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

[Li Zhijian <lizhijian@cn.fujitsu.com>]

On 06/26/2015 05:05 PM, Juan Quintela wrote:
> Li Zhijian <lizhijian@cn.fujitsu.com> 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 <lizhijian@cn.fujitsu.com>
>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
> 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 ....)

reverse the last two sentences would be better.
i will fix it in next version.

Thanks
Li Zhijian

> My understanding of the rest look right.
>
> Later, Juan.
> .
>