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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 23:42:27 +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 11:31 PM, Paolo Bonzini wrote:

On 26/05/2015 15:28, Alexey Kardashevskiy wrote:

My initial concern was if I can or cannot do:

memory_region_init_iommu + memory_region_add_subregion
memory_region_del_subregion + object_unref

outside of init/realize/unrealize/finalize.

You said I cannot do unparenting but as I am not doing this (and I just
do unref()) - I am fine. That's what I meant.

Well, if you do the above you have two different bugs:

1) you leak the original child property

2) you initialize the second region on top of the first, so you have two
regions pointing to the same memory

The next patch of this patchset changes:
        memory_region_add_subregion(&root, &iommu)

        memory_region_del_subregion(&root, &iommu)

These spapr_tce_xxx are called by request from the guest. &root is a container and exists as long as sPAPRTCETable exists.

Where do I get a leaking child property here?

This is even worse than unparenting :) and would have been wrong even
without the RCU changes.

I believe you :) But do not understand :)


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