vhost: improve region filtering

vhost memory management doesn't care about non-memory (e.g. PIO) or non-RAM
regions.  Adjust the filtering to reflect that, and move it earlier so it
applies to mem_sections too.

Signed-off-by: Avi Kivity <avi@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>

hw/vhost.c

diff --git a/hw/vhost.c b/hw/vhost.c
index d924fb0..19a7b5c 100644
--- a/hw/vhost.c
+++ b/hw/vhost.c
@@ -15,6 +15,7 @@
 #include "hw/hw.h"
 #include "range.h"
 #include <linux/vhost.h>
+#include "exec-memory.h"
 
 static void vhost_dev_sync_region(struct vhost_dev *dev,
                                   MemoryRegionSection *section,
@@ -365,10 +366,6 @@
     int r;
     void *ram;
 
-    if (!memory_region_is_ram(section->mr)) {
-        return;
-    }
-
     dev->mem = g_realloc(dev->mem, s);
 
     if (log_dirty) {
@@ -430,12 +427,22 @@
     }
 }
 
+static bool vhost_section(MemoryRegionSection *section)
+{
+    return section->address_space == get_system_memory()
+        && memory_region_is_ram(section->mr);
+}
+
 static void vhost_region_add(MemoryListener *listener,
                              MemoryRegionSection *section)
 {
     struct vhost_dev *dev = container_of(listener, struct vhost_dev,
                                          memory_listener);
 
+    if (!vhost_section(section)) {
+        return;
+    }
+
     ++dev->n_mem_sections;
     dev->mem_sections = g_renew(MemoryRegionSection, dev->mem_sections,
                                 dev->n_mem_sections);
@@ -450,6 +457,10 @@
                                          memory_listener);
     int i;
 
+    if (!vhost_section(section)) {
+        return;
+    }
+
     vhost_set_memory(listener, section, false);
     for (i = 0; i < dev->n_mem_sections; ++i) {
         if (dev->mem_sections[i].offset_within_address_space