[Qemu-devel] [PATCH v2 1/2] memory: Inherit has_coalesced_range from the same old FlatRange

[Peter Xu <peterx@redhat.com>]

The previous has_coalesced_range counter has a problem in that it only
works for additions of coalesced mmio ranges but not deletions.  The
reason is that has_coalesced_range information can be lost when the
FlatView updates the topology again when the updated region is not
covering the coalesced regions. When that happens, due to
flatrange_equal() is not checking against has_coalesced_range, the new
FlatRange will be seen as the same one as the old and the new
instance (whose has_coalesced_range will be zero) will replace the old
instance (whose has_coalesced_range _could_ be non-zero).

To fix it, we inherit the has_coalesced_range value from the old
FlatRange to the new one if it's describing the identical range when
updating the topology.

Without this patch, MemoryListener.coalesced_io_del is hardly being
called due to has_coalesced_range will be mostly zero in
flat_range_coalesced_io_del() when topologies frequently change for
the "memory" address space.

Fixes: 3ac7d43a6fbb5d4a3
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 memory.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/memory.c b/memory.c
index 8141486832..c53dcfc092 100644
--- a/memory.c
+++ b/memory.c
@@ -939,6 +939,15 @@ static void address_space_update_topology_pass(AddressSpace *as,
             /* In both and unchanged (except logging may have changed) */
 
             if (adding) {
+                /*
+                 * We must inherit the has_coalesced_range information
+                 * if the new FlatRange is exactly the same as the old
+                 * one, because it'll be used to conditionally call
+                 * the coalesced mmio deletion listeners correctly in
+                 * flat_range_coalesced_io_del() when the FlatRange
+                 * needs to really go away.
+                 */
+                frnew->has_coalesced_range = frold->has_coalesced_range;
                 MEMORY_LISTENER_UPDATE_REGION(frnew, as, Forward, region_nop);
                 if (frnew->dirty_log_mask & ~frold->dirty_log_mask) {
                     MEMORY_LISTENER_UPDATE_REGION(frnew, as, Forward, log_start,
-- 
2.21.0