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

[David Gibson]

On Tue, May 26, 2015 at 10:58:02AM +0200, 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?
> 
> > 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.
> 
> > 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...

Ah, yeah, drat.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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