Re: [PATCH v3 3/3] tools: introduce parameter max_wp_ram_ranges.

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: George Dunlap [mailto:george.dunlap@citrix.com]
> Sent: 17 February 2016 11:02
> To: Jan Beulich; Paul Durrant; Kevin Tian; Zhang Yu
> Cc: Andrew Cooper; Ian Campbell; Ian Jackson; Stefano Stabellini; Wei Liu;
> Zhiyuan Lv; xen-devel@lists.xen.org; George Dunlap; Keir (Xen.org)
> Subject: Re: [Xen-devel] [PATCH v3 3/3] tools: introduce parameter
> max_wp_ram_ranges.
> 
> On 17/02/16 10:22, Jan Beulich wrote:
> >>>> On 17.02.16 at 10:58, <kevin.tian@intel.com> wrote:
> >> Thanks for the help. Let's see whether we can have some solution ready
> for
> >> 4.7. :-)
> >
> > Since we now seem to all agree that a different approach is going to
> > be taken, I think we indeed should revert f5a32c5b8e ("x86/HVM:
> > differentiate IO/mem resources tracked by ioreq server"). Please
> > voice objections to the plan pretty soon.
> 
> FWIW, after this discussion, I don't have an objection to the basic
> interface in this series as it is, since it addresses my request that it
> be memory-based, and it could be switched to using p2m types
> behind-the-scenes -- with the exception of the knob to control how many
> ranges are allowed (since it exposes the internal implementation).
> 
> I wouldn't object to the current implementation going in as it was in v9
> (apparently), and then changing the type stuff around behind the scenes
> later as an optimization.  I also don't think it would be terribly
> difficult to change the implementation as it is to just use write_dm for
> a single IOREQ server.  We can rename it ioreq_server and expand it
> later.  Sorry if this wasn't clear from my comments before.
>

The problem is that, since you objected to wp_mem being treated the same as mmio, we had to introduce a new range type to the map/unmap hypercalls and that will become redundant if we steer by type. If we could have just increased the size of the rangeset for mmio and used that *for now* then weeks of work could have been saved going down this dead end.

  Paul
 
> A new interface that's been carefully thought through would of course be
> nice too.
> 
>  -George