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Re: [Xen-devel] [PATCH v3 5/6] ioreq-server: add support for multiple servers

  • To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
  • From: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
  • Date: Tue, 18 Mar 2014 11:33:14 +0000
  • Accept-language: en-GB, en-US
  • Cc: "xen-devel@xxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxx>
  • Delivery-date: Tue, 18 Mar 2014 11:33:39 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>
  • Thread-index: AQHPOIHtl/Hs0EZRYkOvPLk7jZi8g5rgde+AgATKvVD///hXAIAAEWgA///zsYCAAB/kwP///vCAAAI7FwD///FegP/+mgYg
  • Thread-topic: [Xen-devel] [PATCH v3 5/6] ioreq-server: add support for multiple servers

> -----Original Message-----
> From: Ian Campbell
> Sent: 17 March 2014 14:56
> To: Paul Durrant
> Cc: xen-devel@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH v3 5/6] ioreq-server: add support for
> multiple servers
> On Mon, 2014-03-17 at 14:52 +0000, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Ian Campbell
> > > It's always struck me as odd to have a Xen<->DM communication channel
> > > sitting there in guest pfn space (regardless of who the nominal owner
> > > is).
> > >
> > > I don't suppose there is any way to pull these pages out of the guest
> > > pfn space while still accounting them to the guest. Or if there is it
> > > would probably be a whole other kettle of fish than this series.
> > >
> >
> > The closest analogy I can think of accounting-wise would be shadow
> > pages. I'll have a look at how they are handled.
> I think the big difference is that noone outside Xen needs to be able to
> refer to a shadow page, whereas the device models need some sort of
> handle onto the ring to be able to map them etc. Not insurmountable I
> suppose.

Probably not, but it's looking like it will be a bit of a can of worms. Are you 
ok with sticking to base+range HVM params for secondary emulators that can 
potentially be moved on migration for now? I.e. the save image just contains a 
count. There's still some growth room in the existing area (all pages from 
FE800000 to FF000000 AFACT) so as long as - as George said - we don't bake the 
PFN layout in, I donât think we preclude moving the emulator PFNs around in 

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