Re: [PATCH V2] Add flag to start info regarding virtual mapped p2m list

[Ian Campbell <ian.campbell@citrix.com>]

On Wed, 2015-03-18 at 11:59 +0100, Juergen Gross wrote:

> > Is there not an ABI change somewhere else relating to the exposure of
> > the cr3+vaddr+size? If so why is it not in this patch?
> 
> Commit 50bd1f0825339dfacde471df7664729216fc46e3
> 
> > Ideally whichever file which needs to change in xen/include/public to
> > expose that change should also come along with documentation for this
> > new ABI.
> 
> Included in above commit in form of comments in the modified file.

Great, please mention in the commit log here that this is building on
that work (would have saved me having to ask).

> > If that change has been deferred for some reason then I think it (and
> > why) should be mentioned in the commit message, you'll also want to
> > explain why adding the bit now but the ABI change later is safe, i.e.
> > what the transition plan is.
> >
> > AIUI this change has broken memory hotplug and has also made it
> > difficult from an ABI PoV to reinstate that support. I think that needs
> > to be addressed (i.e. at the ABI design level, not necessary
> > implemented) before we add a bit exposing this feature.
> 
> The interface change didn't brake anything. It was the implementation in
> the Linux kernel.

AIUI the new interface has made it difficult to for OS kernels to
arrange to be able to grow their P2M. Whether that is an "OS kernel
issues" or an "interface issue" isn't really the point, the fact is that
for whatever reason it is now difficult to arrange.

Is there a plan for how this might be dealt with?

Ian.