Re: [Qemu-devel] [PATCH 2/2] migration: extend migration_bitmap

[Juan Quintela]

Li Zhijian <address@hidden> wrote:
> Prevously, if we hotplug a device(e.g. device_add e1000) during
> migration is processing in source side, qemu will add a new ram
> block but migration_bitmap is not extended.
> In this case, migration_bitmap will overflow and lead qemu abort
> unexpectedly.
>
> Signed-off-by: Li Zhijian <address@hidden>
> Signed-off-by: Wen Congyang <address@hidden> 

Just curious, how are you testing this?
because you need a way of doing the hot-plug "kind of" atomically on
both source and destination, no?


> ---
>  exec.c                  |  7 ++++++-
>  include/exec/exec-all.h |  1 +
>  migration/ram.c         | 16 ++++++++++++++++
>  3 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/exec.c b/exec.c
> index f7883d2..04d5c05 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1401,6 +1401,11 @@ static ram_addr_t ram_block_add(RAMBlock *new_block, 
> Error **errp)
>          }
>      }
>  
> +    new_ram_size = MAX(old_ram_size,
> +              (new_block->offset + new_block->max_length) >> 
> TARGET_PAGE_BITS);
> +    if (new_ram_size > old_ram_size) {
> +        migration_bitmap_extend(old_ram_size, new_ram_size);
> +    }
>      /* Keep the list sorted from biggest to smallest block.  Unlike QTAILQ,
>       * QLIST (which has an RCU-friendly variant) does not have insertion at
>       * tail, so save the last element in last_block.
> @@ -1435,7 +1440,7 @@ static ram_addr_t ram_block_add(RAMBlock *new_block, 
> Error **errp)
>              ram_list.dirty_memory[i] =
>                  bitmap_zero_extend(ram_list.dirty_memory[i],
>                                     old_ram_size, new_ram_size);
> -       }
> +        }

Whitespace noise

>      }
>      cpu_physical_memory_set_dirty_range(new_block->offset,
>                                          new_block->used_length,
> diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
> index 2573e8c..dd9be44 100644
> --- a/include/exec/exec-all.h
> +++ b/include/exec/exec-all.h
> @@ -385,4 +385,5 @@ static inline bool cpu_can_do_io(CPUState *cpu)
>      return cpu->can_do_io != 0;
>  }
>  
> +void migration_bitmap_extend(ram_addr_t old, ram_addr_t new);
>  #endif
> diff --git a/migration/ram.c b/migration/ram.c
> index 4754aa9..70dd8da 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1063,6 +1063,22 @@ static void reset_ram_globals(void)
>  
>  #define MAX_WAIT 50 /* ms, half buffered_file limit */
>  
> +void migration_bitmap_extend(ram_addr_t old, ram_addr_t new)
> +{
> +    qemu_mutex_lock(&migration_bitmap_mutex);
> +    if (migration_bitmap) {
> +        unsigned long *old_bitmap = migration_bitmap, *bitmap;
> +        bitmap = bitmap_new(new);
> +        bitmap_set(bitmap, old, new - old);
> +        memcpy(bitmap, old_bitmap,
> +               BITS_TO_LONGS(old) * sizeof(unsigned long));

Shouldn't the last two sentences be reversed? memcpy could "potentially"
overwrote part of the bits setted on bitmap_set.  (notice the
potentially part, my guess is that we never get a bitmap that is not
word aligned, but well ....)

My understanding of the rest look right.

Later, Juan.