migration: discard non-migratable RAMBlocks

On the POWER9 processor, the XIVE interrupt controller can control
interrupt sources using MMIO to trigger events, to EOI or to turn off
the sources. Priority management and interrupt acknowledgment is also
controlled by MMIO in the presenter sub-engine.

These MMIO regions are exposed to guests in QEMU with a set of 'ram
device' memory mappings, similarly to VFIO, and the VMAs are populated
dynamically with the appropriate pages using a fault handler.

But, these regions are an issue for migration. We need to discard the
associated RAMBlocks from the RAM state on the source VM and let the
destination VM rebuild the memory mappings on the new host in the
post_load() operation just before resuming the system.

To achieve this goal, the following introduces a new RAMBlock flag
RAM_MIGRATABLE which is updated in the vmstate_register_ram() and
vmstate_unregister_ram() routines. This flag is then used by the
migration to identify RAMBlocks to discard on the source. Some checks
are also performed on the destination to make sure nothing invalid was
sent.

This change impacts the boston, malta and jazz mips boards for which
migration compatibility is broken.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 38 insertions, 0 deletions

diff --git a/exec.c b/exec.c
index c30f905598..af90e914cf 100644
--- a/exec.c
+++ b/exec.c
@@ -104,6 +104,9 @@ static MemoryRegion io_mem_unassigned;
  * (Set during postcopy)
  */
 #define RAM_UF_ZEROPAGE (1 << 3)
+
+/* RAM can be migrated */
+#define RAM_MIGRATABLE (1 << 4)
 #endif
 
 #ifdef TARGET_PAGE_BITS_VARY
@@ -1838,6 +1841,21 @@ void qemu_ram_set_uf_zeroable(RAMBlock *rb)
     rb->flags |= RAM_UF_ZEROPAGE;
 }
 
+bool qemu_ram_is_migratable(RAMBlock *rb)
+{
+    return rb->flags & RAM_MIGRATABLE;
+}
+
+void qemu_ram_set_migratable(RAMBlock *rb)
+{
+    rb->flags |= RAM_MIGRATABLE;
+}
+
+void qemu_ram_unset_migratable(RAMBlock *rb)
+{
+    rb->flags &= ~RAM_MIGRATABLE;
+}
+
 /* Called with iothread lock held.  */
 void qemu_ram_set_idstr(RAMBlock *new_block, const char *name, DeviceState *dev)
 {
@@ -3893,6 +3911,26 @@ int qemu_ram_foreach_block(RAMBlockIterFunc func, void *opaque)
     return ret;
 }
 
+int qemu_ram_foreach_migratable_block(RAMBlockIterFunc func, void *opaque)
+{
+    RAMBlock *block;
+    int ret = 0;
+
+    rcu_read_lock();
+    RAMBLOCK_FOREACH(block) {
+        if (!qemu_ram_is_migratable(block)) {
+            continue;
+        }
+        ret = func(block->idstr, block->host, block->offset,
+                   block->used_length, opaque);
+        if (ret) {
+            break;
+        }
+    }
+    rcu_read_unlock();
+    return ret;
+}
+
 /*
  * Unmap pages of memory from start to start+length such that
  * they a) read as 0, b) Trigger whatever fault mechanism