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On startup, for some reason Windows 11 Hyper-V tries to set the MSR to >>>> the spec-defined initial value and since the vector is 0, it GP faults. >>>> To workaround this, treat the write as a no-op if the value is >>>> unchanged. >>>> >>>> Signed-off-by: Ross Lagerwall >>> >>> Acked-by: Jan Beulich >>> >>> I expect that despite the (valid) absence of a Fixes: tag this will want >>> backporting. >> >> It should be fine to backport, though in general I think backporting nested >> virt fixes at this point is not needed as there will be too many changes to go >> into the stable releases for it to reach a usable state. > > How is this nested-virt related? It looks to affect Win11 when run on bare- > metal Xen? The regular Windows 11 kernel doesn't have this behaviour on startup, only the Windows 11 Hyper-V kernel (and possibly other Windows versions too) so you wouldn't encounter this behaviour unless using nested-virt. Ross