Re: Sharing a page of memory between the guest and host

[Cam Macdonell <cam@cs.ualberta.ca>]

Anthony Liguori wrote:
> Cam Macdonell wrote:
>> Hello,
>>
>> Is it possible to share a memory (a page perhaps) between the host and 
>> guest?
> 
> Yes, the host always has access to all of the guests memory.  All of the 
> virtio drivers depend on this fact.  With KVM, the userspace (in this 
> case, QEMU), just tells the kernel about a virtual address region and 
> the kernel uses that region of virtual memory for the guest's physical 
> memory.  Whatever you (as userspace) maps into that region is totally up 
> to you.
> 
>>   More precisely, could a host and guest share a memory-mapped file?
> 
> It will be a lot easier once we have MMU notifiers upstream.  You'll be 
> able to simply mmap(MAP_FIXED) a file into the guest's physical address 
> space even while it's running.  For now, you have to setup these 
> mappings before the VM starts.
> 
>>   If one were crazy enough to want to do this, where should they look 
>> first?
>>   
> 
> If you look at the -mem-file implementation in the latest git, you'll 
> see that all the guest's memory can be an mmap()'d file.

Hi Anthony,

In setting up the guest memory to share a page, I need to make the 
kernel aware of that page.  Is the best way to do this through a little 
virtio-like PCI device or is there an easier to get dynamic info into 
the guest kernel?

Also, is the mem-file implementation in a specific branch of the latest 
GIT or is it within the main branch somewhere, I've been unable to find it?

Thanks a bunch,
Cam

-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/