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Re: [Qemu-devel] [PATCH 6/8] memory: Sanity check that no listeners rema
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH 6/8] memory: Sanity check that no listeners remain on a destroyed AddressSpace |
Date: |
Mon, 13 May 2013 13:07:20 +0100 |
On 13 May 2013 12:48, David Gibson <address@hidden> wrote:
> On Mon, May 13, 2013 at 12:10:10PM +0100, Peter Maydell wrote:
>> Hmm, is this the ideal semantics? Typically the owner of the
>> MemoryListener isn't the owner of the AddressSpace so it isn't
>> necessarily in a position to guarantee that it can unregister
>> the listener before the address space is destroyed. In fact
>> as the listener API is currently documented, the filter
>> argument is just an optimisation to save the callbacks having
>> to filter out irrelevant information themselves.
>
> If so, then it's broken by design. There's no guarantee that after an
> AddressSpace is destroyed another one won't be created at the same
> address (in fact, depending on your malloc() implementation, it could
> be very likely). So references by pointer to an object *must* be
> removed before the object itself is freed.
Mmm. Looking through the code it turns out we don't actually
make use of the ability to pass NULL as a filter (except in
target-arm/kvm.c which was just me being lazy and not passing
in the system address space). Perhaps we should just drop that
capability, at which point you have a clearer "you are listening
on one AS and you must make sure you arrange to unregister before
that AS goes away" API definition?
-- PMM
- [Qemu-devel] [PATCH 4/8] pci: Use AddressSpace rather than MemoryRegion to represent PCI DMA space, (continued)
[Qemu-devel] [PATCH 5/8] pci: Introduce helper to retrieve a PCI device's DMA address space, David Gibson, 2013/05/13
[Qemu-devel] [PATCH 8/8] vfio: Create VFIOAddressSpace objects as needed, David Gibson, 2013/05/13
[Qemu-devel] [PATCH 3/8] pci: Rework PCI iommu lifetime assumptions, David Gibson, 2013/05/13
Re: [Qemu-devel] [0/8] RFC: VFIO and guest side IOMMUs, revisited, Paolo Bonzini, 2013/05/13