[Qemu-devel] [PATCH v5 26/45] Postcopy page-map-incoming (PMI) structure

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

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

The PMI holds the state of each page on the incoming side,
so that we can tell if the page is missing, already received
or there is a request outstanding for it.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 include/migration/migration.h    |  18 ++++
 include/migration/postcopy-ram.h |  12 +++
 include/qemu/typedefs.h          |   1 +
 migration/postcopy-ram.c         | 223 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 254 insertions(+)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index b44b9b2..86200b9 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -48,6 +48,23 @@ enum mig_rpcomm_cmd {
     MIG_RP_CMD_PONG,         /* Response to a PING; data (seq: be32 ) */
 };
 
+/* Postcopy page-map-incoming - data about each page on the inbound side */
+typedef enum {
+   POSTCOPY_PMI_MISSING    = 0, /* page hasn't yet been received */
+   POSTCOPY_PMI_REQUESTED  = 1, /* Kernel asked for a page, not yet got it */
+   POSTCOPY_PMI_RECEIVED   = 2, /* We've got the page */
+} PostcopyPMIState;
+
+struct PostcopyPMI {
+    QemuMutex      mutex;
+    unsigned long *state0;        /* Together with state1 form a */
+    unsigned long *state1;        /* PostcopyPMIState */
+    unsigned long  host_mask;     /* A mask with enough bits set to cover one
+                                     host page in the PMI */
+    unsigned long  host_bits;     /* The number of bits in the map representing
+                                     one host page */
+};
+
 typedef QLIST_HEAD(, LoadStateEntry) LoadStateEntry_Head;
 
 typedef enum {
@@ -69,6 +86,7 @@ struct MigrationIncomingState {
 
     QEMUFile *return_path;
     QemuMutex      rp_mutex;    /* We send replies from multiple threads */
+    PostcopyPMI    postcopy_pmi;
 };
 
 MigrationIncomingState *migration_incoming_get_current(void);
diff --git a/include/migration/postcopy-ram.h b/include/migration/postcopy-ram.h
index d81934f..e93ee8a 100644
--- a/include/migration/postcopy-ram.h
+++ b/include/migration/postcopy-ram.h
@@ -13,7 +13,19 @@
 #ifndef QEMU_POSTCOPY_RAM_H
 #define QEMU_POSTCOPY_RAM_H
 
+#include "migration/migration.h"
+
 /* Return true if the host supports everything we need to do postcopy-ram */
 bool postcopy_ram_supported_by_host(void);
 
+/*
+ * In 'advise' mode record that a page has been received.
+ */
+void postcopy_hook_early_receive(MigrationIncomingState *mis,
+                                 size_t bitmap_index);
+
+void postcopy_pmi_destroy(MigrationIncomingState *mis);
+void postcopy_pmi_discard_range(MigrationIncomingState *mis,
+                                size_t start, size_t npages);
+void postcopy_pmi_dump(MigrationIncomingState *mis);
 #endif
diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
index 611db46..924eeb6 100644
--- a/include/qemu/typedefs.h
+++ b/include/qemu/typedefs.h
@@ -61,6 +61,7 @@ typedef struct PCIExpressHost PCIExpressHost;
 typedef struct PCIHostState PCIHostState;
 typedef struct PCMCIACardState PCMCIACardState;
 typedef struct PixelFormat PixelFormat;
+typedef struct PostcopyPMI PostcopyPMI;
 typedef struct PropertyInfo PropertyInfo;
 typedef struct Property Property;
 typedef struct QEMUBH QEMUBH;
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index a0e20b2..4f29055 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -24,6 +24,7 @@
 #include "migration/migration.h"
 #include "migration/postcopy-ram.h"
 #include "sysemu/sysemu.h"
+#include "qemu/bitmap.h"
 #include "qemu/error-report.h"
 #include "trace.h"
 
@@ -49,6 +50,220 @@
 
 #if defined(__linux__) && defined(__NR_userfaultfd)
 
