On 28/06/2017 09:30, Juan Quintela wrote:
> Haozhong Zhang <haozhong.zh...@intel.com> 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 <stefa...@redhat.com>
>> Signed-off-by: Haozhong Zhang <haozhong.zh...@intel.com>
>
> Reviewed-by: Juan Quintela <quint...@redhat.com>
>
> As this function is only used on migration, should I integrate it on my
> next push, or do you want to pull it, Paolo?
>
> Later, Juan.
>
>
>> ---
>> include/exec/ram_addr.h | 8 +++++---
>> 1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
>> index 73d1bea8b6..cbc797ed05 100644
>> --- a/include/exec/ram_addr.h
>> +++ b/include/exec/ram_addr.h
>> @@ -377,6 +377,7 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock
>> *rb,
>> uint64_t *real_dirty_pages)
>> {
>> ram_addr_t addr;
>> + ram_addr_t offset = rb->offset;
>> unsigned long page = BIT_WORD(start >> TARGET_PAGE_BITS);
>> uint64_t num_dirty = 0;
>> unsigned long *dest = rb->bmap;
>> @@ -386,8 +387,9 @@ 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 + 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);
The shadowing between the two variables named offset is a bit ugly.
Please use rb->offset in the initialization of "word", and declare...
>>
>> rcu_read_lock();
>> @@ -416,7 +418,7 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock
>> *rb,
>> } else {
... "ram_addr_t offset = offset" here.
Paolo
>> 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;
