Messages in this thread |  | | | Date | Sun, 15 Mar 2009 11:45:53 -0700 | | From | "H. Peter Anvin" <> | | Subject | Re: [Xen-devel] [PATCH 10/24] xen: mask XSAVE from cpuid |
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Jeremy Fitzhardinge wrote: > Jan Beulich wrote: >> As pointed out on an earlier thread, it seems inappropriate to do probing >> like this when there is a cpuid feature flag (osxsave) that can be >> used to >> determine whether XSAVE can be used. And even without that flag, >> simply reading CR4 and checking whether osxsave is set there would >> suffice. This is under the assumption that Xen's to-be-done >> implementation >> of XSAVE support would match that of FXSAVE (Xen turns its support on >> unconditionally and for all [pv] guests). > > I didn't want to make too many assumptions about how Xen's XSAVE support > would look. In particular, I thought it might virtualize the state of > OSXSAVE to give the guest the honour of appearing to enable it. A guest > kernel may get confused if it starts with OSXSAVE set, as it may use it > to control its own init logic.
That wouldn't be an issue if you use the *native* CPUID to look for OSXSAVE early on, since such virtualization would only be visible though the PV interface, right?
It seems cleaner than probing, to be sure...
-hpa
-- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
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