vhost+postcopy: Send address back to qemu

We need a better way, but at the moment we need the address of the
mappings sent back to qemu so it can interpret the messages on the
userfaultfd it reads.

This is done as a 3 stage set:
   QEMU -> client
      set_mem_table

   mmap stuff, get addresses

   client -> qemu
       here are the addresses

   qemu -> client
       OK - now you can use them

That ensures that qemu has registered the new addresses in it's
userfault code before the client starts accessing them.

Note: We don't ask for the default 'ack' reply since we've got our own.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 65 insertions, 2 deletions

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index b6757eb..1603d70 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -174,6 +174,7 @@ struct vhost_user {
     int slave_fd;
     NotifierWithReturn postcopy_notifier;
     struct PostCopyFD  postcopy_fd;
+    uint64_t           postcopy_client_bases[VHOST_MEMORY_MAX_NREGIONS];
     /* True once we've entered postcopy_listen */
     bool               postcopy_listen;
 };
@@ -343,12 +344,15 @@ static int vhost_user_set_log_base(struct vhost_dev *dev, uint64_t base,
 static int vhost_user_set_mem_table_postcopy(struct vhost_dev *dev,
                                              struct vhost_memory *mem)
 {
+    struct vhost_user *u = dev->opaque;
     int fds[VHOST_MEMORY_MAX_NREGIONS];
     int i, fd;
     size_t fd_num = 0;
     bool reply_supported = virtio_has_feature(dev->protocol_features,
                                               VHOST_USER_PROTOCOL_F_REPLY_ACK);
-    /* TODO: Add actual postcopy differences */
+    VhostUserMsg msg_reply;
+    int region_i, msg_i;
+
     VhostUserMsg msg = {
         .hdr.request = VHOST_USER_SET_MEM_TABLE,
         .hdr.flags = VHOST_USER_VERSION,
@@ -395,6 +399,64 @@ static int vhost_user_set_mem_table_postcopy(struct vhost_dev *dev,
         return -1;
     }
 
+    if (vhost_user_read(dev, &msg_reply) < 0) {
+        return -1;
+    }
+
+    if (msg_reply.hdr.request != VHOST_USER_SET_MEM_TABLE) {
+        error_report("%s: Received unexpected msg type."
+                     "Expected %d received %d", __func__,
+                     VHOST_USER_SET_MEM_TABLE, msg_reply.hdr.request);
+        return -1;
+    }
+    /* We're using the same structure, just reusing one of the
+     * fields, so it should be the same size.
+     */
+    if (msg_reply.hdr.size != msg.hdr.size) {
+        error_report("%s: Unexpected size for postcopy reply "
+                     "%d vs %d", __func__, msg_reply.hdr.size, msg.hdr.size);
+        return -1;
+    }
+
+    memset(u->postcopy_client_bases, 0,
+           sizeof(uint64_t) * VHOST_MEMORY_MAX_NREGIONS);
+
+    /* They're in the same order as the regions that were sent
+     * but some of the regions were skipped (above) if they
+     * didn't have fd's
+    */
+    for (msg_i = 0, region_i = 0;
+         region_i < dev->mem->nregions;
+        region_i++) {
+        if (msg_i < fd_num &&
+            msg_reply.payload.memory.regions[msg_i].guest_phys_addr ==
+            dev->mem->regions[region_i].guest_phys_addr) {
+            u->postcopy_client_bases[region_i] =
+                msg_reply.payload.memory.regions[msg_i].userspace_addr;
+            trace_vhost_user_set_mem_table_postcopy(
+                msg_reply.payload.memory.regions[msg_i].userspace_addr,
+                msg.payload.memory.regions[msg_i].userspace_addr,
+                msg_i, region_i);
+            msg_i++;
+        }
+    }
+    if (msg_i != fd_num) {
+        error_report("%s: postcopy reply not fully consumed "
+                     "%d vs %zd",
+                     __func__, msg_i, fd_num);
+        return -1;
+    }
+    /* Now we've registered this with the postcopy code, we ack to the client,
+     * because now we're in the position to be able to deal with any faults
+     * it generates.
+     */
+    /* TODO: Use this for failure cases as well with a bad value */
+    msg.hdr.size = sizeof(msg.payload.u64);
+    msg.payload.u64 = 0; /* OK */
+    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
+        return -1;
+    }
+
     if (reply_supported) {
         return process_message_reply(dev, &msg);
     }
@@ -411,7 +473,8 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
     size_t fd_num = 0;
     bool do_postcopy = u->postcopy_listen && u->postcopy_fd.handler;
     bool reply_supported = virtio_has_feature(dev->protocol_features,
-                                              VHOST_USER_PROTOCOL_F_REPLY_ACK);
+                                          VHOST_USER_PROTOCOL_F_REPLY_ACK) &&
+                                          !do_postcopy;
 
     if (do_postcopy) {
         /* Postcopy has enough differences that it's best done in it's own