Re: [Qemu-devel] New Memory API Question

[Avi Kivity <avi@redhat.com>]

On 10/26/2011 03:52 PM, John Baboval wrote:
> Sorry for coming late to the party on this... I only read qemu-devel
> through a filter so I missed all the discussions on the new memory
> API. I have a question as to how it works and how it's supposed to
> work in certain scenarios.
>
> It's a question of flow. I'm following the code path through the
> creation of a new memory subregion. If I'm reading this properly, it
> would seem that a MemoryRegion - for example the ones used by VGA - go
> through the following flow:
>
> memory_region_init_ram()   - (mr->destructor is set to
> memory_region_destructor_ram)
> memory_region_add_subregion(system_memory, ...) ->
>    memory_region_update_topology() ->
>       address_space_update_topology()
>          address_space_update_topology_part()
>             as_memory_range_add()   - through the ops vector
>                memory_region_prepare_ram_addr()
>
>
> At this point it seems that the destructor is overwritten with the
> memory_region_destructor_iomem(), and it loses track of the proper way
> to ever free the memory region. Is this correct, or am I missing
> something?

It's correct; this is a bug.

>
> Or does it not matter because nobody ever calls memory_region_destroy
> for system memory regions?

It can still happen via hotunplug of an ivshmem device, or memory
hotunplug (when it is eventually implemented).

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.