numa: call ->ram_block_removed() in ram_block_notifer_remove()

numa: call ->ram_block_removed() in ram_block_notifer_remove()

When a RAMBlockNotifier is added, ->ram_block_added() is called with all
existing RAMBlocks. There is no equivalent ->ram_block_removed() call
when a RAMBlockNotifier is removed.

The util/vfio-helpers.c code (the sole user of RAMBlockNotifier) is fine
with this asymmetry because it does not rely on RAMBlockNotifier for
cleanup. It walks its internal list of DMA mappings and unmaps them by
itself.

Future users of RAMBlockNotifier may not have an internal data structure
that records added RAMBlocks so they will need ->ram_block_removed()
callbacks.

This patch makes ram_block_notifier_remove() symmetric with respect to
callbacks. Now util/vfio-helpers.c needs to unmap remaining DMA mappings
after ram_block_notifier_remove() has been called. This is necessary
since users like block/nvme.c may create additional DMA mappings that do
not originate from the RAMBlockNotifier.

Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20221013185908.1297568-4-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>