Re: WARNING: at /usr/src/modules/kvm/mmu.c:390 account_shadowed()

Thomas Cataldo
2008-04-30T19:34:08Z

On Sat, Apr 26, 2008 at 10:08 AM, Avi Kivity <avi@qumranet.com> wrote:
> Marcelo Tosatti wrote:
>
> > On Wed, Apr 23, 2008 at 09:30:06AM +0300, Avi Kivity wrote:
> >
> >
> > >
> > > > as I got no reply, I guess it is a bad setup on my part. If that might
> > > > help, this happenned while I was doing a "make -j" on webkit svn tree
> > > > (ie. heavy c++ compilation workload) .
> > > >
> > > >
> > > >
> > > No this is not bad setup. No amount of bad setup should give this
> warning.
> > >
> > > You didn't get a reply because no one knows what to make of it, and
> because it's much more fun to debate endianess or contemplete guests with
> eighty thousand disks than to fix those impossible bugs. If you can give
> clear instructions on how to reproduce this, we will try it out. Please be
> sure to state OS name and versions for the guest as well as the host.
> > >
> > >
> >
> > It is valid to have more than PAGES_PER_HPAGE in the largepage's
> > shadowed count. If the gpte read races with a pte-update-from-guest (and
> > the pte update results in a different sp->role), it might account twice
> > for a single gfn.
> >
> > Such "zombie" shadow pages should eventually be removed through
> > recycling, allowing for instantiation of a large page, unless references
> > can be leaked. Can't spot such leakage problem though.
> >
> >
> >
>
> That strikes me as unlikely (though a valid scenario).
>
> An alternative explanation is that we're seeing a nonpae guest, so each
> page can be shadowed in two different roles (two quadrants for a pte page)
> or even four (for a pgd page).
>
> Thomas, are you running a 32-bit nonpae guest?
>

Yes it was 32bit nonpae guest on 32bit nonpae host.

Severals things :
- I never reproduiced the problem
- The problem happened under heavy load, and I was experiencing
slowdown on this laptop after a few hours of work. For example my
system was reporting 4500fps on glxgears after fresh boot, and 500fps
after a day of work. After some investigations, I found on the dell
website that my laptop had fans activation problems with my bios
version. After bios upgrade, my system does slows after heavy load. So
as my system was heating to much because of this bios problem, I think
you can forget my report.