[Qemu-devel] [RFC 14/29] vhost+postcopy: Register new regions with the ufd

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

When new regions are sent to the client using SET_MEM_TABLE, register
them with the userfaultfd.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 contrib/libvhost-user/libvhost-user.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index 6de339fb7a..be7470e3a9 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -450,6 +450,39 @@ vu_set_mem_table_exec(VuDev *dev, VhostUserMsg *vmsg)
                    dev_region->mmap_addr);
         }
 
+        if (dev->postcopy_listening) {
+            /* We should already have an open ufd need to mark each memory
+             * range as ufd.
+             * Note: Do we need any madvises? Well it's not been accessed
+             * yet, still probably need no THP to be safe, discard to be safe?
+             */
+            struct uffdio_register reg_struct;
+            /* Note: We might need to go back to using mmap_addr and
+             * len + mmap_offset for * huge pages, but then we do hope not to
+             * see accesses in that area below the offset
+             */
+            reg_struct.range.start = (uintptr_t)(dev_region->mmap_addr +
+                                                 dev_region->mmap_offset);
+            reg_struct.range.len = dev_region->size;
+            reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
+
+            if (ioctl(dev->postcopy_ufd, UFFDIO_REGISTER, &reg_struct)) {
+                vu_panic(dev, "%s: Failed to userfault region %d: (ufd=%d)%s\n",
+                         __func__, i, strerror(errno), dev->postcopy_ufd);
+                continue;
+            }
+            if (!(reg_struct.ioctls & ((__u64)1 << _UFFDIO_COPY))) {
+                vu_panic(dev, "%s Region (%d) doesn't support COPY",
+                         __func__, i);
+                continue;
+            }
+            DPRINT("%s: region %d: Registered userfault for %llx + %llx\n",
+                    __func__, i, reg_struct.range.start, reg_struct.range.len);
+            /* TODO: Stash 'zero' support flags somewhere */
+            /* TODO: Get address back to QEMU */
+
+        }
+
         close(vmsg->fds[i]);
     }
 
-- 
2.13.0