Re: [Qemu-devel] [PATCH] Fix off-by-1 error in RAM migration code

[David Gibson <dwg@au1.ibm.com>]

On Wed, Oct 31, 2012 at 01:08:16PM +0200, Orit Wasserman wrote:
> On 10/31/2012 05:43 AM, David Gibson wrote:
> > The code for migrating (or savevm-ing) memory pages starts off by creating
> > a dirty bitmap and filling it with 1s.  Except, actually, because bit
> > addresses are 0-based it fills every bit except bit 0 with 1s and puts an
> > extra 1 beyond the end of the bitmap, potentially corrupting unrelated
> > memory.  Oops.  This patch fixes it.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  arch_init.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch_init.c b/arch_init.c
> > index e6effe8..b75a4c5 100644
> > --- a/arch_init.c
> > +++ b/arch_init.c
> > @@ -568,7 +568,7 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
> >      int64_t ram_pages = last_ram_offset() >> TARGET_PAGE_BITS;
> >  
> >      migration_bitmap = bitmap_new(ram_pages);
> > -    bitmap_set(migration_bitmap, 1, ram_pages);
> > +    bitmap_set(migration_bitmap, 0, ram_pages);
> >      migration_dirty_pages = ram_pages;
> >  
> >      bytes_transferred = 0;
> > 
> You are correct, good catch.
> Reviewed-by: Orit Wasserman <owasserm@redhat.com>

Juan,

Sorry, forgot to CC you on the original mailing here, which I should
have done.  This is a serious bug in the migration code and we should
apply to mainline ASAP.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson