RE: [Xen-devel] GPLPV memory ballooning and x32

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 25.05.10 at 09:18, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:
> On a similar subject, is it now possible to start a hvm domain in a 
> 'ballooned down' state (via PoD perhaps) and then have PV drivers detect the 
> 'unpopulated' pages and turn them into ballooned pages?

Yes, that's (afaik) the sole purpose of PoD. And having a functional
balloon driver in the guest is a requirement then.
 
> For that to work, I would need to be able to do the following:
> . detect the unpopulated PoD pages via some hypercall(s)

See linux-2.6.18's c/s 989 and 1011. I'd be curious if you can come
up with a better mechanism. Unfortunately XENMEM_get_pod_target
can (so far) only be called from Dom0, otherwise that might be
helpful too.

> . allocate specific pages in Windows (MmAllocatePagesForMdl has Low and High 
> address parameters which suggest this sort of ability...)
> . make sure Windows doesn't touch those pages when I allocate them (I guess 
> it doesn't anyway but I can't look at the source to check...)
> . change the pages from PoD to 'empty' via some hypercall(s) - or maybe this 
> isn't necessary... I can just allocate them to balloon down, and then 'touch' 
> each page (to make xen populate it) then free them, as long as I remember 
> which pages are PoD and which are 'empty'

Jan


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