[Qemu-devel] [PATCH 2/4] xen/mapcache: add an ability to create dummy mappings

[Igor Druzhinin <igor.druzhinin@citrix.com>]

Dummys are simple anonymous mappings that are placed instead
of regular foreign mappings in certain situations when we need
to postpone the actual mapping but still have to give a
memory region to QEMU to play with.

This is planned to be used for restore on Xen.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
---
 hw/i386/xen/xen-mapcache.c | 36 ++++++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 8 deletions(-)

diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c
index e60156c..05050de 100644
--- a/hw/i386/xen/xen-mapcache.c
+++ b/hw/i386/xen/xen-mapcache.c
@@ -150,7 +150,8 @@ void xen_map_cache_init(phys_offset_to_gaddr_t f, void *opaque)
 
 static void xen_remap_bucket(MapCacheEntry *entry,
                              hwaddr size,
-                             hwaddr address_index)
+                             hwaddr address_index,
+                             bool dummy)
 {
     uint8_t *vaddr_base;
     xen_pfn_t *pfns;
@@ -177,11 +178,25 @@ static void xen_remap_bucket(MapCacheEntry *entry,
         pfns[i] = (address_index << (MCACHE_BUCKET_SHIFT-XC_PAGE_SHIFT)) + i;
     }
 
-    vaddr_base = xenforeignmemory_map(xen_fmem, xen_domid, PROT_READ|PROT_WRITE,
-                                      nb_pfn, pfns, err);
-    if (vaddr_base == NULL) {
-        perror("xenforeignmemory_map");
-        exit(-1);
+    if (!dummy) {
+        vaddr_base = xenforeignmemory_map(xen_fmem, xen_domid,
+                                           PROT_READ|PROT_WRITE,
+                                           nb_pfn, pfns, err);
+        if (vaddr_base == NULL) {
+            perror("xenforeignmemory_map");
+            exit(-1);
+        }
+    } else {
+        /*
+         * We create dummy mappings where we are unable to create a foreign
+         * mapping immediately due to certain circumstances (i.e. on resume now)
+         */
+        vaddr_base = mmap(NULL, size, PROT_READ|PROT_WRITE,
+                          MAP_ANON|MAP_SHARED, -1, 0);
+        if (vaddr_base == NULL) {
+            perror("mmap");
+            exit(-1);
+        }
     }
 
     entry->vaddr_base = vaddr_base;
@@ -211,6 +226,7 @@ static uint8_t *xen_map_cache_unlocked(hwaddr phys_addr, hwaddr size,
     hwaddr cache_size = size;
     hwaddr test_bit_size;
     bool translated = false;
+    bool dummy = false;
 
 tryagain:
     address_index  = phys_addr >> MCACHE_BUCKET_SHIFT;
@@ -262,14 +278,14 @@ tryagain:
     if (!entry) {
         entry = g_malloc0(sizeof (MapCacheEntry));
         pentry->next = entry;
-        xen_remap_bucket(entry, cache_size, address_index);
+        xen_remap_bucket(entry, cache_size, address_index, dummy);
     } else if (!entry->lock) {
         if (!entry->vaddr_base || entry->paddr_index != address_index ||
                 entry->size != cache_size ||
                 !test_bits(address_offset >> XC_PAGE_SHIFT,
                     test_bit_size >> XC_PAGE_SHIFT,
                     entry->valid_mapping)) {
-            xen_remap_bucket(entry, cache_size, address_index);
+            xen_remap_bucket(entry, cache_size, address_index, dummy);
         }
     }
 
@@ -282,6 +298,10 @@ tryagain:
             translated = true;
             goto tryagain;
         }
+        if (!dummy && runstate_check(RUN_STATE_INMIGRATE)) {
+            dummy = true;
+            goto tryagain;
+        }
         trace_xen_map_cache_return(NULL);
         return NULL;
     }
-- 
2.7.4