postcopy: Incoming initialisation

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

include/migration/migration.h

@@ -86,6 +86,8 @@ struct MigrationIncomingState {
      */
     QemuEvent main_thread_load_event;
 
+    /* For the kernel to send us notifications */
+    int       userfault_fd;
     QEMUFile *to_src_file;
     QemuMutex rp_mutex;    /* We send replies from multiple threads */
 
@@ -204,6 +206,7 @@ int ram_postcopy_send_discard_bitmap(MigrationState *ms);
 /* For incoming postcopy discard */
 int ram_discard_range(MigrationIncomingState *mis, const char *block_name,
                       uint64_t start, size_t length);
+int ram_postcopy_incoming_init(MigrationIncomingState *mis);
 
 /**
  * @migrate_add_blocker - prevent migration from proceeding

include/migration/postcopy-ram.h

@@ -16,6 +16,18 @@
 /* Return true if the host supports everything we need to do postcopy-ram */
 bool postcopy_ram_supported_by_host(void);
 
+/*
+ * Initialise postcopy-ram, setting the RAM to a state where we can go into
+ * postcopy later; must be called prior to any precopy.
+ * called from ram.c's similarly named ram_postcopy_incoming_init
+ */
+int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages);
+
+/*
+ * At the end of a migration where postcopy_ram_incoming_init was called.
+ */
+int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis);
+
 /*
  * Discard the contents of 'length' bytes from 'start'
  * We can assume that if we've been called postcopy_ram_hosttest returned true

migration/postcopy-ram.c

@@ -184,6 +184,97 @@ int postcopy_ram_discard_range(MigrationIncomingState *mis, uint8_t *start,
     return 0;
 }
 
+/*
+ * Setup an area of RAM so that it *can* be used for postcopy later; this
+ * must be done right at the start prior to pre-copy.
+ * opaque should be the MIS.
+ */
+static int init_range(const char *block_name, void *host_addr,
+                      ram_addr_t offset, ram_addr_t length, void *opaque)
+{
+    MigrationIncomingState *mis = opaque;
+
+    trace_postcopy_init_range(block_name, host_addr, offset, length);
+
+    /*
+     * We need the whole of RAM to be truly empty for postcopy, so things
+     * like ROMs and any data tables built during init must be zero'd
+     * - we're going to get the copy from the source anyway.
+     * (Precopy will just overwrite this data, so doesn't need the discard)
+     */
+    if (postcopy_ram_discard_range(mis, host_addr, length)) {
+        return -1;
+    }
+
+    return 0;
+}
+
+/*
+ * At the end of migration, undo the effects of init_range
+ * opaque should be the MIS.
+ */
+static int cleanup_range(const char *block_name, void *host_addr,
+                        ram_addr_t offset, ram_addr_t length, void *opaque)
+{
+    MigrationIncomingState *mis = opaque;
+    struct uffdio_range range_struct;
+    trace_postcopy_cleanup_range(block_name, host_addr, offset, length);
+
+    /*
+     * We turned off hugepage for the precopy stage with postcopy enabled
+     * we can turn it back on now.
+     */
+#ifdef MADV_HUGEPAGE
+    if (madvise(host_addr, length, MADV_HUGEPAGE)) {
+        error_report("%s HUGEPAGE: %s", __func__, strerror(errno));
+        return -1;
+    }
+#endif
+
+    /*
+     * We can also turn off userfault now since we should have all the
+     * pages.   It can be useful to leave it on to debug postcopy
+     * if you're not sure it's always getting every page.
+     */
+    range_struct.start = (uintptr_t)host_addr;
+    range_struct.len = length;
+
+    if (ioctl(mis->userfault_fd, UFFDIO_UNREGISTER, &range_struct)) {
+        error_report("%s: userfault unregister %s", __func__, strerror(errno));
+
+        return -1;
+    }
+
+    return 0;
+}
+
+/*
+ * Initialise postcopy-ram, setting the RAM to a state where we can go into
+ * postcopy later; must be called prior to any precopy.
+ * called from arch_init's similarly named ram_postcopy_incoming_init
+ */
+int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages)
+{
+    if (qemu_ram_foreach_block(init_range, mis)) {
+        return -1;
+    }
+
+    return 0;
+}
+
+/*
+ * At the end of a migration where postcopy_ram_incoming_init was called.
+ */
+int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
+{
+    /* TODO: Join the fault thread once we're sure it will exit */
+    if (qemu_ram_foreach_block(cleanup_range, mis)) {
+        return -1;
+    }
+
+    return 0;
+}
+
 #else
 /* No target OS support, stubs just fail */
 bool postcopy_ram_supported_by_host(void)
@@ -192,10 +283,23 @@ bool postcopy_ram_supported_by_host(void)
     return false;
 }
 
+int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages)
+{
+    error_report("postcopy_ram_incoming_init: No OS support");
+    return -1;
+}
+
+int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
+{
+    assert(0);
+    return -1;
+}
+
 int postcopy_ram_discard_range(MigrationIncomingState *mis, uint8_t *start,
                                size_t length)
 {
     assert(0);
+    return -1;
 }
 #endif
 

migration/ram.c

@@ -1794,6 +1794,17 @@ static void decompress_data_with_multi_threads(uint8_t *compbuf,
     }
 }
 
+/*
+ * Allocate data structures etc needed by incoming migration with postcopy-ram
+ * postcopy-ram's similarly names postcopy_ram_incoming_init does the work
+ */
+int ram_postcopy_incoming_init(MigrationIncomingState *mis)
+{
+    size_t ram_pages = last_ram_offset() >> TARGET_PAGE_BITS;
+
+    return postcopy_ram_incoming_init(mis, ram_pages);
+}
+
 static int ram_load(QEMUFile *f, void *opaque, int version_id)
 {
     int flags = 0, ret = 0;

migration/savevm.c

@@ -1281,6 +1281,12 @@ static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis)
         return -1;
     }
 
+    if (ram_postcopy_incoming_init(mis)) {
+        return -1;
+    }
+
+    postcopy_state_set(POSTCOPY_INCOMING_ADVISE);
+
     return 0;
 }
 

trace-events

@@ -1537,6 +1537,8 @@ rdma_start_outgoing_migration_after_rdma_source_init(void) ""
 postcopy_discard_send_finish(const char *ramblock, int nwords, int ncmds) "%s mask words sent=%d in %d commands"
 postcopy_discard_send_range(const char *ramblock, unsigned long start, unsigned long length) "%s:%lx/%lx"
 postcopy_ram_discard_range(void *start, size_t length) "%p,+%zx"
+postcopy_cleanup_range(const char *ramblock, void *host_addr, size_t offset, size_t length) "%s: %p offset=%zx length=%zx"
+postcopy_init_range(const char *ramblock, void *host_addr, size_t offset, size_t length) "%s: %p offset=%zx length=%zx"
 
 # kvm-all.c
 kvm_ioctl(int type, void *arg) "type 0x%x, arg %p"