xen/mapcache: add an ability to create dummy mappings

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>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

1 files changed, 36 insertions, 8 deletions

diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c
index e60156c04f..39cb511117 100644
--- a/hw/i386/xen/xen-mapcache.c
+++ b/hw/i386/xen/xen-mapcache.c
@@ -53,6 +53,8 @@ typedef struct MapCacheEntry {
     uint8_t *vaddr_base;
     unsigned long *valid_mapping;
     uint8_t lock;
+#define XEN_MAPCACHE_ENTRY_DUMMY (1 << 0)
+    uint8_t flags;
     hwaddr size;
     struct MapCacheEntry *next;
 } MapCacheEntry;
@@ -150,7 +152,8 @@ 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 +180,25 @@ 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;
@@ -190,6 +207,12 @@ static void xen_remap_bucket(MapCacheEntry *entry,
     entry->valid_mapping = (unsigned long *) g_malloc0(sizeof(unsigned long) *
             BITS_TO_LONGS(size >> XC_PAGE_SHIFT));
 
+    if (dummy) {
+        entry->flags |= XEN_MAPCACHE_ENTRY_DUMMY;
+    } else {
+        entry->flags &= ~(XEN_MAPCACHE_ENTRY_DUMMY);
+    }
+
     ram_block_notify_add(entry->vaddr_base, entry->size);
     bitmap_zero(entry->valid_mapping, nb_pfn);
     for (i = 0; i < nb_pfn; i++) {
@@ -211,6 +234,7 @@ 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 +286,14 @@ 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 +306,10 @@ tryagain:
             translated = true;
             goto tryagain;
         }
+        if (!dummy && runstate_check(RUN_STATE_INMIGRATE)) {
+            dummy = true;
+            goto tryagain;
+        }
         trace_xen_map_cache_return(NULL);
         return NULL;
     }