[Qemu-devel] [PULL 4/5] memory_region_present: return false if address is not found in child MemoryRegion

["Michael S. Tsirkin" <mst@redhat.com>]

From: Igor Mammedov <imammedo@redhat.com>

Windows XP shows COM2 port as non functional in
"Device Manager" although no COM2 port backing device
is present in QEMU.

This regression is really due to
3bb28b7208b349e7a1b326e3c6ef9efac1d462bf?
    memory: Provide separate handling of unassigned io ports accesses

That is caused by the fact that QEMU reports to
OSPM that device is present by setting 5th bit in
PII4XPM.pci_conf[0x67] register when COM2 doesn't
exist.

It happens due to memory_region_present(io_as, 0x2f8)
returning false positive since 0x2f8 address eventually
translates into catchall io_as address space.

Fix memory_region_present(parent, addr) by returning
true only if addr maps into a MemoryRegion within
parent (excluding parent itself), to match its
doc comment.

While at it fix copy/paste error in
memory_region_present() doc comment.

Note: this is a temporary hack: we really need better handling for
unassigned regions, we should avoid fallback regions since they are bad
for performance (breaking radix tree assumption that the data structure
is sparsely populated); for memory we need to fix this to implement PCI
master abort properly, anyway.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/exec/memory.h | 6 +++---
 memory.c              | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 296d6ab..a5eb4c8 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -838,13 +838,13 @@ void memory_region_set_alias_offset(MemoryRegion *mr,
                                     hwaddr offset);
 
 /**
- * memory_region_present: translate an address/size relative to a
- * MemoryRegion into a #MemoryRegionSection.
+ * memory_region_present: checks if an address relative to a @parent
+ * translates into #MemoryRegion within @parent
  *
  * Answer whether a #MemoryRegion within @parent covers the address
  * @addr.
  *
- * @parent: a MemoryRegion within which @addr is a relative address
+ * @parent: a #MemoryRegion within which @addr is a relative address
  * @addr: the area within @parent to be searched
  */
 bool memory_region_present(MemoryRegion *parent, hwaddr addr);
diff --git a/memory.c b/memory.c
index 59ecc28..3f1df23 100644
--- a/memory.c
+++ b/memory.c
@@ -1562,7 +1562,7 @@ static FlatRange *flatview_lookup(FlatView *view, AddrRange addr)
 bool memory_region_present(MemoryRegion *parent, hwaddr addr)
 {
     MemoryRegion *mr = memory_region_find(parent, addr, 1).mr;
-    if (!mr) {
+    if (!mr || (mr == parent)) {
         return false;
     }
     memory_region_unref(mr);
-- 
MST