Re: [Qemu-devel] [PATCH qemu v7 06/14] spapr_iommu: Introduce "enabled" state for TCE table

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 05/26/2015 06:58 PM, Paolo Bonzini wrote:
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> On 26/05/2015 04:46, David Gibson wrote:
>> On Tue, May 26, 2015 at 01:05:56AM +1000, Alexey Kardashevskiy
>> wrote:
>>> Hi Paolo,
>>>
>>> I have had a conversation with Mike and it turns out I am not
>>> allowed to create/remove memory regions dynamically
>>> (docs/memory.txt:101); otherwise "destroying regions during
>>> reset causes assertion in RCU thread during PHB/IOMMU
>>> unplug/unparent". Is it because patch just missing some
>>> unref()/unparent() call or it is totally wrong and I have to
>>> implement subregions (on a PCI bus address space) myself if I
>>> want dynamic DMA windows? Thanks!
>
> I'm blind, can you explain the path where that happens?


There was a "[RFC PATCH 00/15] spapr: add support for PHB hotplug" patchset 
from Mike, this patch added "unrealize" for spapr_phb:

[RFC PATCH 05/15] spapr_pci: add PHB unrealize

I believe I am dealing with the fixed version of this patch so I'll ask 
Mike to respin it.


>
>> So, the sentences after that one note an exception for alias and
>> container regions.  I think iommu regions should behave similarly
>> - in a sense they're just a procedurally generated collection of
>> alias regions.
>
> The difference is that containers and aliases are resolved at the time
> the memory region tree is flattened, while IOMMU regions are resolved
> at run time.


So they are not parts of flattened view and I should be able to add/remove 
these IOMMU subregions any time I like?


>> If it's not true now that they can be unparented at any time like
>> alias regions, we should probably try to make it true.
>
> Unfortunately it's not so easy...





-- 
Alexey