Re: [PATCH] xen/p2m/m2p/gnttab: do not add failed grant maps to m2p override

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Mar 04, 2011 at 05:47:08PM +0000, Ian Campbell wrote:
> On Fri, 2011-03-04 at 17:38 +0000, Ian Campbell wrote:
> > The caller will not undo a mapping which failed and therefore the
> > override will not be removed.
> > 
> > This is especially bad in the case of GNTMAP_contains_pte mapping type
> > mappings where m2p_add_override will destroy the kernel mapping of the
> > page.
> > 
> > This was observed via a failure of map_grant_pages in gntdev_mmap (due
> > to userspace using a bad grant reference), which left the page in
> > question unmapped (because it was a GNTMAP_contains_pte mapping) which
> > led to a crash later on.
> 
> My original motivation for looking into this was a dom0 kernel crash in
> gntdev exposed by using the qemu disk backend on 2.6.32 (by mistake due
> to not loading blktap). The crash was in mn_release but was root caused
> by a map_grant_pages() failing (due to a bogus grant ref).
> 
> It seems that Daniel's "xen-gntdev: Add reference counting to maps" +

This one:
http://article.gmane.org/gmane.comp.emulators.xen.devel/100076 ?

> "xen/p2m/m2p/gnttab: do not add failed grant maps to m2p override" +
> this fix are sufficient to fix it for 2.6.38-rc7+ but I wonder if we

Can you point me to the "this fix" ? You mention three patches but
the last one is the same as 
"xen/p2m/m2p/gnttab: do not add failed grant maps to m2p override"

so that looks to be two patches.

> also want it fixed for 2.6.32? I think in that case backporting Daniel's
> patches is the best bet. (this fix won't be necessary, no m2p overlay in
> 2.6.32).
> 
> Ian.
> 
> > 
> > Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > Cc: Daniel De Graaf <dgdegra@tycho.nsa.gov>
> > Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
> > ---
> >  drivers/xen/grant-table.c |    4 ++++
> >  1 files changed, 4 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> > index 1a9bc2b..d0e30ce 100644
> > --- a/drivers/xen/grant-table.c
> > +++ b/drivers/xen/grant-table.c
> > @@ -462,6 +462,10 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> >  		return ret;
> >  
> >  	for (i = 0; i < count; i++) {
> > +		/* Do not add to override if the map failed. */
> > +		if (map_ops[i].status)
> > +			continue;
> > +
> >  		if (map_ops[i].flags & GNTMAP_contains_pte) {
> >  			pte = (pte_t *) (mfn_to_virt(PFN_DOWN(map_ops[i].host_addr)) +
> >  				(map_ops[i].host_addr & ~PAGE_MASK));
>