Re: [Xen-devel] [PATCH RFC v1 45/74] x86/guest: use unpopulated memory to map the shared_info page

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.01.18 at 12:06, <roger.pau@xxxxxxxxxx> wrote:
> On Mon, Jan 08, 2018 at 04:03:50AM -0700, Jan Beulich wrote:
>> >>> On 04.01.18 at 14:05, <wei.liu2@xxxxxxxxxx> wrote:
>> > This prevents hardcoding a known unpopulated memory page to map
>> > the shared info page. This fixes a TODO item in a previous patch.
>> > 
>> > Remove hypervisor_early_setup as now it is not required anymore.
>> > 
>> > Signed-off-by: Roger Pau Monne <roger.pau@xxxxxxxxxx>
>> > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
>> 
>> Looks good, but one question:
>> 
>> > @@ -187,15 +186,12 @@ static void __init init_memmap(void)
>> >      }
>> >  }
>> >  
>> > -void __init hypervisor_early_setup(struct e820map *e820)
>> > -{
>> > -    map_shared_info(e820);
>> > -}
>> > -
>> >  void __init hypervisor_setup(void)
>> >  {
>> >      init_memmap();
>> >  
>> > +    map_shared_info();
>> > +
>> >      init_evtchn();
>> >  }
>> 
>> If the shared info page isn't needed as early, why was it set up
>> that early originally?
> 
> Because during the setup of the shared_info the used memory address
> would also be added to the e820 in order to mark it as RAM. I don't
> think that was really required, since it's not needed to have a
> page_info for the shared_info because it's not shared with the guest.

Ah, I see.

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


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