+/* ---------------------------------------------------------------------- */
+/* Postcopy pagemap-inbound (pmi) - data structures that record the       */
+/* state of each page used by the inbound postcopy                        */
+/* It's a pair of bitmaps (of the same structure as the migration bitmaps)*/
+/* holding one bit per target-page, although most operations work on host */
+/* pages, the exception being a hook that receives incoming pages off the */
+/* migration stream which come in a TP at a time, although the source     */
+/* _should_ guarantee it sends a sequence of TPs representing HPs during  */
+/* the postcopy phase, there is no such guarantee during precopy.  We     */
+/* could boil this down to only holding one bit per-host page, but we lose*/
+/* sanity checking that we really do get whole host-pages from the source.*/
+__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();
+    unsigned long host_bits;
+
+    qemu_mutex_init(&mis->postcopy_pmi.mutex);
+    mis->postcopy_pmi.state0 = bitmap_new(ram_pages);
+    mis->postcopy_pmi.state1 = bitmap_new(ram_pages);
+    bitmap_clear(mis->postcopy_pmi.state0, 0, ram_pages);
+    bitmap_clear(mis->postcopy_pmi.state1, 0, ram_pages);
+    /*
+     * Each bit in the map represents one 'target page' which is no bigger
+     * than a host page but can be smaller.  It's useful to have some
+     * convenience masks for later
+     */
+
+    /*
+     * The number of bits one host page takes up in the bitmap
+     * e.g. on a 64k host page, 4k Target page, host_bits=64/4=16
+     */
+    host_bits = getpagesize() / (1ul << tpb);
+    assert(is_power_of_2(host_bits));
+
+    mis->postcopy_pmi.host_bits = host_bits;
+
+    if (host_bits < BITS_PER_LONG) {
+        /* A mask starting at bit 0 containing host_bits continuous set bits */
+        mis->postcopy_pmi.host_mask =  (1ul << host_bits) - 1;
+    } else {
+        /*
+         * This is a host where the ratio between host and target pages is
+         * bigger than the size of our longs, so we can't make a mask
+         * but we are only losing sanity checking if we just check one long's
+         * worth of bits.
+         */
+        mis->postcopy_pmi.host_mask = ~0l;
+    }
+
+
+    assert((ram_pages % host_bits) == 0);
+}
+
+void postcopy_pmi_destroy(MigrationIncomingState *mis)
+{
+    g_free(mis->postcopy_pmi.state0);
+    mis->postcopy_pmi.state0 = NULL;
+    g_free(mis->postcopy_pmi.state1);
+    mis->postcopy_pmi.state1 = NULL;
+    qemu_mutex_destroy(&mis->postcopy_pmi.mutex);
+}
+
+/*
+ * Mark a set of pages in the PMI as being clear; this is used by the discard
+ * at the start of postcopy, and before the postcopy stream starts.
+ */
+void postcopy_pmi_discard_range(MigrationIncomingState *mis,
+                                size_t start, size_t npages)
+{
+    /* Clear to state 0 = missing */
+    bitmap_clear(mis->postcopy_pmi.state0, start, npages);
+    bitmap_clear(mis->postcopy_pmi.state1, start, npages);
+}
+
+/*
+ * Test a host-page worth of bits in the map starting at bitmap_index
+ * The bits should all be consistent
+ */
+static bool test_hpbits(MigrationIncomingState *mis,
+                        size_t bitmap_index, unsigned long *map)
+{
+    long masked;
+
+    assert((bitmap_index & (mis->postcopy_pmi.host_bits-1)) == 0);
+
+    masked = (map[BIT_WORD(bitmap_index)] >>
+               (bitmap_index % BITS_PER_LONG)) &
+             mis->postcopy_pmi.host_mask;
+
+    assert((masked == 0) || (masked == mis->postcopy_pmi.host_mask));
+    return !!masked;
+}
+
+/*
+ * Set host-page worth of bits in the map starting at bitmap_index
+ * to the given state
+ */
+static void set_hp(MigrationIncomingState *mis,
+                   size_t bitmap_index, PostcopyPMIState state)
+{
+    long shifted_mask = mis->postcopy_pmi.host_mask <<
+                        (bitmap_index % BITS_PER_LONG);
+
+    assert((bitmap_index & (mis->postcopy_pmi.host_bits-1)) == 0);
+
+    if (state & 1) {
+        mis->postcopy_pmi.state0[BIT_WORD(bitmap_index)] |= shifted_mask;
+    } else {
+        mis->postcopy_pmi.state0[BIT_WORD(bitmap_index)] &= ~shifted_mask;
+    }
+    if (state & 2) {
