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Diffstat (limited to 'docs/devel/memory.rst')
| -rw-r--r-- | docs/devel/memory.rst | 24 |
1 files changed, 11 insertions, 13 deletions
diff --git a/docs/devel/memory.rst b/docs/devel/memory.rst index 57fb2ae..f22146e 100644 --- a/docs/devel/memory.rst +++ b/docs/devel/memory.rst @@ -158,21 +158,21 @@ ioeventfd) can be changed during the region lifecycle. They take effect as soon as the region is made visible. This can be immediately, later, or never. -Destruction of a memory region happens automatically when the owner -object dies. +Destruction of a memory region happens automatically when the owner object +dies. When there are multiple memory regions under the same owner object, +the memory API will guarantee all memory regions will be properly detached +and finalized one by one. The order in which memory regions will be +finalized is not guaranteed. If however the memory region is part of a dynamically allocated data -structure, you should call object_unparent() to destroy the memory region -before the data structure is freed. For an example see VFIOMSIXInfo -and VFIOQuirk in hw/vfio/pci.c. +structure, you should free the memory region in the instance_finalize +callback. For an example see VFIOMSIXInfo and VFIOQuirk in +hw/vfio/pci.c. You must not destroy a memory region as long as it may be in use by a device or CPU. In order to do this, as a general rule do not create or -destroy memory regions dynamically during a device's lifetime, and only -call object_unparent() in the memory region owner's instance_finalize -callback. The dynamically allocated data structure that contains the -memory region then should obviously be freed in the instance_finalize -callback as well. +destroy memory regions dynamically during a device's lifetime, and never +call object_unparent(). If you break this rule, the following situation can happen: @@ -198,9 +198,7 @@ this exception is rarely necessary, and therefore it is discouraged, but nevertheless it is used in a few places. For regions that "have no owner" (NULL is passed at creation time), the -machine object is actually used as the owner. Since instance_finalize is -never called for the machine object, you must never call object_unparent -on regions that have no owner, unless they are aliases or containers. +machine object is actually used as the owner. Overlapping regions and priority |