[Xen-devel] [PATCH v2] xen-hvm: ignore background I/O sections

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

Since Xen will correctly handle accesses to unimplemented I/O ports (by
returning all 1's for reads and ignoring writes) there is no need for
QEMU to register backgroud I/O sections.

This patch therefore adds checks to xen_io_add/del so that sections with
memory-region ops pointing at 'unassigned_io_ops' are ignored.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---

v2:
 - Add missing braces
---
 xen-hvm.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/xen-hvm.c b/xen-hvm.c
index 039680a..8ab44f0 100644
--- a/xen-hvm.c
+++ b/xen-hvm.c
@@ -510,8 +510,12 @@ static void xen_io_add(MemoryListener *listener,
                        MemoryRegionSection *section)
 {
     XenIOState *state = container_of(listener, XenIOState, io_listener);
+    MemoryRegion *mr = section->mr;
 
-    memory_region_ref(section->mr);
+    if (mr->ops == &unassigned_io_ops)
+        return;
+
+    memory_region_ref(mr);
 
     xen_map_io_section(xen_xc, xen_domid, state->ioservid, section);
 }
@@ -520,10 +524,14 @@ static void xen_io_del(MemoryListener *listener,
                        MemoryRegionSection *section)
 {
     XenIOState *state = container_of(listener, XenIOState, io_listener);
+    MemoryRegion *mr = section->mr;
+
+    if (mr->ops == &unassigned_io_ops)
+        return;
 
     xen_unmap_io_section(xen_xc, xen_domid, state->ioservid, section);
 
-    memory_region_unref(section->mr);
+    memory_region_unref(mr);
 }
 
 static void xen_device_realize(DeviceListener *listener,
-- 
2.1.4


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