+        mis->postcopy_pmi.state1[BIT_WORD(bitmap_index)] |= shifted_mask;
+    } else {
+        mis->postcopy_pmi.state1[BIT_WORD(bitmap_index)] &= ~shifted_mask;
+    }
+}
+
+/*
+ * Retrieve the state of the given page
+ * Note: This version for use by callers already holding the lock
+ */
+static PostcopyPMIState postcopy_pmi_get_state_nolock(
+                            MigrationIncomingState *mis,
+                            size_t bitmap_index)
+{
+    bool b0, b1;
+
+    b0 = test_hpbits(mis, bitmap_index, mis->postcopy_pmi.state0);
+    b1 = test_hpbits(mis, bitmap_index, mis->postcopy_pmi.state1);
+
+    return (b0 ? 1 : 0) + (b1 ? 2 : 0);
+}
+
+/* Retrieve the state of the given page */
+__attribute__ (( unused )) /* Until later in patch series */
+static PostcopyPMIState postcopy_pmi_get_state(MigrationIncomingState *mis,
+                                               size_t bitmap_index)
+{
+    PostcopyPMIState ret;
+    qemu_mutex_lock(&mis->postcopy_pmi.mutex);
+    ret = postcopy_pmi_get_state_nolock(mis, bitmap_index);
+    qemu_mutex_unlock(&mis->postcopy_pmi.mutex);
+
+    return ret;
+}
+
+/*
+ * Set the page state to the given state if the previous state was as expected
+ * Return the actual previous state.
+ */
+__attribute__ (( unused )) /* Until later in patch series */
+static PostcopyPMIState postcopy_pmi_change_state(MigrationIncomingState *mis,
+                                           size_t bitmap_index,
+                                           PostcopyPMIState expected_state,
+                                           PostcopyPMIState new_state)
+{
+    PostcopyPMIState old_state;
+
+    qemu_mutex_lock(&mis->postcopy_pmi.mutex);
+    old_state = postcopy_pmi_get_state_nolock(mis, bitmap_index);
+
+    if (old_state == expected_state) {
+        switch (new_state) {
+        case POSTCOPY_PMI_MISSING:
+            assert(0); /* This shouldn't happen - use discard_range */
+            break;
+
+        case POSTCOPY_PMI_REQUESTED:
+            assert(old_state == POSTCOPY_PMI_MISSING);
+            /* missing -> requested */
+            set_hp(mis, bitmap_index, POSTCOPY_PMI_REQUESTED);
+            break;
+
+        case POSTCOPY_PMI_RECEIVED:
+            assert(old_state == POSTCOPY_PMI_MISSING ||
+                   old_state == POSTCOPY_PMI_REQUESTED);
+            /* -> received */
+            set_hp(mis, bitmap_index, POSTCOPY_PMI_RECEIVED);
+            break;
+        }
+    }
+
+    qemu_mutex_unlock(&mis->postcopy_pmi.mutex);
+    return old_state;
+}
+
+/*
+ * Useful when debugging postcopy, although if it failed early the
+ * received map can be quite sparse and thus big when dumped.
+ */
+void postcopy_pmi_dump(MigrationIncomingState *mis)
+{
+    fprintf(stderr, "postcopy_pmi_dump: bit 0\n");
+    ram_debug_dump_bitmap(mis->postcopy_pmi.state0, false);
+    fprintf(stderr, "postcopy_pmi_dump: bit 1\n");
+    ram_debug_dump_bitmap(mis->postcopy_pmi.state1, true);
+    fprintf(stderr, "postcopy_pmi_dump: end\n");
+}
+
+/* Called by ram_load prior to mapping the page */
+void postcopy_hook_early_receive(MigrationIncomingState *mis,
+                                 size_t bitmap_index)
+{
+    if (mis->postcopy_state == POSTCOPY_INCOMING_ADVISE) {
+        /*
+         * If we're in precopy-advise mode we need to track received pages even
+         * though we don't need to place pages atomically yet.
+         * In advise mode there's only a single thread, so don't need locks
+         */
+        set_bit(bitmap_index, mis->postcopy_pmi.state1); /* 2=received */
+    }
+}
+
 static bool ufd_version_check(int ufd)
 {
     struct uffdio_api api_struct;
@@ -71,6 +286,7 @@ static bool ufd_version_check(int ufd)
     return true;
 }
 
+
 bool postcopy_ram_supported_by_host(void)
 {
     long pagesize = getpagesize();
@@ -157,5 +373,12 @@ bool postcopy_ram_supported_by_host(void)
     return false;
 }
 
+/* Called by ram_load prior to mapping the page */
+void postcopy_hook_early_receive(MigrationIncomingState *mis,
+                                 size_t bitmap_index)
+{
+    /* We don't support postcopy so don't care */
+}
+
 #endif
 
-- 
2.1.0