Re: [PATCH 1 of 4 RFC] xen, p2m: get_entry returns level of entry as well

[Tim Deegan <tim@xen.org>]

At 16:01 +0100 on 14 Jun (1339689663), George Dunlap wrote:
> On 14/06/12 11:21, Tim Deegan wrote:
> >At 12:54 +0100 on 08 Jun (1339160091), George Dunlap wrote:
> >>Return the p2m level of the entry which filled this request.
> >>Intended to be used to see if pages returned by the balloon
> >>driver are part of a superpage, and reclaim them if so.
> >This looks broadly correct, but it's a bit invasive.  If there's any way
> >to rework patch 2 not to need it that would be helpful.  It looks like
> >the main use is for detecting and removing superpage PoD entries; maybe
> >that could be done with a sweep like you have in the non-PoD case?
> You mean the non-balloon case?  I forget why I thought that was a bad 
> idea, exactly.  Let me think about that.
> >One niggle: returning level=5 on error is non-obvious, and it doesn't
> >look like your code in patch 2 uses that.
> Were you thinking -1 or something like that?

Actually, looking at it again, and at the way the value is used by its
caller, maybe 5 is OK (though it looks like it will return 6 in the EPT
code).  So assuming this patch doesn't go away, I'd be OK with just a
comment explaining it.

Cheers,

Tim.