Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)

[Julien Grall]

Hi,

On 3/14/19 8:37 AM, Juergen Gross wrote:
> On 12/03/2019 20:46, David Hildenbrand wrote:
> > On 12.03.19 19:23, David Hildenbrand wrote:
> >
> > I guess something like this could do the trick if I understood it correctly:
> >
> > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> > index 39b229f9e256..d37dd5bb7a8f 100644
> > --- a/drivers/xen/balloon.c
> > +++ b/drivers/xen/balloon.c
> > @@ -604,6 +604,7 @@ int alloc_xenballooned_pages(int nr_pages, struct
> > page **pages)
> >          while (pgno < nr_pages) {
> >                  page = balloon_retrieve(true);
> >                  if (page) {
> > +                       __ClearPageOffline(page);
> >                          pages[pgno++] = page;
> >   #ifdef CONFIG_XEN_HAVE_PVMMU
> >                          /*
> > @@ -645,8 +646,10 @@ void free_xenballooned_pages(int nr_pages, struct
> > page **pages)
> >          mutex_lock(&balloon_mutex);
> >
> >          for (i = 0; i < nr_pages; i++) {
> > -               if (pages[i])
> > +               if (pages[i]) {
> > +                       __SetPageOffline(pages[i]);
> >                          balloon_append(pages[i]);
> > +               }
> >          }
> >
> >          balloon_stats.target_unpopulated -= nr_pages;
> >
> >
> > At least this way, the pages allocated (and thus eventually mapped to
> > user space) would not be marked, but the other ones would remain marked
> > and could be excluded by makedumptool.
>
> I think this patch should do the trick. Julien, could you give it a
> try? On x86 I can't reproduce your problem easily as dom0 is PV with
> plenty of unpopulated pages for grant memory not suffering from
> missing "offline" bit.

Sure. I managed to get the console working with the patch suggested by 
David. Feel free to add my tested-by if when you resend it as is.

Cheers,

--
Julien Grall