Re: [XenPPC] Re: [Xen-ia64-devel] [PATCH 1/2] remove xencomm page size limit(xen side)

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Thu, Aug 02, 2007 at 10:00:46AM -0500, Hollis Blanchard wrote:
> On Thu, 2007-08-02 at 11:44 +0900, Isaku Yamahata wrote:
> > 
> > > But we can issue sequential p2m hcalls with different offsets, so we
> > do.
> > > So what exactly is the new problem?
> > 
> > The limit is about 64GB for xen/ia64 because xen/ia64 deafult page
> > size
> > is 16KB.
> > The issue I'm seeing is the populate physmap hypercall failure
> > at domain creation. It's essentially same issue you described above.
> > I want to remove the limitation with the patches. 
> 
> Can't you simply issue repeated populate_physmap hypercalls,
> incrementing extent_start?

Yes, it's possible. However my choice was to generalize xencomm
because 
  - The inline xencomm code already supports page boundary crossing.
  - IMHO it doesn't unnecessarily complicate the existing code.
  - Anyway struct xencomm_desc page boundary crossing check should
    be done because a hostile guest can pass such a pointer.
    Without the check, xencomm code may access first 4bytes of
    the unrelated page as desc->nr_addrs.

If you are reluctant to patch xencomm code because of testing,
how about, consolidate xencomm code at first, next test the patch
with xen/ia64, then merge the patch?
Or do you have any other reason?

-- 
yamahata

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