On Thu, Oct 02, 2025 at 03:23:10PM -0400, Peter Xu wrote:
> On Wed, Sep 17, 2025 at 07:32:48PM +0900, Akihiko Odaki wrote:
> > +static int del_memory_region(Object *child, void *opaque)
> > +{
> > + MemoryRegion *mr = (MemoryRegion *)object_dynamic_cast(child,
> > TYPE_MEMORY_REGION);
> > +
> > + if (mr && mr->container) {
> > + memory_region_del_subregion(mr->container, mr);
> > + }
> > +
> > + return 0;
> > +}
> > +
> > static void device_set_realized(Object *obj, bool value, Error **errp)
> > {
> > DeviceState *dev = DEVICE(obj);
> > @@ -582,6 +593,7 @@ static void device_set_realized(Object *obj, bool
> > value, Error **errp)
> > if (dc->unrealize) {
> > dc->unrealize(dev);
> > }
> > + object_child_foreach(OBJECT(dev), del_memory_region, NULL);
>
> PS: I'll keep throwing some pure questions here, again, Paolo - it doesn't
> need to block merging if you're confident with the general approach.
>
> Said that, a few things I still want to mention after I read this series..
>
> One thing I really feel hard to review such work is, you hardly describe
> the problems the series is resolving.
>
> For example, this patch proposed auto-detach MRs in unrealize() for qdev,
> however there's nowhere describing "what will start to work, while it
> doesn't", "how bad is the problem", etc.. All the rest patches are about
> "what we can avoid do" after this patch.
For this part, I should be more clear on what I'm requesting on the
answers.
I think I get the whole point that MRs (while still with MR refcount
piggypacked, as of current QEMU master does) can circular reference itself
if not always detached properly, so explicitly my question is about:
- What devices / use case you encountered, that QEMU has such issue?
Especially, this is about after we have merged commit ac7a892fd3 "memory:
Fix leaks due to owner-shared MRs circular references". Asking because I
believe most of them should already auto-detach when owner is shared.
- From above list of broken devices, are there any devices that are
hot-unpluggable (aka, high priority)? Is it a problem if we do not
finalize a MR if it is never removable anyway?
>
> Meanwhile, the cover letter is misleading. It is:
>
> [PATCH 00/14] Fix memory region use-after-finalization
>
> I believe it's simply wrong, because the whole series is not about
> finalize() but unrealize(). For Device class, it also includes the exit()
> which will be invoked in pci_qdev_unrealize(), but that is also part of the
> unrealize() routine, not finalize().
>
> The other question is, what if a MR has a owner that is not the device
> itself? There's no place enforcing this, hence a qdev can logically have
> some sub-objects (which may not really be qdev) that can be the owner of
> the memory regions. Then the device emulation will found that some MRs are
> auto-detached and some are not.
>
> One example that I'm aware of is this:
>
> https://lore.kernel.org/all/[email protected]/#t
>
> TYPE_VIRTIO_SHARED_MEMORY_MAPPING is an object, not qdev here, which can be
> the owner of the MR.
>
> Thanks,
>
> --
> Peter Xu
--
Peter Xu
