RE: [Xen-devel] PoD in other (not GPLPV) drivers

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> I actually have plans to push it earlier because we balloon down quite
late at
> the moment (off the back of the START IRP in the top level bus
driver). We are
> reliant upon zero-page sweeping code in Xen to save us from guest
crashing up
> to that point.
> 

I've modified GPLPV to balloon down at DriverEntry time, which seems to
be early enough. Prior to that, memory=128 and maxmem=1024 was enough to
cause a crash under 2008, basically as soon as I tried to access the
registry in DriverEntry. My drivers are using WDF and are therefore
loading after the KMDF framework which is going to use additional
resources. My backup plan is to write a WDM driver that loads even
earlier than that and does the allocation, passing it to the real PV
drivers later on, although my concern there is that Windows may not like
memory allocated by one driver being freed by another...

I've never heard of 'zero-page sweeping code' before... is that a way of
xen reallocating a previously touched page if it contains all 0's if we
want a page beyond our allocation limit? That might explain why my
initial balloon down is so slow! I can tell windows to not zero pages
before it gives them to me when I do the initial balloon down... what
are your thoughts on that? Although it's unlikely at boot time, in
theory they could contain sensitive information and I'm supposed to zero
them before handing them back to xen according to the docs.

James


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