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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 11/3/08 18:05, "John Levon" <levon@xxxxxxxxxxxxxxxxx> 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!

 -- Keir



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