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Re: [Qemu-devel] [PATCH 6/8] memory: Sanity check that no listeners rema
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] [PATCH 6/8] memory: Sanity check that no listeners remain on a destroyed AddressSpace |
Date: |
Mon, 13 May 2013 22:57:48 +1000 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, May 13, 2013 at 02:19:50PM +0200, Paolo Bonzini wrote:
> Il 13/05/2013 14:07, Peter Maydell ha scritto:
> > 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?
>
> Yes, that could be an idea.
Fine by me, that would also naturally lead to making the listener list
per-AS. Either way, it doesn't alter the fact that pointer references
to the AS need to be removed before the AS is destroyed.
--
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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- [Qemu-devel] [PATCH 1/8] iommu: Fix compile error in ioapic.c, (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