[Xen-devel] RE: touching a missing page causes DomU to die

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

> 
> James,
> 
>   Then I guess I don't understand why the double buffering code is
attempting
> to use the memory you have allocated and handed back to Xen. If your
code
> allocated it then nothing else should be trying to use it, right?
> 

It's during hibernation. Windows writes out all memory to disk and turns
the power off. It can be read back in when the power comes back on,
restoring the system back to its previous state.

I'm not sure why you'd use hibernate when xm save exist, but some users
want it, and there should be a way to make it work. I think I've solved
it now by allocating memory for the grant table out of real memory space
instead of mmio space, and giving those pages back to xen before putting
the grant table pages there. I'll need another solution if I ever want
to support PoD though.

James

>   Paul
> 
> > -----Original Message-----
> > From: James Harper [mailto:james.harper@xxxxxxxxxxxxxxxx]
> > Sent: 21 January 2011 21:52
> > To: Paul Durrant; xen-devel@xxxxxxxxxxxxxxxxxxx
> > Subject: RE: touching a missing page causes DomU to die
> >
> > > >
> > > > My Windows PV drivers are crashing during hibernation, and I've
> > > > finally
> > > > figured out that it's because the windows hibernation mode
> > driver
> > > > double
> > > > buffers memory before handing it to my block device driver, and
> > in
> > > > doing
> > > > so 'touches' some pages of memory I have given back to xen (to
> > work
> > > > around a domu save crash).
> > > >
> > >
> > > You've given memory belonging to the crash kernel back to Xen?
> > >
> >
> > My driver allocates a few pages of memory and calls decrease
> > reservation
> > to give them back to xen. This is to work around a problem saving
> > (or
> > restoring?) a domu under xen where I need to give back an amount of
> > pages equal to the pages xen has given me for setup (grant table I
> > think).
> >
> > James

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