[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] about fully UMIP support in Xen
On 4/19/2017 7:19 PM, Jan Beulich wrote: 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). Thanks, Jan.For UMIP is to be para-virtualized, is it OK to give dom0 kernel the physical value if instructions are triggered in the kernel?And if the instructions are triggered in dom0 user space, the spec requires a #GP fault, and we can return 0 to the application in the #GP fault handler, is it OK? Yu Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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