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

[Alexey Kardashevskiy]

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