[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 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). For HVM guests the feature is of no interest to Xen itself anyway, i.e. all we'd need is allow them to enable the CR4 bit (which my emulation patch did as a side effect, but that patch has been deferred until after Andrew manages to put in some more CPUID work; that single hunk could certainly be split out if desired). Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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