2008 at 06:21:36PM +0000, Keir Fraser wrote:

> > "Strictly speaking we're not changing Xen's heap mappings. The issue
> > is that we are creating new mappings to Xen heap pages that have
> > not full caching attributes. Intel says that all mappings to a given
> > page should use the same caching attributes. It appears that Xen
> > is now enforcing that with a check."
> > 
> > This is a fairly nasty compatibility issue, but then, Solaris is "wrong"
> > in trying to add the mappings as they are. Is there a sensible way to
> > fix this breakage in Xen?
> 
> Xen could silently re-set the PAT flags in the PTE, rather than fail the PTE
> update completely. I'm fearful that just stores up trouble for future
> though, by reducing bug visibility. Also the guest may not like having its
> PTEs mangled in this way. And, since this is a workaround for old guests,
> we'd have to make this distasteful behaviour the default!

It looks like we're just going to eat the incompatibility on this one.

regards
john

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