[Qemu-devel] [PATCH v7 26/42] postcopy: Incoming initialisation

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

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

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
---
 include/migration/migration.h    |   3 +
 include/migration/postcopy-ram.h |  12 ++++
 migration/postcopy-ram.c         | 116 +++++++++++++++++++++++++++++++++++++++
 migration/ram.c                  |  11 ++++
 migration/savevm.c               |   4 ++
 trace-events                     |   2 +
 6 files changed, 148 insertions(+)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 4c6cf95..98e2568 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -69,6 +69,8 @@ struct MigrationIncomingState {
      */
     QemuEvent      main_thread_load_event;
 
+    /* For the kernel to send us notifications */
+    int            userfault_fd;
     QEMUFile *return_path;
     QemuMutex      rp_mutex;    /* We send replies from multiple threads */
     PostcopyState postcopy_state;
@@ -195,6 +197,7 @@ 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, uint64_t end);
+int ram_postcopy_incoming_init(MigrationIncomingState *mis);
 
 /**
  * @migrate_add_blocker - prevent migration from proceeding
diff --git a/include/migration/postcopy-ram.h b/include/migration/postcopy-ram.h
index 1d38f76..4192108 100644
--- a/include/migration/postcopy-ram.h
+++ b/include/migration/postcopy-ram.h
@@ -17,6 +17,18 @@
 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 memory start..end inclusive.
  * We can assume that if we've been called postcopy_ram_hosttest returned true
  */
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index 9c76472..35c87b4 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -177,6 +177,111 @@ 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_area(const char *block_name, void *host_addr,
+                     ram_addr_t offset, ram_addr_t length, void *opaque)
+{
+    MigrationIncomingState *mis = opaque;
+
+    trace_postcopy_init_area(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, (host_addr + length - 1))) {
+        return -1;
+    }
+
+    /*
+     * We also need the area to be normal 4k pages, not huge pages
+     * (otherwise we can't be sure we can atomically place the
+     * 4k page in later).  THP might come along and map a 2MB page
+     * and when it's partially accessed in precopy it might not break
+     * it down, but leave a 2MB zero'd page.
+     */
+#ifdef MADV_NOHUGEPAGE
+    if (madvise(host_addr, length, MADV_NOHUGEPAGE)) {
+        error_report("%s: NOHUGEPAGE: %s", __func__, strerror(errno));
+        return -1;
+    }
+#endif
+
+    return 0;
+}
+
+/*
+ * At the end of migration, undo the effects of init_area
+ * opaque should be the MIS.
+ */
+static int cleanup_area(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_area(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_area, 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_area, mis)) {
+        return -1;
+    }
+
+    return 0;
+}
+
 #else
 /* No target OS support, stubs just fail */
 
@@ -186,6 +291,17 @@ 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);
+}
+
 int postcopy_ram_discard_range(MigrationIncomingState *mis, uint8_t *start,
                                uint8_t *end)
 {
diff --git a/migration/ram.c b/migration/ram.c
index 8e681f2..f7d957e 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1667,6 +1667,17 @@ 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;
diff --git a/migration/savevm.c b/migration/savevm.c
index e6398dd..f4de52d 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1238,6 +1238,10 @@ static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis,
         return -1;
     }
 
+    if (ram_postcopy_incoming_init(mis)) {
+        return -1;
+    }
+
     postcopy_state_set(mis, POSTCOPY_INCOMING_ADVISE);
 
     return 0;
diff --git a/trace-events b/trace-events
index 5e8a120..2ffc1c6 100644
--- a/trace-events
+++ b/trace-events
@@ -1498,7 +1498,9 @@ rdma_start_outgoing_migration_after_rdma_source_init(void) ""
 
 # migration/postcopy-ram.c
 postcopy_discard_send_finish(const char *ramblock, int nwords, int ncmds) "%s mask words sent=%d in %d commands"
+postcopy_cleanup_area(const char *ramblock, void *host_addr, size_t offset, size_t length) "%s: %p offset=%zx length=%zx"
 postcopy_ram_discard_range(void *start, void *end) "%p,%p"
+postcopy_init_area(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"
-- 
2.4.3