[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] A couple of HVMlite loose ends
On 13/01/16 17:03, Boris Ostrovsky wrote: > On 01/13/2016 11:30 AM, Andrew Cooper wrote: >> On 13/01/16 16:26, Jan Beulich wrote: >>>>>> On 13.01.16 at 17:17, <andrew.cooper3@xxxxxxxxxx> wrote: >>>> On 13/01/16 16:13, Jan Beulich wrote: >>>>>>>> On 13.01.16 at 16:49, <roger.pau@xxxxxxxxxx> wrote: >>>>>> Hello, >>>>>> >>>>>> While working on a HVMlite Dom0 implementation I've found a >>>>>> couple of >>>>>> loose ends with the design that I would like to comment because >>>>>> it's not >>>>>> clear to me what's the best direction to take. >>>>>> >>>>>> 1. HVM CPUID and Dom0. >>>>>> >>>>>> Sadly the way CPUID is handled inside of Xen varies between PV >>>>>> and HVM. >>>>>> On PV guests AFAICT we mostly do black-listing (I think this is the >>>>>> right term), which means we pick the native CPUID result and then >>>>>> perform a series of filter operations in order to remove features >>>>>> which >>>>>> should not be exposed to a PV guest. On the other hand, for HVM >>>>>> guests >>>>>> we pre-populate an array (d->arch.cpuids) during domain build >>>>>> time, and >>>>>> the contents of that array is what is returned to the guest when >>>>>> a CPUID >>>>>> instruction is executed. >>>>> This d->arch.cpuids[] mechanism is common to HVM and PV; the >>>>> exception really is Dom0. >>>> Dom0 is not special when it comes to cpuid, and shouldn't be >>>> treated as >>>> such. My longter term CPUID plans will be fixing this. >>> In some way it is - there's no need for hiding features from it, since >>> it can't be migrated. >> Thats perfectly fine and normal. The same applies to all other domains >> which wont migrate, or will only migrate to identical hardware. > > We don't use CPUID to only turn on and off features. It also, for > example, describes topology -- something that we may use one day > (possibly for dom0 too). It still doesn't make dom0 special compared to other guests. All guests (should) have accurate topology information represented in cpuid (I will also be fixing this). ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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