Re: [Xen-devel] [PATCH v4] x86/p2m: use large pages for MMIO mappings

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.01.16 at 15:05, <ian.campbell@xxxxxxxxxx> wrote:
> On Mon, 2016-01-25 at 06:54 -0700, Jan Beulich wrote:
>> > > > On 25.01.16 at 13:16, <ian.campbell@xxxxxxxxxx> wrote:
>> > On Fri, 2016-01-22 at 08:42 -0700, Jan Beulich wrote:
>> > > +#define MAP_MMIO_MAX_ITER 64 /* pretty arbitrary */
>> > > +
>> > 
>> > I suppose no existing in-tree code exceeds that (or there'd be more
>> > patch
>> > here).
>> 
>> There simply is no in-tree user other than the domctl on x86.
> 
> Right, I meant callers of the domctl (via libxc)

Then I don't understand the question. The domctl clearly can be
invoked with higher MFN counts; the #define only establishes
the cut off point for the code to return "partial success", directing
the caller to re-invoke the operation after updating inputs. I.e.
nothing else than an implementation detail which could be changed
without affecting any well behaved caller.

>> > > --- a/xen/include/public/domctl.h
>> > > +++ b/xen/include/public/domctl.h
>> > > @@ -542,8 +542,14 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_bind_
>> > >  
>> > >  
>> > >  /* Bind machine I/O address range -> HVM address range. */
>> > > -/* If this returns -E2BIG lower nr_mfns value. */
>> > >  /* XEN_DOMCTL_memory_mapping */
>> > > +/* Returns
>> > > +   - zero     (success, everything done)
>> > > +   - -E2BIG   (passed in nr_mfns value too large for the
>> > > implementation)
>> > > +   - positive (partial success, this many [less than nr_mfns] done,
>> > 
>> > Is the successful region contiguous, i.e. 0..return val, or does the
>> > caller
>> > need to figure it somehow? (I think based on libxc changes the former,
>> > but
>> > it should be spelt out here I think).
>> 
>> Yes, it is contiguous, but I'm at a loss how to spell out the (seemingly
>> obvious) fact here: "partial success, this many [less than nr_mfns]
>> initial iterations done" doesn't sound much better to me. Everything
>> else I can think of would require a full second sentence, which I
>> wouldn't like here.
> 
> I'd perhaps write "[0, result) completed successfully" or something along
> those lines.

Ah, right, that looks fine.

Thanks, Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel