[Qemu-devel] [PATCH for-2.1 v2 1/2] migration: load smaller RAMBlock to a bigger one if permitted

[Igor Mammedov <imammedo@redhat.com>]

Add API to mark memory region as extend-able on migration,
to allow migration code to load smaller RAMBlock into
a bigger one on destination QEMU instance.

This will allow to fix broken migration from QEMU 1.7/2.0 to
QEMU 2.1 due to  ACPI tables size changes across 1.7/2.0/2.1
versions by marking ACPI tables ROM blob as extend-able.
So that smaller tables from previous version could be always
migrated to a bigger rom blob on new version.

Credits-for-idea: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
v2:
  fixed patch as suggested by Laszlo
---
 arch_init.c             | 22 +++++++++++++++++-----
 exec.c                  |  8 ++++++++
 include/exec/memory.h   | 11 +++++++++++
 include/exec/ram_addr.h |  3 +++
 memory.c                |  5 +++++
 5 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/arch_init.c b/arch_init.c
index 8ddaf35..2c0c238 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -1071,11 +1071,23 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
 
                 QTAILQ_FOREACH(block, &ram_list.blocks, next) {
                     if (!strncmp(id, block->idstr, sizeof(id))) {
-                        if (block->length != length) {
-                            error_report("Length mismatch: %s: " RAM_ADDR_FMT
-                                         " in != " RAM_ADDR_FMT, id, length,
-                                         block->length);
-                            ret =  -EINVAL;
+                        if (block->flags & RAM_EXTENDABLE_ON_MIGRATE) {
+                            if (block->length < length) {
+                                error_report("Length too big: %s: " RAM_ADDR_FMT
+                                             " in > " RAM_ADDR_FMT, id, length,
+                                             block->length);
+                                ret =  -EINVAL;
+                            } else {
+                                memset(block->host, 0, block->length);
+                            }
+                        } else {
+                            if (block->length != length) {
+                                error_report("Length mismatch: %s: "
+                                             RAM_ADDR_FMT " in != "
+                                             RAM_ADDR_FMT,
+                                             id, length, block->length);
+                                ret =  -EINVAL;
+                            }
                         }
                         break;
                     }
diff --git a/exec.c b/exec.c
index 765bd94..02536f8e 100644
--- a/exec.c
+++ b/exec.c
@@ -1214,6 +1214,14 @@ void qemu_ram_unset_idstr(ram_addr_t addr)
     }
 }
 
+void qemu_ram_set_extendable_on_migration(ram_addr_t addr)
+{
+    RAMBlock *block = find_ram_block(addr);
+
+    assert(block != NULL);
+    block->flags |= RAM_EXTENDABLE_ON_MIGRATE;
+}
+
 static int memory_try_enable_merging(void *addr, size_t len)
 {
     if (!qemu_opt_get_bool(qemu_get_machine_opts(), "mem-merge", true)) {
diff --git a/include/exec/memory.h b/include/exec/memory.h
index e2c8e3e..f96ddbb 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -894,6 +894,17 @@ bool memory_region_present(MemoryRegion *container, hwaddr addr);
 bool memory_region_is_mapped(MemoryRegion *mr);
 
 /**
+ * memory_region_permit_extendable_migration: marks #MemoryRegion
+ * as extendable on migration, allowing the migration code to load
+ * source memory block of smaller size than destination memory block
+ * at migration time
+ *
+ * @mr: a #MemoryRegion whose #RAMBlock should be marked as
+ *      extendable on migration
+ */
+void memory_region_permit_extendable_migration(MemoryRegion *mr);
+
+/**
  * memory_region_find: translate an address/size relative to a
  * MemoryRegion into a #MemoryRegionSection.
  *
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index 6593be1..7a6b782 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -34,6 +34,9 @@ void *qemu_get_ram_ptr(ram_addr_t addr);
 void qemu_ram_free(ram_addr_t addr);
 void qemu_ram_free_from_ptr(ram_addr_t addr);
 
+#define RAM_EXTENDABLE_ON_MIGRATE (1U << 31)
+void qemu_ram_set_extendable_on_migration(ram_addr_t addr);
+
 static inline bool cpu_physical_memory_get_dirty(ram_addr_t start,
                                                  ram_addr_t length,
                                                  unsigned client)
diff --git a/memory.c b/memory.c
index 64d7176..744c746 100644
--- a/memory.c
+++ b/memory.c
@@ -1791,6 +1791,11 @@ bool memory_region_is_mapped(MemoryRegion *mr)
     return mr->container ? true : false;
 }
 
+void memory_region_permit_extendable_migration(MemoryRegion *mr)
+{
+    qemu_ram_set_extendable_on_migration(mr->ram_addr);
+}
+
 MemoryRegionSection memory_region_find(MemoryRegion *mr,
                                        hwaddr addr, uint64_t size)
 {
-- 
1.8.3.1