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

[Orit Wasserman <owasserm@redhat.com>]

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>