[Qemu-devel] [PATCH] memory_region_present: return false if address is not found in child MemoryRegion

[Igor Mammedov]

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

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.

Signed-off-by: Igor Mammedov <address@hidden>
---
 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);
-- 
1.7.1