[PATCH v4 07/21] migration/rdma: Use ram_block_discard_disable()

[David Hildenbrand]

RDMA will pin all guest memory (as documented in docs/rdma.txt). We want
to disable RAM block discards - however, to keep it simple use
ram_block_discard_is_required() instead of inhibiting.

Note: It is not sufficient to limit disabling to pin_all. Even when only
conditionally pinning 1 MB chunks, as soon as one page within such a
chunk was discarded and one page not, the discarded pages will be pinned
as well.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 migration/rdma.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/migration/rdma.c b/migration/rdma.c
index ec45d33ba3..bbe6f36627 100644
--- a/migration/rdma.c
+++ b/migration/rdma.c
@@ -29,6 +29,7 @@
 #include "qemu/sockets.h"
 #include "qemu/bitmap.h"
 #include "qemu/coroutine.h"
+#include "exec/memory.h"
 #include <sys/socket.h>
 #include <netdb.h>
 #include <arpa/inet.h>
@@ -4017,8 +4018,14 @@ void rdma_start_incoming_migration(const char 
*host_port, Error **errp)
     Error *local_err = NULL;
 
     trace_rdma_start_incoming_migration();
-    rdma = qemu_rdma_data_init(host_port, &local_err);
 
+    /* Avoid ram_block_discard_disable(), cannot change during migration. */
+    if (ram_block_discard_is_required()) {
+        error_setg(errp, "RDMA: cannot disable RAM discard");
+        return;
+    }
+
+    rdma = qemu_rdma_data_init(host_port, &local_err);
     if (rdma == NULL) {
         goto err;
     }
@@ -4067,10 +4074,17 @@ void rdma_start_outgoing_migration(void *opaque,
                             const char *host_port, Error **errp)
 {
     MigrationState *s = opaque;
-    RDMAContext *rdma = qemu_rdma_data_init(host_port, errp);
     RDMAContext *rdma_return_path = NULL;
+    RDMAContext *rdma;
     int ret = 0;
 
+    /* Avoid ram_block_discard_disable(), cannot change during migration. */
+    if (ram_block_discard_is_required()) {
+        error_setg(errp, "RDMA: cannot disable RAM discard");
+        return;
+    }
+
+    rdma = qemu_rdma_data_init(host_port, errp);
     if (rdma == NULL) {
         goto err;
     }
-- 
2.26.2