Re: [Xen-devel] [PATCH v2 17/23] x86/mm: put paging_update_nestedmode under CONFIG_HVM

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.09.18 at 16:27, <wei.liu2@xxxxxxxxxx> wrote:
> On Thu, Aug 30, 2018 at 02:35:37AM -0600, Jan Beulich wrote:
>> >>> On 30.08.18 at 09:42, <wei.liu2@xxxxxxxxxx> wrote:
>> > On Tue, Aug 28, 2018 at 04:50:21AM -0600, Jan Beulich wrote:
>> >> >>> On 26.08.18 at 14:19, <wei.liu2@xxxxxxxxxx> wrote:
>> >> > --- a/xen/arch/x86/mm/paging.c
>> >> > +++ b/xen/arch/x86/mm/paging.c
>> >> > @@ -919,6 +919,7 @@ const struct paging_mode *paging_get_mode(struct 
>> >> > vcpu 
>> > *v)
>> >> >      return paging_get_nestedmode(v);
>> >> >  }
>> >> >  
>> >> > +#ifdef CONFIG_HVM
>> >> >  void paging_update_nestedmode(struct vcpu *v)
>> >> >  {
>> >> >      ASSERT(nestedhvm_enabled(v->domain));
>> >> > @@ -930,6 +931,7 @@ void paging_update_nestedmode(struct vcpu *v)
>> >> >          v->arch.paging.nestedmode = NULL;
>> >> >      hvm_asid_flush_vcpu(v);
>> >> >  }
>> >> > +#endif
>> >> 
>> >> Just a consideration (no objection): Would it be worthwhile to
>> >> introduce CONFIG_NESTED_HVM at the same time (for now hard
>> >> coded to Y, and of course depending on HVM) to avoid having to
>> >> touch all such places a second time later on?
>> > 
>> > If we plan to make nested hvm configurable in the future, that would be
>> > a worthwhile thing to do; otherwise it is just another concept that
>> > users need to care about, which creates some mental burden.
>> 
>> Andrew, do you have any opinion / preference either way?
> 
> I discussed this with Andrew on IRC and came to the conclusion it is not
> worth it to introduce CONFIG_NESTED_HVM, because:
> 
> 1. Nested virt will become commonplace for Xen.
> 2. Trying to split nested parts from non-nested parts will be massively
>    complicated.

Okay then.

Jan



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