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Roger Pau Monné
0570d7f276
Introduce an option to allow selecting a behavior similar to the pre Xen 4.15 one for accesses to MSRs not explicitly handled. Since commit84e848fd7aand322ec7c89faccesses to MSRs not explicitly handled by Xen result in the injection of a #GP to the guest. This is a behavior change since previously a #GP was only injected if accessing the MSR on the real hardware would also trigger a #GP, or if the attempted to be set bits wouldn't match the hardware values (for PV). The reasons for not leaking hardware MSR values and injecting a #GP are fully valid, so the solution proposed here should be considered a temporary workaround until all the required MSRs are properly handled. This seems to be problematic for some guests, so introduce an option to fallback to this kind of legacy behavior without leaking the underlying MSR values to the guest. When the option is set, for both PV and HVM don't inject a #GP to the guest on MSR read if reading the underlying MSR doesn't result in a #GP, do the same for writes and simply discard the value to be written on that case. Note that for guests restored or migrated from previous Xen versions the option is enabled by default, in order to keep a compatible MSR behavior. Such compatibility is done at the libxl layer, to avoid higher-level toolstacks from having to know the details about this flag. Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> Acked-by: Christian Lindig <christian.lindig@citrix.com> Reviewed-by: Ian Jackson <iwj@xenproject.org> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com> Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com> Release-Acked-by: Ian Jackson <iwj@xenproject.org>