[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] about fully UMIP support in Xen
>>> On 19.04.17 at 11:48, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote: > On 4/19/2017 5:18 PM, Jan Beulich wrote: >>>>> On 19.04.17 at 10:48, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote: >>> I saw that commit 8c14e5f provides emulations for UMIP affected >>> instructions. But realized that xen does not have logic to expose UMIP >>> feature to guests - you have sent out one in >>> https://lists.xenproject.org/archives/html/xen-devel/2016-12/msg00552.html >>> to emulate the cpuid leaf, but seems it was only a software solution and >>> have not get merged yet. >>> So I wonder do you have any specific plan to fully support the UMIP, >>> i.e. in Xen 4.10? :-) >> It would be nice, but I think there are caveats: While PV guests >> _shouldn't_ use any of the affected instructions, we can't blindly >> assume they don't. Hence we'd have to emulate them (producing >> to be determined data, e.g. all zeros). Luckily we don't have to >> care about VM86 mode, as for code running there emulating the >> instructions would be mandatory (as they're e.g. needed for CPU >> family detection, since the recommended approach to tell [iirc] >> 286 from 386 doesn't reliably work there). > > Thanks, Jan. > You mean if UMIP is enabled in xen, and dom0 triggers affected > instructions, 0 should > be returned? Yes. > Does hypervisor need to differentiate dom0 kernel and its > user space? If we want to para-virtualize the feature, then yes. Otherwise we can't assume the guest kernel would deal with user mode faults, so we'd have to. Arguably there could be a non-default mode in which we don't (forcing such applications to get a signal or crash). Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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