[PULL 6/7] migration/rdma: Try to register On-Demand Paging memory region

[Juan Quintela <quintela@redhat.com>]

From: Li Zhijian <lizhijian@cn.fujitsu.com>

Previously, for the fsdax mem-backend-file, it will register failed with
Operation not supported. In this case, we can try to register it with
On-Demand Paging[1] like what rpma_mr_reg() does on rpma[2].

[1]: https://community.mellanox.com/s/article/understanding-on-demand-paging--odp-x
[2]: http://pmem.io/rpma/manpages/v0.9.0/rpma_mr_reg.3

CC: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Reviewed-by: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 migration/rdma.c       | 73 ++++++++++++++++++++++++++++++------------
 migration/trace-events |  1 +
 2 files changed, 54 insertions(+), 20 deletions(-)

diff --git a/migration/rdma.c b/migration/rdma.c
index 5c2d113aa9..eb80431aae 100644
--- a/migration/rdma.c
+++ b/migration/rdma.c
@@ -1117,19 +1117,47 @@ static int qemu_rdma_alloc_qp(RDMAContext *rdma)
     return 0;
 }
 
+/* Check whether On-Demand Paging is supported by RDAM device */
+static bool rdma_support_odp(struct ibv_context *dev)
+{
+    struct ibv_device_attr_ex attr = {0};
+    int ret = ibv_query_device_ex(dev, NULL, &attr);
+    if (ret) {
+        return false;
+    }
+
+    if (attr.odp_caps.general_caps & IBV_ODP_SUPPORT) {
+        return true;
+    }
+
+    return false;
+}
+
 static int qemu_rdma_reg_whole_ram_blocks(RDMAContext *rdma)
 {
     int i;
     RDMALocalBlocks *local = &rdma->local_ram_blocks;
 
     for (i = 0; i < local->nb_blocks; i++) {
+        int access = IBV_ACCESS_LOCAL_WRITE | IBV_ACCESS_REMOTE_WRITE;
+
         local->block[i].mr =
             ibv_reg_mr(rdma->pd,
                     local->block[i].local_host_addr,
-                    local->block[i].length,
-                    IBV_ACCESS_LOCAL_WRITE |
-                    IBV_ACCESS_REMOTE_WRITE
+                    local->block[i].length, access
                     );
+
+        if (!local->block[i].mr &&
+            errno == ENOTSUP && rdma_support_odp(rdma->verbs)) {
+                access |= IBV_ACCESS_ON_DEMAND;
+                /* register ODP mr */
+                local->block[i].mr =
+                    ibv_reg_mr(rdma->pd,
+                               local->block[i].local_host_addr,
+                               local->block[i].length, access);
+                trace_qemu_rdma_register_odp_mr(local->block[i].block_name);
+        }
+
         if (!local->block[i].mr) {
             perror("Failed to register local dest ram block!");
             break;
@@ -1215,28 +1243,33 @@ static int qemu_rdma_register_and_get_keys(RDMAContext *rdma,
      */
     if (!block->pmr[chunk]) {
         uint64_t len = chunk_end - chunk_start;
+        int access = rkey ? IBV_ACCESS_LOCAL_WRITE | IBV_ACCESS_REMOTE_WRITE :
+                     0;
 
         trace_qemu_rdma_register_and_get_keys(len, chunk_start);
 
-        block->pmr[chunk] = ibv_reg_mr(rdma->pd,
-                chunk_start, len,
-                (rkey ? (IBV_ACCESS_LOCAL_WRITE |
-                        IBV_ACCESS_REMOTE_WRITE) : 0));
-
-        if (!block->pmr[chunk]) {
-            perror("Failed to register chunk!");
-            fprintf(stderr, "Chunk details: block: %d chunk index %d"
-                            " start %" PRIuPTR " end %" PRIuPTR
-                            " host %" PRIuPTR
-                            " local %" PRIuPTR " registrations: %d\n",
-                            block->index, chunk, (uintptr_t)chunk_start,
-                            (uintptr_t)chunk_end, host_addr,
-                            (uintptr_t)block->local_host_addr,
-                            rdma->total_registrations);
-            return -1;
+        block->pmr[chunk] = ibv_reg_mr(rdma->pd, chunk_start, len, access);
+        if (!block->pmr[chunk] &&
+            errno == ENOTSUP && rdma_support_odp(rdma->verbs)) {
+            access |= IBV_ACCESS_ON_DEMAND;
+            /* register ODP mr */
+            block->pmr[chunk] = ibv_reg_mr(rdma->pd, chunk_start, len, access);
+            trace_qemu_rdma_register_odp_mr(block->block_name);
         }
-        rdma->total_registrations++;
     }
+    if (!block->pmr[chunk]) {
+        perror("Failed to register chunk!");
+        fprintf(stderr, "Chunk details: block: %d chunk index %d"
+                        " start %" PRIuPTR " end %" PRIuPTR
+                        " host %" PRIuPTR
+                        " local %" PRIuPTR " registrations: %d\n",
+                        block->index, chunk, (uintptr_t)chunk_start,
+                        (uintptr_t)chunk_end, host_addr,
+                        (uintptr_t)block->local_host_addr,
+                        rdma->total_registrations);
+        return -1;
+    }
+    rdma->total_registrations++;
 
     if (lkey) {
         *lkey = block->pmr[chunk]->lkey;
diff --git a/migration/trace-events b/migration/trace-events
index a1c0f034ab..5f6aa580de 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -212,6 +212,7 @@ qemu_rdma_poll_write(const char *compstr, int64_t comp, int left, uint64_t block
 qemu_rdma_poll_other(const char *compstr, int64_t comp, int left) "other completion %s (%" PRId64 ") received left %d"
 qemu_rdma_post_send_control(const char *desc) "CONTROL: sending %s.."
 qemu_rdma_register_and_get_keys(uint64_t len, void *start) "Registering %" PRIu64 " bytes @ %p"
+qemu_rdma_register_odp_mr(const char *name) "Try to register On-Demand Paging memory region: %s"
 qemu_rdma_registration_handle_compress(int64_t length, int index, int64_t offset) "Zapping zero chunk: %" PRId64 " bytes, index %d, offset %" PRId64
 qemu_rdma_registration_handle_finished(void) ""
 qemu_rdma_registration_handle_ram_blocks(void) ""
-- 
2.31.1