Re: [Qemu-devel] [PATCH v2] exec: fix access to ram_list.dirty_memory when sync dirty bitmap

[Juan Quintela]

Paolo Bonzini <address@hidden> wrote:
> On 28/06/2017 10:37, Haozhong Zhang wrote:
>> In cpu_physical_memory_sync_dirty_bitmap(rb, start, ...), the 2nd
>> argument 'start' is relative to the start of the ramblock 'rb'. When
>> it's used to access the dirty memory bitmap of ram_list (i.e.
>> ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION]->blocks[]), an offset to
>> the start of all RAM (i.e. rb->offset) should be added to it, which has
>> however been missed since c/s 6b6712efcc. For a ramblock of host memory
>> backend whose offset is not zero, cpu_physical_memory_sync_dirty_bitmap()
>> synchronizes the incorrect part of the dirty memory bitmap of ram_list
>> to the per ramblock dirty bitmap. As a result, a guest with host
>> memory backend may crash after migration.
>> 
>> Fix it by adding the offset of ramblock when accessing the dirty memory
>> bitmap of ram_list in cpu_physical_memory_sync_dirty_bitmap().
>> 
>> Reported-by: Stefan Hajnoczi <address@hidden>
>> Signed-off-by: Haozhong Zhang <address@hidden>
>> ---
>> Changes in v2:
>>  * Avoid shadowing variable 'offset'. (Paolo)
>> ---
>>  include/exec/ram_addr.h | 9 ++++++---
>>  1 file changed, 6 insertions(+), 3 deletions(-)
>> 
>> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
>> index 73d1bea8b6..c04f4f67f6 100644
>> --- a/include/exec/ram_addr.h
>> +++ b/include/exec/ram_addr.h
>> @@ -386,8 +386,9 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock 
>> *rb,
>>          int k;
>>          int nr = BITS_TO_LONGS(length >> TARGET_PAGE_BITS);
>>          unsigned long * const *src;
>> -        unsigned long idx = (page * BITS_PER_LONG) / 
>> DIRTY_MEMORY_BLOCK_SIZE;
>> -        unsigned long offset = BIT_WORD((page * BITS_PER_LONG) %
>> +        unsigned long word = BIT_WORD((start + rb->offset) >> 
>> TARGET_PAGE_BITS);
>> +        unsigned long idx = (word * BITS_PER_LONG) / 
>> DIRTY_MEMORY_BLOCK_SIZE;
>> +        unsigned long offset = BIT_WORD((word * BITS_PER_LONG) %
>>                                          DIRTY_MEMORY_BLOCK_SIZE);
>>  
>>          rcu_read_lock();
>> @@ -414,9 +415,11 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock 
>> *rb,
>>  
>>          rcu_read_unlock();
>>      } else {
>> +        ram_addr_t offset = rb->offset;
>> +
>>          for (addr = 0; addr < length; addr += TARGET_PAGE_SIZE) {
>>              if (cpu_physical_memory_test_and_clear_dirty(
>> -                        start + addr,
>> +                        start + addr + offset,
>>                          TARGET_PAGE_SIZE,
>>                          DIRTY_MEMORY_MIGRATION)) {
>>                  *real_dirty_pages += 1;
>> 
>
> Acked-by: Paolo Bonzini <address@hidden>
>
> Juan, please take care of this yourself!  Thanks,

Already sent in a pull request 5 mins ago.
(so, it don't have your Ack :-)

Thanks, Juan.