Re: [Qemu-devel] [PATCH 06/15] memory: use refcnt to manage MemoryRegion

[Avi Kivity]

On 08/10/2012 09:44 AM, liu ping fan wrote:
>>> In the previous discussion, you have suggest add dev->ref++ in
>>> core_region_add.  But I think, if we can move it to higher layer --
>>> memory_region_{add,del}_subregion, so we can avoid to duplicate do
>>> this in other xx_region_add.
>>
>> Why would other memory listeners be impacted?  They all operate under
>> the big qemu lock.  If they start using devices outside the lock, then
>> they need to take a reference.
>>
> Yes, if unplug path in the protection of big lock.
> And just one extra question, for ram-unplug scene, how do we protect from:
>   updater:  ram-unplug -->qemu free() --> brk() invalidate this vaddr interval
>   reader:  vhost-thread copy data from the interval
> I guess something like lock/ref used by them, but can not find such
> mechanism in vhost_set_memory() to protect the scene against
> vhost_worker()

VHOST_SET_MEM_TABLE uses synchronize_srcu() to ensure no readers are
active before returning.


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