[Qemu-devel] [RFC PATCH 4/8] memory: ref/unref memory across address_space_map/unmap

[Paolo Bonzini <pbonzini@redhat.com>]

The iothread mutex might be released between map and unmap, so the
mapped region might disappear.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 exec.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/exec.c b/exec.c
index 54b57fc..54ed203 100644
--- a/exec.c
+++ b/exec.c
@@ -2077,6 +2077,7 @@ void cpu_physical_memory_write_rom(hwaddr addr,
 }
 
 typedef struct {
+    MemoryRegion *mr;
     void *buffer;
     hwaddr addr;
     hwaddr len;
@@ -2171,15 +2172,18 @@ void *address_space_map(AddressSpace *as,
             bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, TARGET_PAGE_SIZE);
             bounce.addr = addr;
             bounce.len = l;
+            bounce.mr = section->mr;
             if (!is_write) {
                 address_space_read(as, addr, bounce.buffer, l);
             }
 
             *plen = l;
+            memory_region_ref(section->mr);
             return bounce.buffer;
         }
         if (!todo) {
             raddr = memory_region_get_ram_addr(section->mr) + xlat;
+            memory_region_ref(section->mr);
         } else {
             if (memory_region_get_ram_addr(section->mr) + xlat != raddr + todo) {
                 break;
@@ -2204,8 +2208,12 @@ void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
                          int is_write, hwaddr access_len)
 {
     if (buffer != bounce.buffer) {
+        MemoryRegion *mr;
+        ram_addr_t addr1;
+
+        mr = qemu_ram_addr_from_host(buffer, &addr1);
+        assert(mr);
         if (is_write) {
-            ram_addr_t addr1 = qemu_ram_addr_from_host_nofail(buffer);
             while (access_len) {
                 unsigned l;
                 l = TARGET_PAGE_SIZE;
@@ -2219,6 +2227,7 @@ void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
         if (xen_enabled()) {
             xen_invalidate_map_cache_entry(buffer);
         }
+        memory_region_unref(mr);
         return;
     }
     if (is_write) {
@@ -2226,6 +2235,7 @@ void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
     }
     qemu_vfree(bounce.buffer);
     bounce.buffer = NULL;
+    memory_region_unref(bounce.mr);
     cpu_notify_map_clients();
 }
 
-- 
1.7.1