[Qemu-devel] [PATCH v4 31/47] postcopy: Incoming initialisation

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <address@hidden>

Signed-off-by: Dr. David Alan Gilbert <address@hidden>
---
 arch_init.c                      |  11 ++++
 include/migration/migration.h    |   1 +
 include/migration/postcopy-ram.h |  12 +++++
 migration.c                      |   1 +
 postcopy-ram.c                   | 110 ++++++++++++++++++++++++++++++++++++++-
 savevm.c                         |   4 ++
 6 files changed, 138 insertions(+), 1 deletion(-)

diff --git a/arch_init.c b/arch_init.c
index 030d189..4a03171 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -1345,6 +1345,17 @@ void ram_handle_compressed(void *host, uint8_t ch, 
uint64_t size)
     }
 }
 
+/*
+ * 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)
 {
     ram_addr_t addr;
diff --git a/include/migration/migration.h b/include/migration/migration.h
index 73d338e..be63c89 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -203,6 +203,7 @@ 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 2a39a03..8f237a2 100644
--- a/include/migration/postcopy-ram.h
+++ b/include/migration/postcopy-ram.h
@@ -19,6 +19,18 @@
 int postcopy_ram_hosttest(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 arch_init'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);
+
+/*
  * In 'advise' mode record that a page has been received.
  */
 void postcopy_hook_early_receive(MigrationIncomingState *mis,
diff --git a/migration.c b/migration.c
index db860c9..63d70b6 100644
--- a/migration.c
+++ b/migration.c
@@ -99,6 +99,7 @@ MigrationIncomingState 
*migration_incoming_state_init(QEMUFile* f)
 
 void migration_incoming_state_destroy(void)
 {
+    postcopy_pmi_destroy(mis_current);
     g_free(mis_current);
     mis_current = NULL;
 }
diff --git a/postcopy-ram.c b/postcopy-ram.c
index 76f992f..8eccf26 100644
--- a/postcopy-ram.c
+++ b/postcopy-ram.c
@@ -104,7 +104,6 @@ struct PostcopyDiscardState {
 /* It's a pair of bitmaps (of the same structure as the migration bitmaps)*/
 /* holding one bit per target-page, although all operations work on host  */
 /* pages.                                                                 */
-__attribute__ (( unused )) /* Until later in patch series */
 static void postcopy_pmi_init(MigrationIncomingState *mis, size_t ram_pages)
 {
     unsigned int tpb = qemu_target_page_bits();
@@ -388,6 +387,104 @@ 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;
+
+    DPRINTF("init_area: %s: %p offset=%zx length=%zd(%zx)",
+            block_name, host_addr, offset, length, 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.
+     */
+    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 use remap_anon_pages to put
+     * a 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.
+     */
+    if (madvise(host_addr, length, MADV_NOHUGEPAGE)) {
+        perror("init_area: NOHUGEPAGE");
+        return -1;
+    }
+
+    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)
+{
+    /* Turn off userfault here as well? */
+
+    DPRINTF("cleanup_area: %s: %p offset=%zx length=%zd(%zx)",
+            block_name, host_addr, offset, length, length);
+    /*
+     * We turned off hugepage for the precopy stage with postcopy enabled
+     * we can turn it back on now.
+     */
+    if (madvise(host_addr, length, MADV_HUGEPAGE)) {
+        perror("init_area: HUGEPAGE");
+        return -1;
+    }
+
+    /*
+     * 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.
+     */
+    if (madvise(host_addr, length, MADV_NOUSERFAULT)) {
+        perror("init_area: NOUSERFAULT");
+        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)
+{
+    postcopy_pmi_init(mis, 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 */
 
@@ -404,6 +501,17 @@ void postcopy_hook_early_receive(MigrationIncomingState 
*mis,
     /* We don't support postcopy so don't care */
 }
 
+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);
+}
+
 void postcopy_pmi_destroy(MigrationIncomingState *mis)
 {
     /* Called in normal cleanup path - so it's OK */
diff --git a/savevm.c b/savevm.c
index 7f9e0b2..54bdb26 100644
--- a/savevm.c
+++ b/savevm.c
@@ -1166,6 +1166,10 @@ static int 
loadvm_postcopy_ram_handle_advise(MigrationIncomingState *mis,
         return -1;
     }
 
+    if (ram_postcopy_incoming_init(mis)) {
+        return -1;
+    }
+
     mis->postcopy_ram_state = POSTCOPY_RAM_INCOMING_ADVISE;
 
     /*
-- 
1.9.3