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

From: Alexey Kardashevskiy
Subject: Re: [Qemu-devel] [PATCH qemu v7 06/14] spapr_iommu: Introduce "enabled" state for TCE table
Date: Tue, 26 May 2015 20:15:23 +1000
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 05/26/2015 06:58 PM, Paolo Bonzini wrote:
Hash: SHA256

On 26/05/2015 04:46, David Gibson wrote:
On Tue, May 26, 2015 at 01:05:56AM +1000, Alexey Kardashevskiy
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...


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