Re: [Xen-devel] [PATCH] xen/balloon: set ballooned out pages as invalid in p2m

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 1 Jul 2014, Konrad Rzeszutek Wilk wrote:
> On Tue, Jul 01, 2014 at 03:00:16PM +0100, David Vrabel wrote:
> > On 01/07/14 14:58, Konrad Rzeszutek Wilk wrote:
> > > On Tue, Jul 01, 2014 at 02:37:48PM +0100, David Vrabel wrote:
> > >> Since cd9151e26d31048b2b5e00fd02e110e07d2200c9 (xen/balloon: set a
> > >> mapping for ballooned out pages), a ballooned out page had its entry
> > >> in the p2m set to the MFN of one of the scratch pages.  This means
> > >> that the p2m will contain many entries pointing to the same MFN.
> > >>
> > >> During a domain save, these many-to-one entries are not identified as
> > >> such and the scratch page is saved multiple times. On restore the
> > >> ballooned pages are populated with new frames and the domain may use
> > >> up its allocation before all pages can be restored.
> > >>
> > >> Set ballooned out pages as INVALID_P2M_ENTRY in the p2m (as they were
> > >> before), preventing them from being saved and re-populated on restore.
> > >>
> > > 
> > > Won't that invalide the primal purpose of the scratch page code?
> > > 
> > > That is  cd9151e26d31048b2b5e00fd02e110e07d2200c9
> > > 
> > >     xen/balloon: set a mapping for ballooned out pages
> > > " Allocate a page per cpu and map all the ballooned out pages to the
> > >     corresponding mfn. Set the p2m accordingly. This way reading from a
> > >     ballooned out page won't cause a kernel crash (see
> > >     http://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html).
> > > "
> > > ?
> > 
> > No, because we still have a virtual mapping for the ballooned out page.
> 
> If you could add that comment in that would reflect that - IMHO
> it would be good.

Agreed.
Aside from that:

Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel