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RE: [Xen-users] Inter-VM Shared memory with HVM DomUs

Todd: Thanks for responding and getting Dan's attention on this. I appreciate 
your help.

Dan: Your guess was correct. Tmem, although very useful, isn't what I am 
looking for at the moment. I do hope to use it for another application that I 
have in mind though in the near future. For now I am more interested in using 
the grant table mechanism to enable memory sharing between VMs.

After thinking about my problem some more, I believe what is happening in that 
the HVM devices are being auto-unplugged somehow by my guest kernel, once it 
detects the corresponding PV drivers. However, the PV drivers are not working 
(perhaps something else is needed to really turn them on) and this puts my 
system into a state where no virtual disk is present. I will looking into a way 
to prevent my HVM devices from getting removed. Hopefully that will fix the 


-----Original Message-----
From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx] 
Sent: Tuesday, August 30, 2011 7:15 AM
To: Todd Deshane; Anil Rao
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] Inter-VM Shared memory with HVM DomUs

> From: Todd Deshane [mailto:todd.deshane@xxxxxxx]
> Sent: Monday, August 29, 2011 7:17 PM
> To: Anil Rao
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx; Dan Magenheimer
> Subject: Re: [Xen-users] Inter-VM Shared memory with HVM DomUs
> On Mon, Aug 29, 2011 at 7:59 PM, Anil Rao <anil.rao@xxxxxxxxxxxx> wrote:
> > Hello,
> >
> > I am interested in having a bunch of HVM DomUs share a memory 
> > segment that is exported by Dom0. I am currently on a Xen 4.1.0 
> > system with the Jeremy PV-OPTs Dom0. For my initial test, my DomU 
> > kernel is running a 32-bit PAE kernel based on Fedora 15. I 
> > configured the PV options to turn on the Xen Platform Drivers 
> > (configured as modules). When I start the DomU, it cannot find the root and 
> > swap partitions and then falls into a debug shell.
> >
> > The Standard Fedora 15 32-bit kernel (with no PV options configured) 
> > works fine as a HVM DomU on my host. Is there a special recipe that 
> > I must follow to get PV-on-HVM working? From reading various posts 
> > it appears that PV-on-HVM is required in order to get inter-VM 
> > shared memory to work with HVM DomUs. Any thoughts/suggestions would be 
> > most appreciated.
> >
> Take a look here:
> http://oss.oracle.com/projects/tmem/
> I've also added Dan to the CC he may have some insights.
> As he has submitted tmem patches for upstream Linux:
> http://xen.markmail.org/search/?q=tmem#query:tmem%20from%3A%22Dan%20Ma
> genheimer%22%20date%3A201107%20+ 
> page:1+mid:jvln4hk5agf5onzz+state:results

Anil, as you may have noticed from the above link, Transcendent Memory ("tmem") 
is really for sharing memory _capacity_ between guests not the actual data in 
memory.  So I am guessing tmem will not be useful to you, but if I am wrong, 
please let me know.

Todd, thanks anyway!


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